Low-temperature processed cross-linkable hole transport layer for efficient and stable perovskite solar cells

To the best of our knowledge, poor environment stability is the main challenge for perovskite solar cells (PSCs). In this study, cross-linked hole transport layer (HTL) is built on perovskite crystal to guarantee the operation stability of mesoporous PSCs for the first time. Here, N,N'-di-p-tolyl-N,-N'-bis(4-vinylphenyl)-[1,1′-biphenyl]-4,4′-diamine (V-p-TPD) was applied as a hole-transportable polymerizable monomer with the assistance of ultraviolet photoinitiator 4-octyloxydiphenyliodonium hexafluoroantimonate (OPPI). Cross-linking process is conducted at a distinctly low temperature of only 100 °C by adjusting the V-p-TPD: OPPI ratio to 10:1, which is tolerable for the active black phase of perovskite. The resultant cross-linked V-p-TPD film is qualified with a high cross-linking degree of 99%, a high hole mobility of 3.84 × 10−4 cm2V−1s−1 and a hydrophobic surface with wetting angle of 94.6°. Mesoporous PSCs based on the obtained cross-linked HTL achieved a tremendous Power conversion efficiency (PCE) of 18.49%, which represents the state-of-the-art records of mesoporous PSCs with cross-linkable HTL. PCE of the unpackaged device can remain 88% of the initial value after 30 d in an atmospheric environment with a relative humidity of 60 ± 5%, and maintain 86% of the initial PCE after 200 h in 65 ± 2 °C argon atmosphere. This work presents a low-temperature processing strategy for the preparation of cross-linked HTL layer, which does favor to the stable and efficient energy harvesting application.