Elimination of defect and strain by functionalized CQDs dual-engineering for all-inorganic HTMs-free perovskite solar cells with an ultrahigh voltage of 1.651 V

The high-quality perovskite film with reduced defect states and released lattice strain is crucial to the performance development of perovskite solar cells (PSCs). Herein, carbon quantum dots with bromine functional groups (Br-CQDs) are firstly synthesized and creatively employed as additive and buried interface modifier to enhance perovskite film quality. Arising from the strong anchor binding of bromine and oxygen-containing groups in Br-CQDs with uncoordinated Pb 2+ and Cs + ions within perovskite and the insertion of Br-CQDs into perovskite lattice, the incorporation of Br-CQDs exerting the role of an “adhesive” can not only effectively retard nucleation and growth processes, heal defect states and release lattice strain of perovskite film, but also regulate interfaces energy level. As a result, the charge recombination and energy loss inside PSCs are evidently suppressed thanks to the resultant high-quality perovskite film and more matching interfaces energy level. Finally, the hole-free PSC achieves an exciting PCE up to 10.79% with an ultrahigh V OC of 1.651 V, which is to date the highest efficiency and V OC for the mesoporous all-inorganic CsPbBr 3 PSCs without hole transport materials. Furthermore, the optimized PSCs display a superior long-term stability under air conditions with 85% RH at 85 °C and continuous illumination. Arising from the anchor of bromine and oxygen-containing groups in Br-CQDs with uncoordinated Pb 2+ and Cs + ions at surface and in bulk of PVK and the insertion of Br-CQDs additive in PVK lattice, the introduction of Br-CQDs like a lattice “adhesive” reduces the nucleation and growth, the trap states emergence and the tensile strain of CsPbBr 3 films, which helps the HTM-free CsPbBr 3 PSCs achieve a champion PCE up to 10.79% with an ultrahigh V OC of 1.651 V and excellent stability. • The incorporation of Br-CQDs like an “adhesive” heals defects and releases strain. • The charge recombination inside Br-CQDs tailored PSCs is effectively reduced. • Using Br-CQDs helps the HTM-free CsPbBr 3 PSCs achieve a champion PCE of 10.79%. • The unencapsulated device shows excellent tolerance toward high humidity and heat.