Improved Interface Contact for Highly Stable All-Inorganic CsPbI₂Br Planar Perovskite Solar Cells

Owing to its suitable band gap and remarkable thermal stability, all-inorganic perovskite CsPbI2Br has caught the eye of academic and industry researchers recently. However, it still suffers from a phase transition due to poor stability in ambient atmosphere. Here, we introduce CsBr as an interfacial layer between the electron transport layer and the CsPbI2Br perovskite absorber layer to induce more favorable perovskite crystal growth and fabricate devices with a facile structure of ITO/SnO2/CsBr/CsPbI2Br/spiro-OMeTAD/Ag. The CsBr buffer layer plays a role in reducing the lattice mismatch, so it can not only induce and manage the formation of CsPbI2Br film but also significantly enhance the phase stability of the perovskite. After the modification, the devices demonstrate conspicuous improvement in illuminated, thermal, ambient, and long-term stabilities without any encapsulation. Meanwhile, the device performance is also improved. The unencapsulated CsBr treated device manifests illuminated stability with PCE remaining above 80% of its initial value after long-time exposure, remarkable thermal stability remaining over 78% of the initial values, better humidity resistance, and only 13% decline after being stored in N2 glovebox over 40 days.