Thickness-insensitive polymeric hole-transporting layer for efficient inverted perovskite solar cells

Recently, inverted perovskite solar cells (PSCs) have been developed rapidly with the assistance of hole-transporting layers (HTLs), especially self-assembled monolayers (SAMs). However, present device performance strongly depends on HTL thickness, which should be strictly controlled to ∼5 nm, and >10 nm SAM HTL will induce severe efficiency loss. Here, we report a thickness-insensitive polymeric HTL (P3CT-TBB) through poly[3-(4-carboxylbutyl) thiophene] (P3CT) p-doping with 1,3,5-tris(bromomethyl)benzene (TBB). TBB can withdraw electrons from the thiophene chain in P3CT to promote its p-doping. The doped P3CT-TBB exhibits a ∼10-fold increase in film conductivity in comparison with control P3CT. As a result, P3CT-TBB-based inverted PSCs show the highest efficiency of >26% without thickness sensitiveness, and >24% efficiency remains in PSCs with over 60 nm P3CT-TBB. Besides, due to the improved hole extraction, device stability is also improved, retaining ∼90% of initial efficiency after maximum power point (MPP) tracking for 1,200 h under the ISOS-L-2 protocol (65°C).