Buried Interface Engineering with Starburst-Shaped Self-Assembled Monolayer Enhances Efficiency and Stability of Tin Perovskite Solar Cells
Tin-based perovskite solar cells (TPSCs) are the leading candidate for lead-free perovskite photovoltaics, yet their efficiency lags behind lead-based counterparts due to interfacial losses. This highlight analyzes a recent breakthrough by Li et al. (Nature Publishing Group, 2025) that addresses these losses via a triphenylamine-based starburst-shaped D-D-p-A self-assembled monolayer (SAM) molecule, MBP, anchored on nickel oxide (NiOx) as a buried hole-transport layer. The MBP molecule features a cyanoethyl phosphate anchoring group, enabling homogeneous adsorption on NiOx, and an expanded conjugated structure that yields a highest occupied molecular orbital (HOMO) level of -4.95 eV, closely matching the valence band maximum of tin perovskites. This alignment reduces energy mismatch, while the push-pull electron system enhances hole extraction. Time-resolved photoluminescence (TRPL) and steady-state photoluminescence (PL) measurements confirm faster hole extraction and reduced non-radiative recombination at the NiOx/MBP interface. Contact angle measurements demonstrate super-wettability of the perovskite precursor on NiOx/MBP, promoting high-quality film growth. Devices incorporating NiOx/MBP achieve a champion power conversion efficiency (PCE) of 17.6% (as reported in the original paper), with significantly improved long-term shelf stability and operational stability under illumination. This work underscores the potential of tailored SAM molecules to overcome energy-level and wettability bottlenecks, advancing TPSCs toward practical application.