UV- and NIR-Protective Semitransparent Smart Windows Based on Metal Halide Solar Cells

In this study, a solution-processable lead iodide semiconductor having a wide band gap was investigated as a light absorbing material for various organic electron transport materials, in a search for low-cost semiconductor materials allowing the facile fabrication of efficient photovoltaic devices. A Tauc plot suggested a wide intrinsic optical band gap of 2.4 eV for a thin film of PbI2, while X-ray diffraction revealed that the spin-coated PbI2 thin film had a hexagonal crystalline structure with preferable orientation along the (001) plane. The effect of the light intensity on the values of Voc and Jsc was studied to investigate the charge recombination mechanism of fabricated devices. An efficient bifacial solar cell was prepared featuring a thin Ag film sandwiched between BCP and MoO3 layers as a transparent rear electrode. The whole device featuring the BCP/Ag/MoO3 electrode exhibited a maximum transmittance of approximately 60% in the visible region, less than 15% in the UV region, and less than 25% in the NIR region. A power conversion efficiency of 2.19% was achieved for a device featuring an opaque electrode (Ca/Al), while the corresponding device featuring the transparent electrode (BCP/Ag/MoO3) provided values of 0.75% and 0.67% when illuminated from the front and rear, respectively. Thus, wide band gap metal halide materials potentially open up a new path for fabricating efficient and transparent photovoltaic devices having applications as building-integrated smart windows. It also effectively prevents the penetration of UV and NIR light, which is harmful for human health, into the building.