Device physics of back-contact perovskite solar cells

Back-contact perovskite solar cells (PSCs) are a promising candidate to further increase power conversion efficiency (PCE) and have been the subject of many investigations. However their full potential has not been achieved due to a lack of a complete understanding of their operation from a device physics perspective. In this study, a detailed photoelectrical model for back-contact PSCs is developed by coupling a drift-diffusion description of a free charge transport model with ion migration currents and emitted-carrier generation resulting from photon recycling. By studying the influence of relevant electrical parameters, the interplay between charge generation, transport and recombination is revealed to further clarify the design principles based on devices with a back-contact structure. Although devices featuring the back-contact structure exhibit sensitivity to electrical parameters, a high PCE exceeding 25% is predicted if the interface passivation and perovskite film quality can be well controlled. Different conduction band and valence band offsets offering various screening opportunities for functional materials with high efficiencies are introduced. Additionally, the simulated results revealed that mobile ions degrade the device performance if the average ion concentration exceeds 1016 cm-3. Furthermore, we point out that photon recycling can effectively compensate for radiative recombination, thereby resulting in an improved open circuit voltage. The results provide a new understanding of the carrier transport dynamics, ion migration, and photon recycling effects for the back-contact structure, which can be applied for a systematic improvement in the design of high efficiency PSCs.