document: the discovery of electrochemical self - assembly 
   ( esa ) of nanostructured 
   hybrid thin films of inorganic semiconductors and organic dyes has 
   opened a new synthetic route for obtaining photoanode material for 
   dye - sensitized solar cells ( dsscs ) . 
   this method bypasses the high - temperature sintering that is typically 
   needed for nanoparticulate tio2 electrodes , which prevents 
   the use of conductive plastic substrates . 
   we have previously demonstrated 
   the use of esa with the zno structures for the construction of photoanodes . 
   minor addition of water - soluble dye molecules with substituents 
   for anchoring to zno surface brought about a significant impact on 
   the crystal growth for evolution of various nanostructures and alteration 
   of the crystallographic orientation of the film . 
   importantly , the 
   coprecipitation of dye molecules does not necessarily deteriorate 
   the crystallinity of zno . in the case of zno / eosin 
   y ( ey ) hybrid thin 
   films , vertically aligned interconnected and crystalline nanowires 
   of zno are formed . the space between the zno nanowire 
   is filled with aggregates of ey . 
   the solid ey can be completely removed 
   by soaking the hybrid film in a mild alkaline such as dilute koh aq . 
   thus , prepared zno thin films , 
   consisting of large single - crystalline grains with internal porous 
   structure , to be called  porous crystal zno  , have large 
   surface area for adsorption of photosensitizer dye in a large amount 
   and high crystallinity for efficient transport of electrons ; therefore , 
   it can achieve high incident photon to current conversion efficiency 
   ( ipce ) of around 90% . with the dssc application 
   in mind , it would be highly interesting 
   to find a compatible system for fabricating sensitized photocathodes . 
   recently , powar et al . 
   have succeeded in achieving 1.3% conversion 
   efficiency for a dssc in an inverted structure employing a porous 
   p - nio electrode sensitized with a specially designed dye to achieve 
   a high rectification with kinetically reversible co(ii / iii ) ethylene 
   diamine complex electrolyte . 
   we have been 
   seeking to perform cathodic electrodeposition of cuscn , a p - type , 
   wide - bandgap semiconductor , into highly crystallized thin films at 
   low temperature . 
   cuscn has been frequently used as a hole conductor in nanostructured 
   solar cells and also as a sensitized photocathode in combination with hole - injecting 
   dyes . 
   therefore , esa of cuscn - based hybrid thin films could 
   serve nicely as a counterpart to the well - established zno - based hybrid 
   systems . 
   our first attempt for esa of cuscn hybrid system was 
   to employ 
   dye molecules having soft lewis basic ncs groups . on the basis of the hard and soft , acid and base 
   ( hsab ) principle , choice of dyes equipped with hard lewis basic carboxylate 
   is suited for binding to hard lewis acidic ti(iv ) sites of tio2 or zn(ii ) sites of zno . because cu(i ) of cuscn is a typical 
   soft lewis acid , the soft sulfur atom of the ncs should be 
   a good match . as such 
   , dyes having ncs groups , the popular 
   n3 dye ( ru(dcbpy)2(ncs)2 , dcbpy = 2,2-bipyridine-4,4-dicarboxylic 
   acid ) and fltc ( fluorescein isothiocyanate ) were added to the bath 
   for electrodeposition of cuscn . 
   as expected , colored cuscn thin films 
   incorporating n3 and fltc were obtained , while ey added for comparison 
   did not cause any change for the formation of cuscn , which is of course 
   normally colorless . 
   the addition of n3 and fltc also brought about 
   the evolution of characteristic nanostructure of cuscn , clearly indicating 
   their action as structure directing agents ( sdas ) . 
   the electrodeposited 
   cuscn / dye hybrid thin films exhibited dye - sensitized photocathodic 
   properties , evincing the intimate chemistry between cuscn and dyes 
   having soft basic anchors , which appear to be the key for hole injection 
   from the dye excited state . following the success with the above - mentioned 
   strategy , the idea 
   further developed to try substituting cu(i ) of cuscn with cationic 
   dyes instead of substituting ncs with dyes having 
   ncs group . among commercially readily available dyes , we have 
   employed rhodamine b ( rb ) , which is cationic because of the presence 
   of an ammonium group . 
   this strategy indeed showed positive results 
   as we have seen a clear effect of rb as an sda for formation of nanostructure 
   and as a cause of changes in crystallographic orientation of cuscn . 
