Polyoxometalate doped tin oxide as electron transport layer for low cost, hole-transport-material-free perovskite solar cells

An electron transport layer (ETL) is essential for charge separation and electron extraction in perovskite solar cells (PSCs). In this work, we develop an efficient electron transport layer material SnO2-PMo12 composite for the fully printable hole transport material (HTM)-free PSCs, in which PMo12 denotes the Keggin-type polyoxometalate H3PMo12O40. Benefitting from the synergistic effect of polyoxometalates, SnO2-PMo12 shows enhanced electron mobility, faster electron extraction and proper downward shift of the conduction band minimum, which boosts the injection and transfer of electrons from the perovskite to the ETL and effectively suppresses charge recombination. In addition, the hysteresis-free behavior appears in the SnO2-PMo12 device, suggesting a remarkable improvement in photovoltaic performance and device stability. Compared to the conventional TiO2 ETL, the average power conversion efficiency of the device with SnO2-PMo12 ETL is boosted from 10.1% to 12.6%. This work brings a new insight into the promoting photovoltaic performance and stability of the fully printable HTM-free PSCs. (C) 2018 Elsevier Ltd. All rights reserved.