Stable and environmentally friendly perovskite solar cells induced by grain boundary engineering with self-assembled hydrogen-bonded porous frameworks

Abstract

Due to the unpredictable composition and vulnerable nature of the grain boundaries (GBs), grain boundaries engineering with improving the order degree of perovskite GBs would be the breakthrough for high-performance polycrystalline perovskite solar cells (PSCs). However, there are rare works on the stacking structures of passivators and on their influence on performance. Herein, based on the easily aggregate nature, a bicarbazole molecule featuring cyanogroup was used as a GB passivator to self-assemble ordered porous framework structures in GBs. The formation of pores depends on the inversion of the carbazole plane. Besides defect passivation, humidity barrier and crystallization promotion abilities, the ordered porous stacking structure shows extra advantages on lead leakage elimination and tensile stress relief. The easily deformable quadrilateral pores, which are connected by weak forces with adjustable bond length, give the skeleton a function of “turning joint” that releases tensile stresses during the thermal process by its structural expansion, and thus, restricting perovskite expansion with ion migration/evaporation suppression, which is commendable for passivators. As a result, a champion PCE of 23.15% is realized, and PSCs show significantly enhanced thermal and operational stability, as well as diminished lead leakage. This work reveals more possibilities in grain boundary engineering and provides a new avenue for stable and environmental-friendly PSCs.