   however , it was not possible to extract the loaded 
   rb molecules by any kind of post treatment to obtain highly porous 
   structure as in the case of the zno / ey hybrid system . because the 
   mechanism of cuscn electrodeposition was poorly understood at the 
   time of the previous work , the conditions were not properly chosen 
   to achieve hybrid thin films with composition similar to that of zno / ey , 
   for which ey could occupy close to half of the volume of the precipitated 
   solid . in this work , 
   we present a method for esa of hybrid cuscn / rb 
   nanoporous 
   films in which the rb sda may be nearly completely removed . by varying 
   the relative concentration of cu and scn 
   , we can change the crystal orientation of the resulting nanostructure 
   with respect to the substrate . 
   we explore several preliminary dyes 
   and show photoinduced hole transfer to the cuscn ; in addition , we 
   tested the best systems in photoelectrochemical studies to check the 
   dye - sensitized photocathodic properties . at this stage , 
   we still do 
   not have a good combination of dye and electrolyte for cuscn . 
   however , 
   the recent progress with the photocathodic dssc presents a new opportunity 
   to improve the efficiency of dye - sensitized cathode systems that can 
   eventually be combined with existing sensitized anodes for realization 
   of a tandem solar cell to achieve high efficiencies in very simple 
   structures . 
   inorganic chemicals such as lithium thiocyanate dihydrate ( liscn2h2o , kishida ) , copper(ii ) perchlorate hexahydrate ( cu(clo4)26h2o , sigma - aldrich ) , and lithium 
   perchlorate ( liclo4 , sigma - aldrich ) and organic solvents 
   such as n , n - dimethylacetamide ( dma , wako ) and ethanol 
   ( wako ) were of special grade and used as purchased . 
   fluorine - doped tin oxide ( fto ) coated 
   transparent conductive glass ( sheet resistance , 78 /sq , 
   1.1 mm thick soda lime glass , asahi - du , asahi glass ) was used as the 
   substrate to electrodeposit the cuscn thin films . 
   milli - q ultrapure 
   water ( > 18 m ) was used throughout the experiments . 
   the fto glass was cut into 25  25 mm , degreased 
   by ultrasonically cleaning in detergent and acetone , and finally rinsed 
   with water . 
   it was mounted into a specially designed electrode holder 
   for a homemade rotating disc electrode ( rde ) system . 
   the active area of the fto glass electrode was regulated 
   to a 22 mm diameter circle concentric to the rotating electrode holder 
   by applying a masking tape ( nitto denko n-300 ) . 
   the use of a rde system 
   to introduce laminar flow is essential for obtaining cuscn thin films 
   with perfect homogeneity and with a high reproducibility because the 
   reaction occurs under the mass transport limited regime . 
   the fto glass rde that serves as a working electrode is placed with 
   the active surface down and in the center of the electrochemical cell 
   of a cylindrical shape , equipped with a water - jacket for temperature 
   control ( 25 c ) , together with auxiliary electrodes , a pt wire 
   counter and a ag / agcl reference . 
   a mixture of water and ethanol ( 1:3 
   in volume ratio ) was used for preparation of the deposition bath . 
   cu(clo4)2 and liscn were dissolved at 9 and 
   3 or 3 and 9 mm for cu rich or scn rich bath , respectively , while 0.1 m liclo4 was also 
   added as the supporting electrolyte . 
   a small amount of rb up to 1.0 
   mm was added to obtain cuscn / rb hybrid thin films . 
   a hokuto - denko 
   hsv-100 electrochemical system was used for potential control and 
   current monitoring . 
   cathodic electrolysis at + 0.2 v ( vs ag / agcl ) for 
   5 min and with a rotation speed of 500 rpm resulted in cuscn thin 
   films which were washed with water , dried under air at room temperature , 
   and subjected to characterization . 
   vis absorption 
   spectra of the films were measured in 
   transmission on a hitachi u-4000 or a perkinelmer lambda 1050 spectrophotometer . 
   fluorescence spectra of the film samples were measured on a photon 
   technology international quantamaster40 equipped with two double - monochromators 
   and a cooled pmt detector . aside from the cuscn / rb hybrid thin film , 
   cuscn hybrid with fluorescein isothiocyanate ( fltc ) , nile blue ( nb ) 
   , 
   cresyl violet ( cv ) , 3,4,9,10-perylenetetracarboxylic acid 
   diimide ( ptcdi ) , and quinacridone ( qd ) , as well as thin solid films 
   of only these chromophores , were prepared for comparison in the fluorescence 
   study . 
   those of rb , fltc , nb , and cv were prepared by hybrid electrodeposition 
   and spin coating their 1 mm solutions in ethanol on a slide glass , 
   while those of ptcdi and qd were prepared by vacuum evaporation either 
   onto an electrodeposited porous cuscn or on a slide glass . 
   surface 
   morphology of the films was observed by field emission scanning electron 
   microscopy ( fe - sem , hitachi s-4800 or jeol jsm-6700f ) . 
