Coordination engineering with crown ethers for perovskite precursor stabilization and defect passivation†

Abstract

An understanding of coordination chemistry is essential for the development of perovskite photovoltaics. By using a series of structurally similar crown ethers as the model systems, we show that coordination between Lewis base modulators and Pb²⁺ is simultaneously determined by the enthalpy effect (the electron-donating ability of the host molecule towards Pb²⁺) and entropy effect (the interaction distance between the host molecule and Pb²⁺ and the softness of the host molecule). The coordination strength of perovskite precursors is dominated by the entropy effect. The crown ether with a large ring size suppresses the formation of high-order iodoplumbates and harmful by-products such as HI and I₃⁻. The charge transfer ability of perovskite thin films is influenced by both enthalpy and entropy effects. The crown ether with a large ring size and strong electron donation characteristics exhibits the best defect passivation ability. As a result, perovskite precursors with crown ethers can be stable for up to 120 days. Perovskite solar cells demonstrate a power conversion efficiency of 25.60% (certified 25.00%) and an operational T₉₅ lifetime of 1200 hours under 1-sun equivalent illumination. This work provides generally applicable guidance on designing Lewis base modulators via coordination engineering for perovskite precursor stabilization and defect passivation.