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

Metal-halide perovskites are promising solution-processable semiconductors for efficient solar cells and show 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 thin films of perovskite semiconductors over laterally-separated electron- and hole-selective materials of SnO¬2 and NiOx, respectively. Upon illumination, electrons (holes) generated over SnO¬2 (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, an order of magnitude lower than in the presence of both carrier types, and approaching values of high-quality silicon. We find diffusion lengths of electrons and holes exceed 12 µm in our horizontal polycrystalline device, 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

Controlling crystallization to imprint nanophotonic structures into halide perovskites using soft lithography

Halide perovskites have recently gained widespread attention for their high efficiencies in photovoltaics, and they have also been studied for applications in light emission. Both of these fields can benefit from nanophotonic patterning. Here, by controlling the crystallization of the perovskite film in contact with a nanotextured silicone polymer stamp, nanostructures are reproduced in the perovskite. Soft lithography techniques such as this imprinting are particularly useful for halide perovskites, which are incompatible with the aqueous solutions and plasmas used in conventional patterning processes. Additionally, soft lithography can pattern over defects and avoids damaging the master. By extending nanoscale soft lithography to halide perovskites, new opportunities arise in merging nanophotonics with these remarkable materials

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. Metal-halide perovskites are promising sustainable low-cost materials for optoelectronic devices such as solar cells and LEDs. To optimize performance in these applications, a detailed understanding of charge transport characteristics and the influence of interfaces, such as grain boundaries, is vital. At present, a wide range of transport parameters have been reported, often via indirect measurements, since direct measurement has proven challenging. Here, we demonstrate an approach based on measurements in a back-contact geometry that is capable of probing electron and hole transport mechanisms separately. Such insights are not typically accessible in vertical architectures. We demonstrate a back-contact perovskite device, which we find to operate by majority-carrier diffusion and find that charges diffuse remarkable distances in such scenarios. Diffusion over remarkably long distances over electron-extraction electrodes enables efficient charge collection in short-circuit conditions. A detailed understanding of charge transport is vital to maximize the efficiencies of optoelectronic devices. Using a back-contact architecture, the authors probe transport of electrons and holes separately in polycrystalline hybrid perovskite thin films. Isolating photoexcited charge carriers in separate regions of the device leads to long diffusion ranges of carriers. The authors demonstrate a back-contact perovskite solar cell that operates on majority-carrier diffusion. These results highlight electrode interfaces as limiting aspects of current back-contact architectures, indicating opportunities for improvement