   crystallographic 
   characterization of the film was conducted by measuring x - ray diffraction 
   ( xrd ) patterns on a rigaku rint ultima iii instrument . 
   the amount 
   of rb loaded into the film was determined by dissolving 
   a known area of the film into a known volume of ammonia solution and 
   measuring its absorption spectrum . 
   the amount of electrodeposited 
   cuscn was determined by measuring the amount of cu in 
   the ammonia solution dissolving the film according to the classical 
   colorimetric analysis method , employing 
   sodium n , n - diethyldithiocarbamate 
   trihydrate ( ddtc , wako ) to chelate copper ion for extraction with 
   ethyl acetate which exhibits a strong absorption at 436 nm (  
   = 1.3  10 m  cm ) . 
   comparison with the amount of consumed charge yields faradaic 
   efficiency for the electrodeposition of cuscn . 
   a part of the loaded 
   rb molecules could also be extracted by soaking the film in dma . from 
   comparison of the absorption spectra before and after the dma treatment , 
   the fraction of the extractable rb could be determined . 
   several thin - film 
   samples after the dma treatment were scratched off the substrate . 
   the surface area of powder samples prepared in this manner was determined 
   by brunauer 
   teller ( bet ) analysis of the kr gas 
   sorption measurement conducted on a micromeritics tristar ii 3020 
   system . 
   photoelectrochemical measurements on cuscn thin film 
   electrodes 
   have been performed in a three - electrode setup with a pt wire counter 
   and a saturated calomel reference electrode ( sce ) . 
   porous cuscn thin 
   films were sensitized by soaking them in a 1.0 mm rb aqueous solution 
   for 1 h. a 0.1 m aqueous solution of methylviologen dichloride ( mv , sigma - aldrich ) was used as the electrolyte . 
   the electrode 
   was illuminated from its front side with a visible light generated 
   by a 500 w xe lamp ( ushio ) filtered by uv ( < 420 nm ) and ir ( > 800 
   nm ) cutoff filters ( intensity , 100 mw  cm ) . 
   direct crystallization of -cuscn 
   occurs as a consequence 
   of cathodic reduction of cu in the presence of scn both from aqueous and ethanolic solutions . 
   rhodamine b is commercially provided as chloride 
   and is well - soluble both to water and ethanol . 
   30 m when 0.1 m liclo4 was 
   added to water as a supporting electrolyte because of the salting - out 
   effect , making it difficult to achieve a high loading of rb to cuscn . 
   on the other hand , ethanol dissolved rb too well to hinder its loading 
   to cuscn . 
   therefore , a mixture of water and ethanol ( 25:75 volume 
   ratio ) was chosen as the solvent that provided good solubility of 
   all chemicals and achieved an efficient loading of rb molecules during 
   electrochemical growth of cuscn . 
   our previous studies on electrodeposition 
   of cuscn employing a 
   rotating disk electrode revealed that the growth of cuscn is typically 
   limited by transport of complexes of cu and scn that form in solution , achieving practically 100% faradaic efficiency 
   for the formation of cuscn . in aqueous 
   solutions , only a 1-to-1 complex 
   is formed , while a neutral 1-to-2 complex is also formed and participates in 
   the electrochemical reaction in ethanolic solutions containing excess 
   of scn . 
   thus , the 
   overall reaction is expressed by eq 1 for the 
   aqueous solution and both eqs 1 and 2 operate in the ethanolic solution.12the chronoamperograms measured 
   during the 
   electrodeposition can be seen in figure 1 . 
   following the initial rise of the current , 
   diffusion - limited steady - state 
   current is reached both for the cu rich and scn rich solutions . however , 
   this should reflect the formation 
   of a bis - coordinated cu(ii ) thiocyanato complex which has a diffusion 
   coefficient that is somewhat higher than that of the monocoordinated 
   complex in ethanol as revealed in our electrochemical analysis . 
   the addition of rb to the bath causes a slight 
   decrease of the steady - state current in the scn rich bath , whereas a slight increase of the current was observed 
   in the cu rich bath , which could be caused by the chemical 
   interaction of the complexes with rb molecules . 
   even though the addition 
   of rb caused a slight decrease of faradaic efficiency for the precipitation 
   of cuscn ( vide infra ) , the film thickness increased linearly with 
   the consumed charge ( see figure 1s of supporting 
   information ) . 
   as the current is almost constant , the film thickness 
   can simply be controlled by the time of the electrolysis . 
   however , 
   it should be mentioned that the high addition of rb at 1.0 mm brings 
   about a characteristic change in the initial profile of the current . 
   in such baths , 
   the current stays small in the beginning of the electrolysis 
   then abruptly increases to achieve the steady - state current . 
   the surface 
   of the fto glass substrates was observed by sem before and after the 
   jump of the current ( figure 2 ) . 
