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

Insertion of an inorganic HTM intermediate at the CsPbBr 3 /Carbon interface can significantly improve photo-generated holes extraction efficiency without sacrificing advantages in device stability. Herein, low-cost and eco-friendly Co 3 O 4 nanocrystals were synthesized by precipitation method and utilized as efficient inorganic HTM for CsPbBr 3 PSCs . By regulating the hole quasi-fermi level (E f, HTL ) of the perovskite film with Co 3 O 4 nanocrystals possessing a lower conduction band (CB), the built-in electric field (BEF) inside the CsPbBr 3 can be reinforced, for which the Co 3 O 4 -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 CsPbBr 3 PSCs with an architecture of FTO/ c -TiO 2 / m -TiO 2 /CsPbBr 3 /Co 3 O 4 /carbon PSC realizes efficiency of 8.92% with an open-circuit voltage ( V oc ) of 1.531 V. Furthermore, the unencapsulated Co 3 O 4 -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.