Crosslinked thioctic acid as a multifunctional buried interface modifier for high-performance inorganic perovskite solar cells

A buried interface with desired properties plays a vital role in constructing efficient and stable perovskite solar cells (PSCs). However, the defects and energy-level mismatch generated at perovskite-transport layer interfaces severely restrict their advancement for practical applications. Herein, a cross-linkable small molecule thioctic acid (TA), which can simultaneously anchor to the surfaces of ZnO and inorganic perovskite through chemical coordination effects, is exploited as a multifunctional modifier to insert at the ZnO/perovskite buried interface for regular CsPbI2Br PSCs. After the thermal treatment, the TA molecules were not only crosslinked in situ to form a robust continuous polymer network to greatly passivate the surface defects but also ameliorate the interfacial contact and energy level alignment. Meanwhile, a high-quality CsPbI2Br film with enlarged grain size and higher crystallinity is tightly featured on the TA-modified ZnO layer. Consequently, remarkably accelerated charge extraction and suppressed charge recombination are achieved in CsPbI2Br PSCs, delivering a superior power conversion efficiency (PCE) of 16.56% with an outstanding open-circuit voltage (VOC) of 1.306 V compared to that with the control device (PCE of 14.54%, VOC of 1.188 V). Moreover, tremendous improvements in long-term and operational stability are acquired for the TA-based unencapsulated PSCs. By using crosslinkable small molecule thioctic acid (TA) as a multifunctional modifier to insert into the ZnO/perovskite buried interface, a champion efficiency of 16.56% was achieved for the CsPbI2Br PSCs with significantly improved device stability.