Face-on oriented self-assembled molecules with enhanced π–π stacking for highly efficient inverted perovskite solar cells on rough FTO substrates†

Self-assembled molecules (SAMs) as hole transport layers (HTLs) on light-managing textured substrates promise great commercial potential for high-efficiency inverted perovskite solar cells (PSCs). However, the inhomogeneous distribution and disordered packing of SAMs on rough substrates aggravate interfacial energy loss, impeding further improvement in the efficiency and stability of PSCs. Herein, we report an asymmetric SAM, 4PABCz, developed by introducing additional conjugated groups into the carbazole unit of 4PACz. The 4PABCz molecules exhibited strong intermolecular π–π interactions and an out-of-plane dipole, enabling the formation of tightly assembled and face-on oriented HTLs to achieve dense coverage and facilitated hole extraction on substrates. Moreover, the unique configuration of the 4PABCz-covered substrates effectively regulated the crystallization of perovskite films and released residual stress. As a result, the inverted PSCs on FTO substrates achieved a champion power conversion efficiency (PCE) of 26.90% (certified 26.81% for reverse-scan and 25.96% for steady-state), retaining 93.98% of their initial efficiency after 1000 h of maximum power point tracking under the ISOS-L-2 protocol. Furthermore, by incorporating 4PABCz into small-area and large-area (1.028 cm²) PET/ITO-based flexible PSCs, we obtained impressive PCEs of 24.42% (certified 24.00%) and 22.52% (certified 22.42%), respectively, demonstrating the universal applicability of our strategy.