Solution-processed polymer bilayer heterostructures as hole-transport layers for high-performance opaque and semitransparent organic solar cells

Interfacial layer materials such as hole-transport layers (HTLs) are critical to realizing high-performance organic solar cells (OSCs). However, most OSCs are relying on a prominent HTL material of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with the hygroscopic and acidic feature, which induces poor device stability and limited power conversion efficiencies (PCEs). Here, a novel type of HTLs is developed by combining intrinsically stable poly(triarylamine) (PTAA) with modified PEDOT:PSS for efficient opaque and semitransparent OSCs with good stability. Using diluted solution processing, isopropanol-diluted PEDOT:PSS (ID-PEDOT:PSS) is deposited onto hydrophobic PTAA to improve interfacial compatibility, thereby forming a fitted polymer bilayer heterostructure HTL of PTAA/ID-PEDOT:PSS with high film quality and good transparency. For applications in OSCs with a nonfullerene acceptor (M36), the resulting opaque devices deliver an improved PCE of 14.45%, much higher than 5.72% and 13.21% for the pure PTAA and PEDOT:PSS HTLs-based devices, respectively. The stability of the PTAA/ID-PEDOT:PSS-based OSCs is improved simultaneously, where a normalized PCE for the device after storage over three months retains above 80%, much better than those of devices with other two HTLs. This novel HTL is further used to achieve efficient and stable semitransparent M36-based devices for the first time, exhibiting an outstanding PCE of 12.34% at a high average visible transmittance of 25.56%. Our findings provide an excellent semiconducting interlayer candidate to develop promising opaque and semitransparent OSCs.