Constructing quasi-2D perovskite to collect hot carriers to reduce open-circuit voltage loss for efficient inverted perovskite solar cells

Inverted perovskite solar cells (PSCs) have received great attention owing to the high certificated power conversion efficiency (PCE) reaching 26.7%. However, interfacial charge recombination is far superior to perovskite bulk charge recombination due to the use of fullerenes and their derivatives in inverted perovskite solar cells, which induces devastating open circuit voltage (V_OC) losses. For this reason the present work attempts to use 4-chloropiperidine hydrochloride for the upper surface modification of perovskite to construct a quasi-two-dimensional (2D) structure with suitable 2D layer widths (n=2, 3 dominant), which has a smaller electron carrier transport barrier without sacrificing short-circuit current (J_SC) in the device. This strategy effectively passivates the interfacial defect states while promoting energy level alignment to achieve carrier dissociation and equilibrium transport at the interface, which in turn resulted in improved fill factor (FF). In addition, additional energy levels are provided by 2D perovskites to collect hot carriers, resulting in improved device open circuit voltage (V_OC). As a result, the device PCE increases from 22.37% to 24.11% after the 4CPD treatment. In addition, the 4CPD-treated PSCs maintain 90% of the initial PCE after storage in an N₂ atmosphere at 50 °C for 1,080 h, whereas the control devices show a 15% PCE loss under the same aging conditions. This work provides new opportunities to suppress interfacial charge recombination in inverted devices.