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Dianyi Liu1 Chenchen Yang1 Richard Lunt1

1, Michigan State University, East Lansing, Michigan, United States

Transparent photovoltaic (TPV) technologies offer an exciting approach to produce smart windows on buildings, vehicles, mobile electronics, and greenhouses. TPVs can both regulate the transmission of solar heat and provide electricity generation by photoelectron conversion of the invisible part of the solar spectrum. While there is substantially less overall solar photon flux in the ultraviolet, efficiencies up to 7% are theoretically achievable due to high photovoltages > 2V. The approach of selectively harvesting ultraviolet-only photons can enable integration of more traditional semiconductors such as GaN, ZnO, and more enticingly halide perovskites. To date, reported ultraviolet (UV) harvesting TPV devices are still limited by low efficiency (£ 0.1% for inorganic-based devices) and/or low average visible transparency (AVT £ 60%). In this work, we develop a new platform of TPVs based on halide perovskite semiconductors where the bandgap is precisely tuned with a range of compositions to selectively harvest only UV photons with bandgaps between 400-440 nm. We will discuss the methods we developed to enable this tunability and the challenges that exist to control the morphology. Based on this insight, we demonstrate TPV devices with power conversion efficiencies (PCEs) up to 0.52%, average visible transparency (AVT) up to 70.7%, and color rendering index (CRI) over 92. These transparencies are among the highest ever reported for wavelength-selective TPVs. This approach offers theoretical efficiencies up to 7% with 100% visible transparency and CRI > 90. While these first demonstrations are limited by quantum efficiencies of only 20-30%, practical optimization of these perovskite cells could quickly yield TPVs with PCEs in the 3-5% as quantum efficiencies approach 90%. Such devices would rival state of the art TPVs that selectively harvest near-infrared light while also providing a route to higher efficiency multi-junction TPVs when synergistically coupled with near-infrared harvesting TPVs. This work ultimately creates an enticing new direction for halide perovskite research.

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