Two-dimensional Bi2OS2 doping improves the performance and stability of perovskite solar cells

Abstract

• 2D Bi 2 OS 2 nanosheets are introduced as additives into the perovskite active layer. • Addition of 0.02 mg/ml 2D Bi 2 OS 2 increases power conversion efficiency (PCE) of perovskite solar cells (PVSCs). • The lifetime of optimized PVSCs is also prolonged due to addition of 2D Bi 2 OS 2 . • 2D Bi 2 OS 2 assist the formation of highly crystalline of perovskite thin film. • 2D Bi 2 OS 2 nanosheets can suppress the uncoordinated Pb 2+ ions trap states through Pb-S bond. Additive engineering has been proved to be an effective method to increase the performance of perovskite solar cells (PVSCs) by increasing the quality of the perovskite thin film. Two-dimensional (2D) Bi 2 OS 2 nanomaterial is an excellence optoelectronic material because of its tunable direct band gap, ultra-high charge mobility, wide absorption range and high absorption coefficient. In this work, 2D Bi 2 OS 2 nanosheets are synthesized and introduced as additives into the perovskite precursor solution to adjust the film formation process for the first time. Serving as heterogeneous nucleation site, 2D Bi 2 OS 2 can reduce the nucleation barrier and assist the formation of highly crystalline and crystal orientation along the (1 1 0) plane perovskite thin film, which is beneficial to improve the mobility and lifetime of charge carriers. Besides, X-ray photoelectron spectroscopy (XPS) measurement reveals that 2D Bi 2 OS 2 nanosheets can interact with Pb 2+ within the perovskite through Pb-S bond, thus suppressing the uncoordinated Pb 2+ ions trap states. Scanning electron microscope (SEM) demonstrates 2D Bi 2 OS 2 nanosheets can fill up the pin-holes and grain boundaries on the perovskite film surface. Ultraviolet photoelectron spectroscopy (UPS) measurement indicates that the valence band (VB) of optimized perovskite film is 0.28 eV upshifted closer to the highest occupied molecular orbital (HOMO) of the hole transport layer (HTL), which accelerates the charge transportation at perovskite/HTL interface. Consequently, the average power conversion efficiency (PCE) of 18.96% (highest PCE of 19.89%) is achieved upon incorporating 2D Bi 2 OS 2 nanosheets with an optimized concentration of 0.02 mg/ml into MAPbI 3 precursor solution, which is greatly improved compared to the average PCE of 15.71% for the control devices (highest PCE of 16.77%). Besides, the lifetime of optimized PVSCs is also prolonged due to the less defect states and better perovskite film quality. This work not only provides a facile method to increase the PCE and stability of PVSCs, but also reveals 2D Bi 2 OS 2 material has potential applications in PVSCs.