Increasing QD loading amount on photoanode and suppressing charge recombination are prerequisite for high-efficiency quantum dot-sensitized solar cells (QDSCs). Herein, a facile technique for enhancing the loading amount of QDs on photoanode and therefore improving the photovoltaic performance of the resultant cell devices is developed by pipetting metal salt aqueous solutions on TiO2 film electrode and then evaporating at elevated temperature. The effect of different metal salt solutions was investigated, and experimental results indicated that the isoelectric point (IEP) of metal ions influenced the loading amount of QDs and consequently the photovoltaic performance of the resultant cell devices. The influence of anions was also investigated, and the results indicated that anions of strong acid made no difference, while acetate anion hampered the performance of solar cells. Infrared spectroscopy confirmed the formation of oxyhydroxides, whose behavior was responsible for QD loading amount and thus solar cell performance. Suppressed charge recombination based on Mg2+ treatment under optimal conditions was confirmed by impedance spectroscopy as well as transient photovoltage decay measurement. Combined with high-QD loading amount and retarded charge recombination, the champion cell based on Mg2+ treatment exhibited an efficiency of 9.73% (Jsc = 27.28 mA/cm2, Voc = 0.609 V, FF = 0.585) under AM 1.5 G full 1 sun irradiation. The obtained efficiency was one of the best performances for liquid-junction QDSCs, which exhibited a 10% improvement over the untreated cells with the highest efficiency of 8.85%.
Keywords: charge recombination; loading amount; metal oxyhydroxide; photovoltaics; quantum dot-sensitized solar cells.