Solution-Processed Cu₉S₅ as a Hole Transport Layer for Efficient and Stable Perovskite Solar Cells

Abstract

Organic-inorganic perovskite solar cells have seen tremendous developments in recent years. As a hole transport material, 2,2',7,7'-tetrakis( N, N-di- p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) is widely used in n-i-p perovskite solar cells. However, it may lead to the perovskite film degradation due to the dopant lithium bis((trifluoromethyl)sulfonyl)amide (Li-TFSI), which has strong hydrophilicity. CuS is considered as a superior p-type transport material, which also has a favorable energy level matching with the highest occupied molecular orbital of Spiro-OMeTAD. Herein, a solution-processed organic-inorganic-integrated hole transport layer was reported, which is composed of the undoped Spiro-OMeTAD and CuS layer. Since there is no Li-TFSI doping, it is extremely conductive to the long-term stability of the solar cells. In the meantime, we proposed a method to adjust the lowest unoccupied molecular orbital (LUMO) of SnO via nitrogen implantation (N:SnO). The LUMO of SnO can be tuned from -4.33 to -3.91 eV, which matches well with the LUMO of CHNHPbI (-3.90 eV), and thus helps to reduce hysteresis. The modified hole and electron transport layers were applied in n-i-p perovskite solar cells, which achieve a maximum power conversion efficiency (PCE) of 17.10 and 96% retention of PCE after 1200 h in air atmosphere without any encapsulation.

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

“…From the KPFM test and the reported band structure of Cu 9 S 5 , the band diagrams of Cu 9 S 5 /MoS 2 is drawn in Figure f. It can be seen that a Type‐II contact is formed between Cu 9 S 5 and MoS 2 , which facilitates the charge separation and transfer in the p‐n junction.…”

“…The optical bandgap of one nanomaterial is deeply linked with its morphology. The reported bandgap of Cu 9 S 5 varied from 1.73 eV (film) to 1.93 eV (nanocube) and 2.5 eV (bulk) . Therefore, to make clear the bandgap of the synthesized Cu 9 S 5 nanoflakes, we conducted photoluminescence (PL) and micro‐area absorption measurements on a single nanoflake.…”

“…Cu 9 S 5 ( x = 0.2), among Cu 2− x S, is a direct band gap p‐type semiconductor with good stability and high optical absorption coefficient. The high hole mobility of Cu 9 S 5 can also decrease series resistance in lateral channel, which reduces diffusion time of majority carriers and hence increase the responsivity and response rate of p‐n diodes . Nevertheless, the synthesis of Cu 9 S 5 is difficult since multiple stoichiometry and phases exist in Cu 2− x S .…”

A Review of Perovskites Solar Cell Stability

“…Han et al reported organic‐inorganic hybrid HTL which was composed of the unhoped spiro‐OMeTAD and Cu 9 S 5 layer . The modified hole and electron transport layers were applied in n–i–p perovskite solar cells.…”

High performance perovskite solar cells using Cu9S5 supraparticles incorporated hole transport layers

“…Lei et al assembled PSCs based on a doped Spiro-OMeTAD/Cu 7.5 S double layered HTM by vacuum thermal evaporation of CuS powders, reaching a PCE of 17.91% [28]. Very recently, Han et al fabricated a planar PSC with an undoped Spiro-OMeTAD/ Cu 9 S 5 double layered HTM and nitrogen doped SnO 2 ETL, achieving a maximum PCE of 17.10% [29]. Cu 9 S 5 was proven to be a superior HTL and electrode interface modification layer in both polymer and PSC solar cells [29,30].…”