Construction of multilevel network structured carbon nanofiber counter electrode and back interface engineering in all inorganic HTL-free perovskite solar cells

Carbon materials are potential counter electrodes for all-inorganic hole transport layer (HTL)-free perovskite solar cells (PSCs), whereas the defects of the perovskite/carbon back interface are the dominant reason for the low power conversion efficiency (PCE) of this kind of device. To resolve this problem, carbon nanofiber (CNF) was first synthesized using electrospinning technique to construct a carbon counter electrode with porous network architecture by self-supporting nature of CNF. The CsPbBr3 based all-inorganic HTL-free PSCs using the porous CNF counter electrode shows a PCE of 5.01%. To further modify the CsPbBr3/carbon back interface and energy level alignment, mesoporous CNF (m-CNF) and B doped m-CNF (m-BCNF) are synthesized, which can improve the conductivity of the carbon counter electrodes as well as decline the trap state densities and accelerate the carrier extraction and transport properties of the back interface. Accordingly, the all inorganic HTL-free PSCs using m-CNF and m-BCNF counter electrodes generate high PCE of 7.48% and 8.38%, with outstanding long-tern stability. The enhanced PCE improvements can be ascribe to strategies of construction of multilevel network and B doping which can modify the CsPbBr3/carbon back interface, optimize the energy level alignment of the device, and enhance the conductivity of the carbon counter electrode. This research is expected to provide meaningful support for development of new counter electrode materials and back interface engineering for high-performance all inorganic HTL-free PSCs.