Long-Range Charge Extraction in Back-Contact Perovskite Architectures via Suppressed Recombination

Metal-halide perovskites are promising solution-processable semiconductors for efficient solar cells with unexpectedly high diffusion ranges of photogenerated charges. Here, we study charge extraction and recombination in metal-halide perovskite back-contact devices, which provide a powerful experimental platform to resolve electron- or hole-only transport phenomena. We prepare polycrystalline films of perovskite semiconductors over laterally separated electron- and hole-selective materials of SnO2 and NiOx. Upon illumination, electrons (holes) generated over SnO2 (NiOx) rapidly transfer to the buried collection electrode, leaving holes (electrons) to diffuse laterally as majority carriers in the perovskite layer. Under these conditions, we find recombination is strongly suppressed. Resulting surface recombination velocities are below 2 cm s−1, approaching values of high-quality silicon. We find diffusion lengths exceed 12 μm, an order of magnitude higher than reported in vertically stacked architectures. We fabricate back-contact solar cells with short-circuit currents as high as 18.4 mA cm−2, reaching 70% external quantum efficiency.