A Bi2Te3 Topological Insulator as a New and Outstanding Counter Electrode Material for High-Efficiency and Endurable Flexible Perovskite Solar Cells.

Inverted flexible perovskite solar cells (PSCs) typically employ expensive metals as the counter electrodes, which are brittle and corrodible by perovskite, leading to a sharp performance drop under continuous bending, air exposure, thermal stress, or light illumination and eventually retard the commercialization. Herein, a low-cost Bi2Te3 counter electrode was employed by using a simple thermal evaporation process. The resultant device achieved an excellent power conversion efficiency of 18.16%, which was among the highest reported efficiencies, much higher than the reference Ag PSC (15.90%). The improvement should be attributed to the intrinsic suppressed electron backscattering in a Bi2Te3 topological insulator. Simultaneously, the Bi2Te3 device obtained a significantly improved mechanical flexibility and long-term operational stability. The present strategy will help to open up a new avenue for future commercialization of flexible photovoltaic applications.