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

Abstract

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 TiO2 particles and QDs with an amorphous TiO2 (am-TiO2) layer via a classical TiCl4 hydrolysis treatment plays a fundamental role to enhance the effectiveness of a recombination blocking ZnS/SiO2 barrier layer. This strategy allows construction of CdSe0.65Te0.35 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-TiO2 is superior to a crystalline TiO2 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-TiO2 layer is located at the interface between the QD sensitized photoanode and the ZnS/SiO2 barrier layer, it inhibits remarkably the charge recombination at the photoanode/electrolyte interface and prolongs the electron lifetime.