Face-on Oriented Self-Assembled Molecules with Enhanced π-π Stacking for Highly Efficient Inverted Perovskite Solar Cells on Rough FTO Substrate

Abstract

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. Here, we report an asymmetric SAM, 4PABCz, by introducing additional conjugated groups to the carbazole unit of 4PACz. The 4PABCz molecules exhibit strengthened intermolecular π-π interactions and 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 4PABCz-covered substrates effectively regulates the crystallization of perovskite films and releases residual stress. As a result, the inverted PSCs on FTO substrates achieve 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 1,000 h of maximum power point tracking under ISOS-L-2 protocol. Furthermore, by incorporating 4PABCz into small-area and large-area (1.028 cm2) PET/ITO-based flexible PSCs, we obtain impressive PCEs of 24.42% (certified 24.00%) and 22.52% (certified 22.42%), respectively, demonstrating the universe applicability of our strategy.