Enhanced efficiency and long-term stability of all inorganic CsPbBr3 perovskite solar cells via regulation of charge separation and extraction by band engineered-Co3O4 nanocrystals as a hole transport material layer

Abstract

Insertion of an inorganic HTM intermediate at the CsPbBr3/Carbon interface can significantly improve photo-generated holes extraction efficiency without sacrificing advantages in device stability. Herein, low-cost and eco-friendly Co3O4 nanocrystals were synthesized by precipitation method and utilized as efficient inorganic HTM for CsPbBr3 PSCs. By regulating the hole quasi-fermi level (Ef, HTL) of the perovskite film with Co3O4 nanocrystals possessing a lower conduction band (CB), the built-in electric field (BEF) inside the CsPbBr3 can be reinforced, for which the Co3O4-induced energy level reconstruction facilitates fast charge separation and extraction because of the intensified driving force. In addition, the charge recombination behavior can be effectively inhibited. Finally, all inorganic CsPbBr3 PSCs with an architecture of FTO/c-TiO2/m-TiO2/CsPbBr3/Co3O4/carbon PSC realizes efficiency of 8.92% with an open-circuit voltage (Voc) of 1.531 V. Furthermore, the unencapsulated Co3O4-based PSC exhibits excellent stability in ambient air, keeping 98% of its initial efficiency after 90 days in 80% high humidity condition, and 97% of initial efficiency after 40 days in a high-temperature atmosphere of ∼80 °C.