A multifunctional strategy of two-dimensional WS2 modified absorbers for efficient planar perovskite solar cells

Abstract

The development of functional absorbers with excellent film-forming quality and carrier extraction/transfer efficiency is of great significance to achieve high-efficiency and stable n–i–p planar perovskite solar cells (PSCs). Herein, we propose a simple in situ growth technique to construct high-quality absorbers by introducing a commercial two-dimensional (2D) tungsten sulfide nanosheet (WS₂ NS) modifier during the growth of a perovskite. The synergistic effects of WS₂ on perovskite crystallization kinetics, charge extraction/transfer/recombination behaviors, and device photovoltaic outputs were systematically studied. Owing to the strong coordination effect between WS₂ NSs and organic cations in a perovskite, WS₂ can be used as a growth template in the crystallization process of the perovskite, thus effectively passivating grain boundaries and surface/interface trap states, and synchronously improving the film-forming quality, surface/interface contact, and photogenerated charge extraction/transfer efficiency of the perovskite. Moreover, WS₂ located at the grain boundaries and surface/interface provides the “fast paths” for photogenerated electron–hole pairs by virtue of its high charge mobility, which greatly inhibits the accumulation/recombination of charge carriers and effectively improves the photovoltaic performance and hysteresis behavior of planar PSCs. Additionally, WS₂ NSs induce the substitutional doping of formamidinium cations, which has a positive contribution to broadening the spectral response range. The results show that the efficiency of the WS₂-modified PSC is significantly better than that of the conventional planar device. The non-encapsulated functionalized devices also exhibit good stability due to the multifunctional effects of a WS₂-modified perovskite, resulting in great advantages for the development of highly efficient flexible-, semitransparent-, and tandem-photovoltaic applications.