Solution‐Processable 2D α‐In 2 Se 3 as an Efficient Hole Transport Layer for High‐Performance and Stable Polymer Solar Cells

Herein, a 2D α‐In 2 Se 3 nanosheet, a binary III–VI group compound semiconductor, is fabricated by liquid‐phase exfoliation method, and the photoelectric properties of α‐In 2 Se 3 material are investigated in depth. It is found that α‐In 2 Se 3 film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, α‐In 2 Se 3 film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D α‐In 2 Se 3 nanosheet is used as a hole transport layer (HTL) in conventional PSCs for the first time, and a relatively high power conversion efficiency (PCE) of 9.58% is achieved with the structure of ITO/α‐In 2 Se 3 /PBDB‐T:ITIC/Ca/Al, which is comparable with poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices (9.50%). Interestingly, it is demonstrated that the α‐In 2 Se 3 film possesses excellent thermal stability in the range from room temperature to 280 °C, and a PCE of 9.35% is achieved without annealing treatment of α‐In 2 Se 3 film, which exhibits a great potential of α‐In 2 Se 3 for an annealing‐free approach. Furthermore, the incorporation of α‐In 2 Se 3 HTL also remarkably enhances the long‐term stability of PSCs compared with PEDOT:PSS‐based devices. So, the results show that 2D α‐In 2 Se 3 is a promising candidate to be an efficient and stable hole‐extraction layer.