   there is apparently 
   no change before the jump as the bare surface of the fto layer is 
   seen . 
   after the jump , tiny cuscn particles are deposited , especially 
   at the bottom of the valleys and along the ridges of the pyramidal 
   fto grains . although the reason for the incubation time is unclear , 
   it is probable that rb molecules are adsorbed on the fto surface , 
   hindering the nucleation of cuscn . 
   chronoamperograms measured during electrodeposition 
   of cuscn and 
   cuscn / rb hybrid thin films onto an fto coated glass rde (  = 
   500 rpm ) at + 0.2 v ( vs ag / agcl ) in ethanol / water ( 75/25 , v / v ) mixed 
   solutions containing cu(clo4)2 and liscn in 
   cu rich ( 9 and 3 mm , respectively ) and scn rich ( 3 and 9 mm , respectively ) compositions ; 0.1 m liclo4 as a supporting electrolyte ; and 0 , 0.1 , or 1.0 mm rb . 
   sem pictures of the surface of the fto glass substrates 
   after electrolysis 
   for 20 s ( a ) and 30 s ( b ) in an ethanol / water ( 75/25 , v / v ) mixed solution 
   containing 3 mm cu(clo4)2 , 9 mm liscn , 0.1 m 
   liclo4 , and 1.0 mm rb . 
   cuscn / rb hybrid thin films were electrodeposited for 5 min 
   both 
   from scn rich and cu rich baths while 
   changing the concentration of rb . 
   the morphology of the pure cuscn 
   film looks totally different for those deposited from scn rich and cu rich baths ( panels a1 and b1 of figure 3 , respectively ) . 
   the former consists of large rounded 
   hexagonal columnar particles , whereas the latter shows assemblies 
   of spiky particles . 
   rhombohedral -cuscn has an elongated hexagonal 
   unit cell with lattice constants of a = b = 3.857  and c = 16.449  . as discussed below , the xrd patterns of the 
   films indicate that films of a1 and b1 are oriented for the c - axis perpendicular with the substrate . 
   the hexagonal faces 
   of the deposits in a1 should thus correspond to the ( 003 ) planes of 
   cuscn , while those faces creating the spikes should probably be of 
   the ( 101 ) planes . 
   such differences can be caused by the change of 
   the stability of the crystal faces by the change of the chemical composition 
   of the bath influencing the dissolution and recrystallization of cuscn 
   during the electrodeposition ( eq 3).3when rb is added to the bath , purple - colored 
   cuscn / rb hybrid thin films were obtained . as the concentration of 
   rb increased , the color of the film got deeper , indicating the increased 
   loading of rb into the film . at the same time , the morphology of the 
   film drastically changed ( panels a2 , a3 , b2 , and b3 of figure 3 ) . 
   as discussed later , the loaded rb 
   molecules can almost completely be extracted by dipping the film shown 
   in a3 in dimethylacetamine ( dma ) , making it highly porous . 
   the shape 
   of the particles differs from sample to sample , especially as recognized 
   from the cross sections , indicating anisotropic crystal growth promoted 
   by rb addition . 
   sem photographs of cuscn and cuscn / rb hybrid thin films 
   electrodeposited 
   from scn rich ( a ) and cu rich ( b ) 
   baths containing 0 ( a1 and b1 ) , 0.3 ( a2 and b2 ) and 1.0 mm ( a3 and 
   b3 ) rb . a1a3 and 
   b1b3 
   correspond to the cross section of a1a3 and b1 b3 , 
   respectively . 
   changes of xrd patterns 
   on rb addition are shown in figure 4 for scn rich and cu rich baths . 
   all these patterns 
   indicate diffraction peaks assigned 
   to -cuscn aside from those originating from sno2 of the fto substrate . the relative intensity of the diffraction 
   peaks of the film samples , however , are different from those of the 
   powder diffraction standard . 
   it is also changes for different rb concentrations 
   and for scn rich ( a ) and cu rich ( b ) 
   baths , indicating changes of their crystallographic orientation . 
   two 
   representative diffraction peaks arising from the ( 003 ) and the ( 101 ) 
   planes are taken to evaluate the orientation change . 
   while the ( 003 ) 
   planes are perpendicular to the c - axis , the ( 101 ) 
   planes are nearly parallel to the c - axis , crossing 
   with the ( 003 ) planes at 78.5 angle because of the elongated 
   unit cell structure . 
   therefore , the relative change of the ( 003 ) and 
   ( 101 ) peak intensities is a good measure for examining how the c - axis of cuscn is oriented with respect to the substrate 
   plane . according to the method described in the literature , 
   the orientation indices ( oi ) are calculated 
   as follows . the intensity factor ( if ) of the standard powder sample 
   is calculated for the respective crystal planes as45taking the intensities indicated in ref ( 23 ) . 
