电沉积表面修饰对染料敏化太阳电池微观性能影响机理研究

Influence of Electrodeposition Post-Treatment on Microcosmic Performances in Dye-sensitized Solar Cells

为了改善染料敏化太阳电池内电子的传输复合过程,研究者尝试不同方法制备或改性TiO2薄膜.对TiO2薄膜进行后处理,在其表面引入一层小颗粒层,是一种有效的方法并被广泛研究.通过对TiO2薄膜不同时间的电沉积表面修饰,细致研究了表面修饰后染料敏化太阳电池微观性能的变化机制.采用阳极氧化法在TiCl3水溶液中对TiO2薄膜进行电沉积后处理,将溶液pH值调至2.2,装置的反应速率由恒电位仪控制.不同沉积时间电池带边移动以及电子传输复合的动力学过程,借助强度调制光电流谱(IMPS)/强度调制光电压谱(IMVS)和电化学阻抗谱(EIS)等探测技术表征.研究表明,电沉积在TiO2薄膜表面引入了大量浅能级陷阱态,以致电势较高时电容随沉积时间延长增加明显.不同时间的电沉积表面修饰在TiO2薄膜表面形成了新的小颗粒层并改善了TiO2颗粒间接触,在改善电子注入及收集过程的同时,也有效抑制了内部电子复合.IMPS/IMVS结果表明,电沉积对动力学过程改善的效果受光强影响明显,弱光下作用更为突出.此外,电池开路电压主要受带边移动及内部复合变化影响,随沉积时间延长,表面电荷的增多使TiO2薄膜带边逐渐正移,有效改善了光电流却限制了开路电压的提升.在适合的电沉积时间下,电沉积表面修饰可以同时改善光电流和光电压.

Over the last decade, different techniques had been employed to prepare nanoporous TiO2 electrode, aiming to improve the electron transport and depress electron recombination processes in dye-sensitized solar cells （DSCs）. An effec- tive method was a post-treatment of the TiO2 films in which an extra layer of TiO2 was grown onto the TiO2 nanoparticles constituting the films. Different explanations of the working principle of this coating had been reported. In the present work, the influence of surface modification of TiO2 films on microcosmic performances of DSCs was investigated. Research was developed by the post-treatment of TiO2 films using electrodeposition method. Ti4＋ oxide films were deposited on TiO2 elec- trode by anodic oxidative hydrolysis of acidic aqueous TIC13 solutions. The pH was adjusted to 2.2 and the rate of oxidation of Ti3＋ at the anode was controlled by an almost constant anodic current using constant potential rectifier. The processes of electron recombination, transport and band edge movement were detected by intensity-modulated photocurrent spectroscopy （IMPS）/intensity-modulated photovoltage spectroscopy （IMVS） and electrochemical impedance spectroscopy （EIS）. It was found that the capacitance of TiO2 electrode evidently increased with increasing electrodeposition time at high potentials due to the risen density of shallow traps. As the formation of small particles on the surface of TiO2 films and the enhancement of particle connections, the post-treatment with different electrodeposition time improved the charge injection and transport processes and depressed the electron recombination effectively. IMPS/IMVS measurements indicated that the effects of sur- face modification almost relied on light intensities, which would perform more prominent function at low intensities. Addi- tionally, the open-circuit photovoltage （Voc） was found to be mainly effected by the conduction band edge shift and the varia- tion of charge recombination process. With increasing electrodeposition time, the conduction band was ordinally positive shift due to the increase of surface charge, which contributed an improvement of short-circuit current （Jsc） but a limitation of Voc. Overall, an optimal modification time was needed to achieve a higher Jsc and Voc.