Effect of Cerium Doping in the TiO₂ Photoanode on the Electron Transport of Dye-Sensitized Solar Cells

Abstract

Rare earth element cerium (Ce) with variable valence states Ce 4+ /Ce 3+ is doped in the TiO 2 photoanode for dye-sensitized solar cells (DSSCs). The anatase crystalline phase keeps unchanged, while the crystalline size decreases slightly after Ce doping. The Ce positively changes the conduction band minimum of TiO 2 due to the unoccupied Ce-4f trap states in the band gap, and the Ce 4+ is reduced to Ce 3+ when electrons are injected in the photoanode. The ceriumdoped photoanodes with special electrochemical properties severely influence the performance of DSSCs. Due to the increased electron injection, the small Ce content (0.05% and 0.1%) doped TiO 2 photoanodes improve the performance of DSSCs which is optimized to 7.65% with Ce0.1% doping (1 sun, AM1.5) compared with the one with a pure TiO 2 photoanode (7.2%). However, the Ce 4+ states effectively trap electrons in the photoanode with further increase of Ce from 0.3 to 0.9%, which is confirmed by the charge extraction method and electrochemical impedance spectroscopy (EIS); thus, it suppresses the photocurrent and the efficiency of the DSSCs but is helpful to the fill factor improvement. The trap states, mainly resting on the TiO 2 crystalline surface, are verified and effectively passivized by TiCl 4 surface treatment.

A Review on Current Status of Stability and Knowledge on Liquid Electrolyte-Based Dye-Sensitized Solar Cells

“…It also allows charge compensation mechanism to maintain a low concentration carriers [75]. We can list a series of hypervalent cations which have been successfully incorporated into the anatase crystal structure: W 6+ [76], Nb 5+ [77][78][79][80] [89]. The common observation is that hypervalent doping affects the energy of acceptor trap states.…”

Effect of growth solution concentration on the performance of gallium doped ZnO nanostructures dye sensitized solar cells (DSSCs)

“…In order to improve the performance of the DSSCs, various treatments have been carried out, such as coated layer onto active materials [12] and doping of photovoltaic materials [13][14][15][16][17][18][19][20]. The materials are doped with metallic atoms, such as indium doped ZnO [13], cerium doped TiO 2 [14], stannum doped ZnO [15], boron doped ZnO [16], alluminium doped ZnO [17].…”

“…The materials are doped with metallic atoms, such as indium doped ZnO [13], cerium doped TiO 2 [14], stannum doped ZnO [15], boron doped ZnO [16], alluminium doped ZnO [17]. Doping can also be done by non-metallic materials, such as nitrogen doped TiO 2 [18][19][20], grapheme doped TiO 2 [21] and sulfur doped TiO 2 [22].…”

“…The doping with metallic and non-metallic materials can modify physical properties, such as morphology and optical properties. The performance of DSSCs was influenced by the morphology of active materials of photoanode [13][14][15]. The band gap of active materials was lowered down, increasing the rate of free electron-hole pair and consequently improves the performance of the cells [18][19][20][21][22].…”

Application of surface chemistry at the interface of mesoporous TiO2 films for stable and high efficiency dye-sensitized solar cells.

“…162 In DSSCs, a number of studies have shown that incorporation of a rare earth dopant in the photoanode can improve the cell efficiency. 159,[163][164][165][166][167][168][169][170] The rare earth material is usually incorporated from the rare earth salt precursor into the TiO2 nanostructures during synthesis, 163,166,168,169,171 sometimes as a core/shell structure, 169 but has also been incorporated by soaking a prepared TiO2 photoanode into a rare earth salt solution followed by calcination 167 or by mixing rare earth nanoparticles with TiO2 nanoparticles followed by film preparation and calcination. 165 Upconverting, [172][173][174][175][176][177][178] 11.2% efficiency with a perovskite-based solar cell by incorporating 0.5% Yttrium into the TiO2 layer.…”