Improving the stability and efficiency of inorganic CsPbI2Br perovskite via surface reconstruction strategy

Inorganic CsPbX3 (X = Cl, Br, I) perovskite without volatile organic components in crystal lattice, has outstanding thermal stability and broad application prospects. Various strategies have been adopted to restrain the notorious phase transition process (from cubic to orthorhombic phase) for high photoelectric conversion efficiency (PCE). Nevertheless, most studies simply focus on the surface passivation of perovskite films, ignoring the influence of surface element segregation, which is inevitable during perovskite crystallization and growth process. Herein, 2-thiopheneacetic acid (2-TPAA) was adopted to reconstruct the surface of CsPbI2Br film via secondary growth process. The constituent elements of CsPbI2Br especially Br- enrich on the surface under the action of 2-TPAA. Meanwhile, the carboxyl and thiophene groups of 2-TPAA bidentate anchor Pb2+ ions respectively, forming protective layer to inhibit the invasion of external factors. In addition, the film morphology, moisture resistance, thermodynamic stability as well as carrier transport performance of perovskite films also get improved significantly. The black phase of CsPbI2Br survives in air ambient for several days, via the synergism of surface reconstruction and passivation effect. Furthermore, the device PCE increased to 15.03%, and retained 90% initial PCE during 400 d aging. The surface reconstruction strategy provides a convenient method to improve the phase stability of CsPbI2Br perovskite films in air ambient.