Point contacts in halide perovskite solar cells: from reduced interfacial recombination to increased ionic field screening

Abstract

The performance of p–i–n structured perovskite solar cells (PSCs) is primarily limited by the charge recombination at the interface between the perovskite and the electron transporting layer, most commonly C₆₀. Inspired by the silicon passivated emitter rear cell design, we propose point contacts (PCs) to reduce the recombination at the perovskite/C₆₀ interface. Inserting PCs between the perovskite and C₆₀ layers enables an increased efficiency from 18.9% to 20.0%, which mainly originates from the reduced non-radiative recombination that leads to a higher open-circuit voltage (V_OC) from 1.16 to 1.21 V. Combining a lithium fluoride (LiF) layer beneath the PCs (perovskite/LiF/PCs) can further boost the V_OC to 1.26 V, reaching 90% of the detailed balance limit. However, we find that PCs exacerbate the effect of mobile ions in PSCs, accelerating the degradation under operando conditions. Our results reveal that mobile ions accumulate at the PCs, triggering a faster degradation of the device. These observations are further supported by one- and two-dimensional drift-diffusion simulations that confirm the accumulation of ions at the PCs. This work, therefore, highlights the importance of ion management for improved stability and points to a new degradation mechanism when a discontinuous insulating layer forms at the perovskite interfaces.