Progress and issues in p-i-n type perovskite solar cells

P-i-n type perovskite solar cells (PSCs) manifest some promising advantages in terms of remarkable operational stability, low-temperature processability, and compatibility for multi-junction devices, whereas relatively low efficiency compared to n-i-p type PSCs because of mismatched energy level alignment and poor interface quality at both n- and p-type contacts. Recently, great progress has been achieved in the p-i-n type PSCs, and efficiencies exceeding 25% have been reported from different research groups. Herein, state-of-the-art strategies in the deployment of high-performance p-i-n type PSCs have been systematically reviewed including engineering top-surface and buried interface of perovskite films with eliminated non-radiative charge recombination, modulating conduction types of the perovskites with well aligned energy level to facilitate charge transport, and designing effective hole transport materials for lossless charge extraction, and so on, based on which perspectives in the further design of efficient, stable and scalable p-i-n type PSCs are provided from the aspects of materials design, device fabrication, scalability and functionalization.