   the if of the film samples are calculated from the ( 003 ) and ( 101 ) peak 
   counts of each measured xrd pattern.67the ratio of the if of the film with respect 
   to that of the powder standard is defined as the oi.89when oi(hkl ) is 
   larger than 1 , the film has a tendency to orient ( hkl ) planes in parallel with the substrate ; when smaller than 1 , just 
   the opposite . 
   pure cuscn thin films electrodeposited without rb show high 
   oi(003 ) , indicating their preferential orientation of the c - axis perpendicular with the substrate , irrespective of 
   the scn rich and cu rich bath compositions . 
   such preferential orientation nicely matches with the arguments for 
   their morphological features described above , namely , the hexagonal 
   facet of the columnar grain in figure 3a1 and 
   the bevels of the spiky grains in figure 3b1 
   corresponding to the ( 003 ) and ( 101 ) planes , respectively . 
   minor addition 
   of rb to the bath then drastically increases the oi(101 ) upon decrease of oi(003 ) , indicating the change of the 
   crystallographic orientation to lay down the c - axis 
   in parallel with the substrate . 
   such preference is most prominent 
   when [ rb ] = 0.3 mm , for both the scn rich and cu rich baths . 
   however , the higher addition of rb abruptly 
   changes the orientation back to the one in which the c - axis is perpendicular with the substrate in the case of the scn rich bath , whereas the oi(101 ) value only 
   moderately decreases for the cu rich bath . 
   consequently , 
   highly porous cuscn thin films with totally different crystallographic 
   orientations , namely , the c - axis perpendicular and 
   parallel with the substrate are obtained for the highest end of the 
   rb addition to the scn rich and cu rich baths , respectively . 
   however , it is obvious that 
   such changes are caused by the difference of the chemical stability 
   of the facets of cuscn crystals in different environments , not only 
   by the scn / cu balance but also by 
   the added rb molecules . 
   xrd patterns of cuscn and cuscn / rb hybrid thin 
   films electrodeposited 
   from scn rich ( a ) and cu rich ( b ) 
   baths containing 0 ( a ) , 0.1 ( b ) , 0.2 ( c ) , 0.3 ( d ) , 0.4 ( e ) , 0.5 ( f ) , 
   0.7 ( g ) , and 1.0 mm ( h ) rb . change of crystallographic orientation of cuscn and cuscn / rb hybrid 
   thin films by changing concentration of rb added to the scn rich and cu rich baths . 
   the amount of rb loaded into cuscn during electrodeposition 
   for 
   300 s from the scn rich and cu rich 
   baths is plotted as a function of rb concentration ( figure 6 ) . 
   the amount of rb precipitated together with cuscn 
   increases as its concentration in the bath increases , although not 
   proportionally but showing a leveling off trend . the loading efficiency 
   in the scn rich bath is clearly higher than that 
   in the cu rich , especially for the low rb concentration 
   range . 
   some properties of the cuscn / rb hybrid thin films electrodeposited 
   from the scn rich bath are summarized in table 1 . 
   change of the amount of rb loaded into cuscn as a function 
   of rb 
   concentration added to the scn rich and cu rich baths . calculated for  = 500 rpm 
   from levich equation by employing the bulk concentration of rb and 
   its diffusion coefficient in water at 25 c ( 3.2  10 cm  s ) . 
   calculated by dividing the amount 
   of rb loaded into the film by the amount of rb transported to the 
   electrode surface in 300 s. calculated by using the formulas 
   weight of cuscn ( 121.6 g  mol ) , the density 
   of cuscn ( 2.84 g  cm ) , the molar weight 
   of rb ( 479.02 g  mol ) and the density of 
   rb solid ( 0.79 g  cm at 20 c ) . 
   the volume of the void was calculated 
   by subtracting the volumes of cuscn and rb from the total volume of 
   the film determined from the film thickness . 
   increase of the concentration of rb in the bath led 
   to a slight 
   decrease of the consumed charge because of the decrease of the steady - state 
   current and the presence of the incubation time for [ rb ] = 1.0 mm . 
   at the same time , faradaic efficiency for the precipitation of cuscn 
   gradually decreased . 
   the film thickness significantly decreased , as 
   seen in the crosssectional sem pictures in figure 3 . while the amount of electrodeposited cuscn decreased , the 
   amount of precipitated rb increased . 
   the change of the film thickness , 
   however , is mostly caused by the change of the porosity as seen in 
   the volume ratio for cuscn , rb , and void for the hybrid film . as the 
   diffusion coefficient of the rb molecule could be found only as measured 
   in water solution , we took this value to calculate the flux of rb 
   for its given concentration under the rotating condition employed 
   in this study . 
