Synergistic potentiation between P3HT and PTAA enables blade-coated carbon-electrode perovskite solar cells with >21% outdoor and >35% indoor efficiencies

P3HT is a promising hole-transport layer (HTL) for efficient and stable carbon electrode-based perovskite solar cells (C-PSCs). However, the reported low efficiencies of P3HT C-PSCs, resulting from the unmatched band alignment and electronically poor contact between perovskite and P3HT, is an obstacle. In this work, we propose a binary HTL system that incorporates PTAA into P3HT to address this issue, thereby achieving efficiencies of 21.3 % (0.04 cm 2 ) and 18.8 % (1.0 cm 2 ) under AM 1.5G illumination, and 35.2 % under indoor illumination of 1000 lx, all of which are the highest reported values for low-temperature printable C-PSCs. Experimental and theoretical results revealed that the performance improvements mainly stem from the following collaborative effects between P3HT and PTAA: 1) the introduction of PTAA increases more face-on orientations of P3HT as well as enhanced π–π stacking, forming more effective charge transport channels as molecular bridges; 2) the hole extraction barrier from perovskite to P3HT is reduced by 0.07 eV through incorporating PTAA; 3) triarylamine PTAA and other more face-on configurations can provide additional and stronger passivation sites, intensifying the defect passivation effects. Finally, unencapsulated P3HT-PTAA C-PSCs maintain ≈91 % of initial performance after maximum power point tracking for over 900 h.