Enhanced performance of GeSe thin-film solar cells via bifacial charge transport materials design

Abstract

Owing to non-toxic, earth abundant and stable properties, GeSe has become a promising photovoltaic absorber material in thin-film solar cells (TFSCs). Currently GeSe film is mainly prepared by rapid thermal sublimation (also called one-step method), where the evaporation source and substrate are heated together, thus it is difficult to regulate their temperatures independently, leading to the re-sublimation of GeSe film and diffusion of Cd element. In this work, a two-step method is introduced to prepare the GeSe film. Moreover, a synergic interface design is applied to enhance the performance of GeSe TFSCs. On one hand, the conductivity of CdS buffer layer is increased by post-annealing to reduce the series resistance and promote the electron transfer from GeSe to CdS, validated via linear sweep voltammetry curves. On the other hand, Cu2O is inserted as a hole transport layer for the first time. The Cu2O layer has sufficiently improved the hole extraction efficiency and suppressed the charge recombination, demonstrated by transient photovoltage spectroscopy and electrochemical impedance spectroscopy. By incorporating these bifacial modifications, the power-conversion efficiency (PCE) of the device has been improved by about four times (0.16%–0.63%), comparable to the highest PCE among all the reported GeSe TFSCs fabricated via a two-step method.