NbSe2 nanosheets improved the buried interface for perovskite solar cells

Abstract

Organic-inorganic metal halide perovskite solar cells (PSCs) are favorable candidates for next-generation solar cells, due to their excellent photovoltaic performance and promising low-cost fabrication process. Particularly, tin oxide (SnO₂), with excellent charge mobility and extraction efficiency, is widely used as electron transport layers (ETLs), and the efficiency of the corresponding n-i-p-type perovskites has been certified as high as 26.21 ​% in single-junction devices. The SnO₂ layer serves as the substrate for the growth of perovskite films, determining the crystalline quality and the buried interface of perovskite films. However, due to the different thermal expansion coefficient of SnO₂ and perovskite, the subsequent perovskite annealing process leads to the residual stress at the buried interfaces and lattice distortion in the perovskite films, which seriously affects their optoelectronic performance and stability. To release this interfacial stress, researchers have made some progress by applying different polymers and small molecules to the SnO₂/perovskite interface as a buffer layer. Among these, two-dimensional (2D) nanosheets with high carrier mobility, a wide bandgap range, and excellent optical absorption properties are promising, especially 2D NbSe₂ nanosheets showing the advantages of solution-processability, high intrinsic conductivity and clean smooth surface, namely without dangling bonded atoms. Herein, 2D NbSe₂ nanosheets have been introduced at the SnO₂/perovskite interface to release the undesired residual tensile strain in perovskite films and to form a more matched interfacial energy level alignment. As a result, we have obtained a high-quality perovskite film and further an improved photovoltaic performance. The PCE has been increased from 21.81 ​% to 24.05 ​%. The unencapsulated cell maintained 91 ​% of the initial efficiency after aging over 1000 ​h under atmospheric condition.