Abstract
The hole transport layer (HTL) is one of the main factors affecting the efficiency and stability of perovskite solar cells (PSCs). However, obtaining HTLs with the desired properties through current preparation techniques remains a challenge. In the present study, we propose a new method which can be used to achieve a double-layer HTL, by inserting a CuI layer between the perovskite layer and Spiro-OMeTAD layer via a solution spin coating process. The CuI layer deposited on the surface of the perovskite film directly covers the rough perovskite surface, covering the surface defects of the perovskite, while a layer of CuI film avoids the defects caused by Spiro-OMetad pinholes. The double-layer HTLs improve roughness and reduce charge recombination of the Spiro-OMeTAD layer, thereby resulting in superior hole extraction capabilities and faster hole mobility. The CuI/Spiro-OMeTAD double-layer HTLs-based devices were prepared in N2 gloveboxes and obtained an optimized PCE (photoelectric conversion efficiency) of 17.44%. Furthermore, their stability was improved due to the barrier effect of the inorganic CuI layer on the entry of air and moisture into the perovskite layer. The results demonstrate that another deposited CuI film is a promising method for realizing high-performance and air-stable PSCs.
Highlights
Perovskite, an organic–inorganic metal halide, which acts as a light absorber for solid film solar cells, has attracted extensive attention lately as a result of its excellent photoelectric properties, such as direct band gap, low exciton binding energy, wide light absorption spectrum range, long electron/hole diffusion length and high absorption [1,2,3,4,5,6].In just a few years, perovskite solar cell efficiency reached 25.5% [7,8]
The CuI layer deposited on the perovskite surface was annealed by solution spin coating, because liquid spin coating is a low-cost and easy to control means
The CuI layer and Spiro -OMeTAD layer produced by spin coating formed a double-layer hole transport layer
Summary
Perovskite, an organic–inorganic metal halide, which acts as a light absorber for solid film solar cells, has attracted extensive attention lately as a result of its excellent photoelectric properties, such as direct band gap, low exciton binding energy, wide light absorption spectrum range, long electron/hole diffusion length and high absorption [1,2,3,4,5,6]. CuI, CuO, CuCrO2 , NiOx, Cu2 O and CuSCN have been used as hole transporting layers to improve device stability [16,17,18,19,20,21,22,23]. Experience has shown that the Spiro-OMeTAD layer contains many holes derived from lithium bis(trifluoromethanesulfonyl)imines (LiTFSI) dopants, and these pinholes are found between the perovskite layer and the air or electrode, thereby leading to a poor stability or efficiency. CuI has long been used as a hole transport layer because of its appropriate energy level, which is very suitable for perovskite solar cells. We achieved a 17.44% PCE for double HTLs based devices, and the VOC was 1.10 V, which was 0.05 V higher than a single Spiro-OMeTAD. The stability of perovskite solar cells was further improved
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