Researchers at The Hong Kong Polytechnic University’s RISE and PRI have developed semitransparent organic photovoltaics (ST-OPVs) for smart window applications. The study, published in Nature Communications, introduced a new parameter, FoMLUE, to evaluate photoactive materials by combining average visual transmittance, bandgap, and current density. Among the tested materials, PBOF and eC9 achieved the highest FoMLUE values of 0.084 and 0.161. The resulting ST-OPV devices recorded a light utilization efficiency of 6.05%. They also showed enhanced thermal insulation and operational stability under varying conditions. Geographical analysis indicated that the hot summer and warm winter regions were most suitable for deployment. The optimized ST-OPV glazing achieved estimated annual energy savings of 1.43 GJ per square meter.