   the sticking efficiency of rb was then estimated by 
   calculating the fraction of rb loaded into the film as compared to 
   its maximum amount transported toward the electrode surface during 
   the electrolysis . 
   the highest efficiency of 17.5% was achieved for 
   [ rb ] = 0.1 mm , and that value decreased as the bulk concentration 
   got higher . 
   it is obvious that the precipitation of rb is not under 
   the control of its transport but rather its stability or rate of attaching 
   to cuscn . 
   when the molar amounts of precipitated cuscn and rb are 
   determined , the fraction of the volume occupied by these components 
   in the hybrid film can be calculated by taking their molar weight 
   and density , either taking into account or not taking into account 
   the total volume of the film . 
   the cuscn : rb ratio gives a rough idea 
   up to how much volume of the precipitated solid can be occupied by 
   rb . 
   an approximately 2:1 ratio seems to be reachable for this system , 
   which is equivalent to that for the zno / eosin y hybrid system reported 
   elsewhere . 
   the cuscn : rb : void ratio correlates 
   to the porosity of the film . as shown in the following section , the 
   loaded rb molecules can be removed from the hybrid films with high 
   rb loading , leaving some empty space within the cuscn grains . the 
   voids in the as - deposited films occur from spaces between the cuscn / rb 
   hybrid grains , while that occupied by rb is converted to the tiny 
   pores formed inside cuscn grains after extraction of rb . 
   when the hybrid films are soaked in dimethylacetamide ( dma ) , the 
   films were bleached as the rb molecules were extracted , as seen from 
   the change of the absorption spectra before and after the treatment 
   ( figure 7 ) . 
   for the films with small rb loading , 
   rb molecules could be only partly removed , whereas those with high 
   rb loading allowed almost complete desorption of rb . the film with 
   the highest rb loading , namely , that deposited from the scn rich bath containing 1.0 mm rb , became nearly colorless because 
   97% of the loaded dye was removed as estimated from the absorbance 
   change at the maximum of rb absorption . 
   as discussed above , the extraction 
   of rb should result in tiny nanopores enlarging the surface area of 
   the cuscn films . 
   teller 
   analysis of kr sorption measurements ( figure 8) . the surface area of about 6 m  g is already reached for the film deposited from the cu rich bath without rb . 
   it only moderately increases by hybridization 
   with rb and its extraction for the cu rich baths . on 
   the other hand , that of the film deposited from the scn rich bath results in only about 4 m  g without rb , and it greatly increases up to 12.6 m  g when [ rb ] = 1.0 mm . the roughness factor ( rf ) , defined 
   as the ratio of the actual surface area per projected film area , of 
   about 17 
   is reached as calculated from the amount of electrodeposited 
   cuscn shown in table 1 . 
   considering the small 
   film thickness of 0.8 m , this roughness factor is reasonably 
   high because rf of several hundred can be reached when the thickness 
   is increased to a few tens of micrometers . 
   these thicknesses and rf 
   values are comparable to those of materials typically used for dye - sensitized 
   solar cells . using the reported growth conditions 
   , we were able to 
   extend the growth time and film thickness by roughly a factor of 5 
   before inducing any cracking in the film . 
   transmission absorption 
   spectra of as - electrodeposited cuscn / rb 
   hybrid thin films ( solid lines ) and those after soaking the films 
   for 1 h in dimethylacetamide ( dma ) ( dashed lines ) . 
   the cuscn / rb thin 
   films were electrodeposited from scn rich ( black 
   lines ) and cu rich ( gray lines ) baths containing 0.1 
   ( thin lines ) or 1.0 mm ( thick lines ) of rb . 
   change of specific surface area of cuscn / rb hybrid thin films after 
   extraction of rb by dma treatment as determined by kr sorption measurements . as we have succeeded in obtaining 
   highly porous crystalline cuscn 
   thin films , 
   it is of significant interest to check its usefulness 
   as a dye - sensitized photocathode . 
   however , no stably adsorbed sensitizer 
   dye for efficient hole injection to cuscn has been previously discovered . 
   we first checked fluorescence quenching for several fluorescent dye 
   molecules attached to cuscn , such as fluorescein isothiocyanate ( fltc ) , 
   cresyl violet ( cv ) , nile blue ( nb ) , 3,4,9,10-perylene tetracarboxylic 
   acid diimine ( ptcdi ) , quinacridone ( qc ) , and rb . 
   fltc can be coelectrodeposited 
   with cuscn because of the presence of a soft basic thiocyanate moiety 
   that is expected to act as an anchor to the soft acidic cu(i ) sites 
   of cuscn . 
   the electrodeposited cuscn / fltc 
   hybrid thin film in fact exhibited dye - sensitized photocathodic behavior 
   upon visible light illumination . 
