Metal halide perovskite is an emerging photovoltaic absorber that has garnered much attention in the photovoltaic research community in recent years. The term "perovskite" refers to any material with the same crystal structure as calcium titanate (CaTiO3), which is shown above in the blue box. While perovskites comprise a large family of materials, metal halide perovskites are a particular subset that exhibit remarkable optoelectronic properties. Specifically, the bandgap of the perovskite is direct, which allows it to efficiently absorb sunlight. For this reason, perovskite-based solar cells only require thin layers (~1 micron) of perovskite absorber material to absorb all the useable sunlight. These thin films can be deposited using scaleable and low-cost deposition techniques (orange box) such as solution-based printing methods or vapour deposition. An additional advantage of metal halide perovskites it that the bandgap can be tuned across the visible and near-infrared range by controlling the atomic composition of the material.
While most commercially available solar cells use a single absorber material, a tandem approach where two different solar absorbers are stacked on top of one another can theoretically produce even higher power conversion efficiencies. This approach works when each absorber material absorbs different colours of sunlight. As shown in the red box above, an all-perovskite tandem solar cell would use a wider bandgap top absorber that efficiently converts higher energy photons to electrical power and allows lower energy photons to pass through and be absorbed by the lower bandgap bottom absorber material. While this approach is technically more challenging, the ease of processing perovskite thin films is expected to allow the fabrication of more efficient solar cells at a still competitive cost point.
