The key discovery consists in the observation that the composite thin film--barely 110 nanometres thick--absorbs a broader portion of the solar spectrum compared to the wavelengths absorbed in the thin films made of the two individual materials. The interfaces between the two different phases within the composite film play a crucial role in converting more sunlight into electricity. This is a surprising, novel phenomenon in the field of inorganic perovskite oxide-based solar cells. The composite material leads to a power conversion efficiency of up to 4.2%, which is a record value for this class of materials.
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