   addition 
   of nb and cv to the deposition bath for cuscn also resulted in formation 
   of hybrid thin films because of their cationic character by the presence 
   of ammonium group , the same as that of rb . 
   ptcdi and qc lack such 
   chemical affinity to cuscn , so they were simply vacuum evaporated 
   on top of the porous cuscn . 
   all of these molecules exhibit fluorescence 
   in solution , but nb and cv actually did not show measurable fluorescence 
   in solid state . whereas no quenching was observed for ptcdi and qc , 
   fluorescence of fltc and rb was strongly quenched for their electrodeposited 
   hybrid thin films . 
   in particular , that of rb was almost totally quenched 
   as shown in figure 9 , while imperfect quenching 
   was observed in the case of the cuscn / fltc hybrid ( see figure 2s of supporting information for the spectra ) . because 
   the valence band edge of cuscn is expected to lie around 5.3 
   ev ( vs vac ) , the highest occupied molecular orbital level of all these 
   dye molecules is deep enough to transfer holes to cuscn from a thermodynamic 
   point of view . 
   it is supposed that the strong chemical affinity of 
   fltc and rb to cuscn is crucial for hole injection to take place actually , 
   unlike ptcdi and qc which are only in physical contact with the surface 
   of cuscn . 
   absorption and fluorescence spectra of electrodeposited cuscn / rb 
   hybrid thin film ( solid lines ) , solid rb thin film prepared by spin 
   coating ( dashed lines ) , and 20 m rb solution in ethanol ( dotted 
   lines ) . 
   the excitation wavelength for the film samples and the solution 
   were 535 and 530 nm , respectively . 
   the fluorescence spectrum of the 
   rb solution is attenuated for better comparison with other spectra 
   because it is far stronger than the other samples . 
   monomeric rb molecules in solution exhibit a sharp 
   absorption 
   peak at 545 nm and a weak shoulder around 505 nm . 
   a strong and sharp 
   fluorescence spectrum occurs like a mirror image of the absorption 
   spectrum , exhibiting a peak at 574 nm and a weak shoulder around 620 
   nm . 
   the solid thin film of rb aggregate shows a characteristic change 
   of the absorption spectrum with a maximum at 579 nm and another distinctive 
   peak at 541 nm . 
   it has been shown that dimerization of rb molecules 
   in solution leads to an increase of the abosorbance of the short side 
   shoulder because of enhanced intermolecular interaction in parallel 
   arrangement of the chromophore , namely , in h - aggregate form . 
   the great enhancement of the blue - side shoulder band to become a 
   clearly distinguished satellite peak for the solid rb film is obviously 
   caused by the strong electronic interaction in the molecular solid 
   in h - aggregate form . 
   the sharp peak at 613 nm should reflect a monomolecularly 
   confined fluorescence band , which is also red - shifted compared to 
   that of the rb monomer solution . on the other hand , 
   the broad character 
   centered at 687 nm should be related to the transition involving the 
   intermolecular band , which exists only in the aggregates . 
   the absorption 
   spectrum of the electrodeposited cuscn / rb hybrid thin film closely 
   resembles that of the solid rb thin film , exhibiting a character for 
   the h - aggregate . 
   however , both peaks are blue - shifted to 536 and 570 
   nm for aggregate and monomer bands , respectively , indicating different 
   environments of the rb molecules which are subjected to chemical interaction 
   with cuscn . 
   because characteristic fluorescence was clearly monitored 
   for rb in the solid state , the total quenching of the fluorescence 
   in the hybrid film should be caused by hole transfer from the exited 
   state of rb to the valence band of cuscn . 
   the electrodes were the pure cuscn with a 
   relatively high surface area , that electrodeposited from cu rich bath without rb , and a highly porous cuscn made by electrodeposition 
   from a scn rich bath containing 1.0 mm rb which 
   then was removed by the dma treatment . 
   thus , we prepared 
   a dye - sensitized photocathode with the rb dye shown to undergo photoinduced 
   hole transfer . 
   however , the lack of a suitable redox electrolyte is 
   a significant problem for studying photocathodic sensitization of 
   cuscn . 
   iodide / triiodide redox electrolyte typically 
   used in dsscs reacts with cuscn to convert it to cui that dissolves 
   rather well in many polar organic solvents . 
   adsorption of rb molecules 
   to cuscn was unfortunately not so stable , as recognized by the fact 
   that the electrolyte solution was clearly colored by desorbed rb both 
   for organic and aqueous solutions . 
   for this reason , it was not useful 
   to use co complex redox systems , which are kinetically highly reversible , 
   because fast recombination from the uncovered surface of cuscn or 
   exposed fto actually killed the voltage under illumination . stably 
   adsorbed highly rectifying dyes are needed for effective use of co 
   redox , which are missing at this stage . 
   thus , we have employed an aqueous solution of methylviologen chloride 
   as the electron acceptor . 
   the electrode was reasonably stable in this 
   electrolyte and exhibited a clear photocathodic action under visible 
   light illumination as shown in figure 10 . 
   pure 
   cuscn film sensitized with rb exhibits about 0.2 v photocurrent onset 
   voltage and 22 a cm photocathodic current ; 
   these values increased to ca . 
