Nucleation Engineering to Strengthen Interface Contacts in Single‐Crystal Perovskite Photovoltaics

Perovskite solar cells (PSCs) based on single crystals hold potential for higher efficiency and stability, while the incomplete interface contact hinders hole carrier extraction and device performance. Herein, we report strengthening crystal/substrate contact by nucleation engineering based on in situ growth strategy. Through modulating the hole transport layer (HTL) to induce the nucleation process at substrate surface, interface residual solution, voids, and small-sized crystals are eliminated, thus ensuring intimate interface contact physically. Combining with strong interaction between perovskites and HTL, balanced electron/hole carrier extraction and suppressed nonradiative recombination are achieved. As a result, an impressive power conversion efficiency (PCE) of 25.8 % is obtained, setting a new efficiency benchmark for single-crystal PSCs. Moreover, the thermal-induced peeling-off of crystals from substrates is mitigated, which improves the device thermal stability distinctly.