Minimizing the buried interfacial energy loss using a fluorine-substituted small molecule for 25.92%-efficiency and stable inverted perovskite solar cells

Achieving optimal interfacial contact and band alignment at the buried interface of perovskites is crucial for minimizing the energy loss in perovskite solar cells (PSCs). Herein, a series of fluorine-substituted succinic acid derivatives are rationally introduced into the bottom interface of a perovskite. Tetrafluorosuccinic acid (TFSA), with its symmetric molecular structure and strong electronegativity, has been proven to be the best interfacial regulator among the selected functional molecules. TFSA not only effectively stabilizes FA cations via multi-site hydrogen-bonding, but also passivates under-coordinated Pb2+ defects through coordination effects. Moreover, TFSA finely regulates the morphological arrangement and homogenizes the surface contact potential of MeO-2PACz, resulting in the formation of high-quality perovskite films with reduced interfacial charge transport barriers and suppressed non-radiative recombination. Consequently, an exceptional efficiency of 25.92% (certified 25.77%) was achieved for a 0.09 cm2 inverted device, along with a voltage loss of 0.36 V and excellent long-term operational stability, representing the highest value reported for inverted PSCs based on RbCsFAMA-based perovskites to date. Additionally, a 12.96 cm2 (active area) minimodule delivers an impressive efficiency of 22.78%, demonstrating great upscaling potential. This study opens an effective strategy to rationally regulate the buried interfacial energy loss towards highly efficient and stable inverted PSCs. Tetrafluorosuccinic acid was introduced into the buried interface to stabilize FA cations, mediate crystal growth of perovskite and reduce the hole-transport barrier, delivering a record efficiency of 25.92% for RbCsFAMA-based perovskite solar cells.