Amorphous TiO₂ Buffer Layer Boosts Efficiency of Quantum Dot Sensitized Solar Cells to over 9%

Charge recombination at an electrode/electrolyte interface is the main factor to limit the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we present a novel and facile strategy based on successive coating of a sensitized electrode with a combination of blocking layers in appropriate sequence for suppressing the charge recombination. In this scenario, modification of the exposed surface of both TiO 2 particles and QDs with an amorphous TiO 2 (am-TiO 2 ) layer via a classical TiCl 4 hydrolysis treatment plays a fundamental role to enhance the effectiveness of a recombination blocking ZnS/SiO 2 barrier layer. This strategy allows construction of CdSe 0.65 Te 0.35 QD based champion QDSCs exhibiting a new PCE record of 9.28% and a certified PCE of 9.01% under full one sun illumination. The specific nature and sequence of the layering process is critical for the gain of photovoltaic performance. Control experiments indicate that the am-TiO 2 is superior to a crystalline TiO 2 layer in serving as the passivation/buffer layer and improving the photovoltaic performance of the cells. Insight from impedance spectroscopy (IS) and open circuit voltage decay (OCVD) measurements demonstrates that when the am-TiO 2 layer is located at the interface between the QD sensitized photoanode and the ZnS/SiO 2 barrier layer, it inhibits remarkably the charge recombination at the photoanode/electrolyte interface and prolongs the electron lifetime.