Thin Film Photoanodes

111 Mr 4.5 LtifCiJuiojlAlJiilAOji efficiencies of livMxlccnocJh.iuj( il Ci.llmii U JviJi iv rc.icjiljmv III die Win of dun liliu 

A photoanode comprised of flame oxidized carbon doped n-Ti02 films have been reported to perform water splitting with high photoconversion efficiencies [65]. While chemically modified n-Ti02 can be prepared by the controlled combustion of Ti metal in a natural gas flame the authors, in investigating this technique [66], have found reproducibility to be a challenge. Various authors [67,68,69] have discussed in considerable depth issues surrounding the stated photoconversion efficiencies of [65]. 

Cr-doped Ti02 has been widely studied for photoanode application since addition of Cr shifts the optical absorption spectrum towards the visible range, with the caveat that excess chromium doping leads to higher recombination rates. Various synthesis methods have been employed to date. For example Radecka an coworkers used r.f. sputtering to prepare up to 16 at% Cr-doped Ti02 [70]. XRD reveals that at low Cr concentration the 

120 mV less to split water as compared to that of the n-FezOs electrode [74], 

Spray pyrolysis of ethanolic solutions of Fe(acetylacetone)3 or FeCls between 370°C and 450°C onto a glass substrate are reported for the fabrication of a-Fe20s thin-film photoanodes [75]. Upon illumination by a 150 W Xe lamp samples consistently demonstrate photocurrents of 0.9 mAcm , IPCE values up to 15%, and robust mechanical stability with no signs of photocorrosion for the undoped samples. With simultaneous multiple doping of 1% A1 and 5% Ti, an IPCE of 25% can be reached at 400 nm. Zn doping is known to induce p-type character in Ee20s thin film electrodes [76]. 

---

Nanocrystalline semiconductor thin film photoanodes, commonly comprised of a three dimensional network of inter-connected nanoparticles, are an active area of photoelectrochemistiy research [78-82] demonstrating novel optical and electrical properties compared with that of a bulk, thick or thin film semiconductor [79,80]. In a thin film semiconductor electrode a space charge layer (depletion layer) forms at the semiconductor-electrolyte interface charge carrier separation occurs as a result of the internal electric... 

Morton CD, Slipper IJ, Thomas MJK, Alexander BD (2010) Synthesis and characterisation of Fe-V-O thin film photoanodes. J Photochem Photobiol A 216 209-214... 

Russak MA, Reichman J, Witzke H, Deb SK, Chen SN (1980) Thin film CdSe photoanodes for electrochemical photovoltaic ceUs. J Electrochem Soc 127 725-733... 

PEC Setup Cell Combining Polycrystalline Thin-Film Solar Cells and Photoanodes... 

PEC cell that uses polycrystalline thin-film solar cells with a photoanode. 

Jang, Y. H. Xin, X. Byun, M. Jang, Yu J. Lin, Z. Kim, D. H., An Unconventional Route to High-Efficiency Dye-Sensitized Solar Cells via Embedding Graphitic Thin Films into Ti02 Nanoparticle Photoanode. Nano Letters 2012,12 479-485. 

Chemical vapor deposition [37,38], and thermal or anodic oxidation of Ti substrates [39,40,41] have been used to prepare polycrystalline thin films of Ti02. For example, thin films of Ti02 prepared by anodic oxidation of Ti, followed by electrodeposition of In20s from 0.5 M 102(504)3 show enhanced optical absorption up to 500 nm [42] with the In203 modified electrode showing enhanced photocurrent and photovoltage partially due to the low electrical resistance (10 Q) and reduced overvoltage of the photoanode. 

The photoelectrochemical behavior of a given photoanode is dependent on its method of synthesis. Various methods, some of which we now briefly consider, such as anodic oxidation, spray pyrolysis, reactive sputtering and vapor deposition are commonly employed to make polycrystalline thin films. 

Nanocrystalline and Nanoporous Thin Film Materials as Photoanodes 219... 

---