Solution-Processable 2D α-In2Se3 as an Efficient Hole Transport Layer for High-Performance and Stable Polymer Solar Cells

Herein, a 2D alpha-In2Se3 nanosheet, a binary III-VI group compound semiconductor, is fabricated by liquid-phase exfoliation method, and the photoelectric properties of alpha-In2Se3 material are investigated in depth. It is found that alpha-In2Se3 film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, alpha-In2Se3 film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D alpha-In2Se3 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/alpha-In2Se3/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 alpha-In2Se3 film possesses excellent thermal stability in the range from room temperature to 280 degrees C, and a PCE of 9.35% is achieved without annealing treatment of alpha-In2Se3 film, which exhibits a great potential of alpha-In2Se3 for an annealing-free approach. Furthermore, the incorporation of alpha-In2Se3 HTL also remarkably enhances the long-term stability of PSCs compared with PEDOT:PSS-based devices. So, the results show that 2D alpha-In2Se3 is a promising candidate to be an efficient and stable hole-extraction layer.