   0.3 v and 32 a cm for the porous cuscn electrode prepared by hybrid electrodeposition 
   with rb , extraction of rb , and readsorption of rb . 
   clearly , enlarged 
   surface area made the color of the film more intense than that of 
   the pure cuscn , obviously contributing to the increased current . 
   poorly 
   rectified dark current for pure cuscn ( figure 10a ) can be associated with the the bare fto surface being in contact 
   with the electrolyte , allowing direct charge transfer to methylviologen . because the 
   porous crystalline cuscn ( figure 10b ) covers 
   the fto better than pure cuscn , the dark current is well - rectified 
   and higher voltage is achieved . despite efforts to find a stable dye 
   electrolyte 
   solution combination , the rb dye still desorbs from the surface during 
   measurement , likely contributing to the unusually low photocurrent 
   . i  v curves measured at 
   bulk cuscn ( a ) electrodeposited without rb and porous crystalline 
   cuscn ( b ) electrodeposited with 1.0 mm rb and rb subsequently removed 
   by dma treatment , measured in the dark ( hashed lines ) and under illumination 
   ( solid lines ) with visible light ( 100 mw  cm ) generated by a 500 w xe lamp equipped with uv and ir cutoff filters . 
   the cuscn films were sensitized by readsorbing rb by soaking in a 
   0.5 mm rb aqueous solution for 1 h. the electrolyte was a deaerated 
   aqueous solution of 0.1 m methylviologen chloride . 
   we have developed a method for obtaining a highly 
   porous and nicely 
   crystallized p - cuscn thin film by electrodeposition . by selection 
   of the bath composition , 
   it has become possible to load rb molecules 
   in an amount to occupy as much as 30% of the total volume of precipitated 
   solid , from which the loaded rb could be removed by soaking the film 
   in dma . 
   such a process can now be regarded as a counterpart of the 
   entire technology developed for zno / eosin y hybrid electrodeposition 
   for processinghigh - performance 
   porous crystalline zno - based dye - sensitized photoanodes . 
   porous structures are created by the rb molecules 
   within highly crystallized cuscn . not only the porous nanostructure 
   but also the crystallographic orientation of cuscn could be controlled 
   by the choice of the bath composition . 
   the resulting porous crystalline 
   cuscn thin film has been utilized as dye - sensitized photocathode to 
   prove its usefulness as a counterpart of dye - sensitized zno photoanodes . 
   however , limited surface area as well as the lack of good hole - injecting 
   dye stable on the cuscn surface and suitable redox electrolyte remain 
   as challenges for efficiency improvement of the photocathode . because 
   recent studies have discovered a good sensitizer for p - nio in combination 
   with co complex redox systems , there is 
   a good hope of finding one for p - cuscn . 
   the successfully constructed 
   efficient dye - sensitized cuscn photocathode can be combined with existing 
   dye - sensitized photoanodes to achieve high - efficiency tandem dsscs 
   in a very simple structure sandwiching a common redox electrolyte 
   solution by two photoelectrodes .
summary: nanostructured 
   hybrid thin films of cuscn and rhodamine b ( rb ) 
   are electrochemically self - assembled ( esa ) by cathodic electrolysis 
   in an ethanol / water mixture containing cu2 + , scn , and rb . by selecting the solvent , cu2+/scn ratio , and the concentration of rb , we demonstrate several control 
   parameters in the film formation . 
   high loading of rb into the film 
   has been achieved to reach a cuscn : rb volume ratio of approximately 
   2:1 . 
   the rb solid could almost completely be extracted from the hybrid 
   film by soaking the film in dimethylacetamide ( dma ) , leading to a 
   large increase of the surface area . 
   the crystallographic orientation 
   of the nanostructure with respect to the substrate can be controlled . 
   efficient quenching of fluorescence of rb has been observed for the 
   cuscn / rb hybrid film , implying hole injection from rb excited state 
   to cuscn . 
   photoelectrochemical study on the porous crystalline cuscn 
   obtained after the dma treatment and sensitized with rb revealed sensitized 
   photocathodic action under visible light illumination , indicating 
   the potential usefulness of the porous cuscn electrodes for construction 
   of tandem dye - sensitized solar cells .