Theory‐Guided Material Design Enabling High‐Performance Multifunctional Semitransparent Organic Photovoltaics without Optical Modulations

Semitransparent organic photovoltaics (ST‐OPVs) have drawn great attention for promising applications in building‐integrated photovoltaics, providing additional power generation for daily use. A previously proposed strategy, “complementary NIR absorption,” is widely applied for high‐performance ST‐OPVs. However, rational material design toward high performance has not been achieved. In this work, an external quantum efficiency (EQE) model describing this strategy is developed to explore the full potential of material design on ST‐OPV performance. Guided by the model, a novel nonfullerene acceptor (NFA), ATT‐9, is designed and synthesized, which possesses optimal bandgap for ST‐OPVs, achieving a record short‐circuit current density of 30 mA cm−2 and a power conversion efficiency of 13.40%, the highest value among devices based on NFAs with bandgaps lower than 1.2 eV. It is notworthy that, at such a low bandgap, the energy loss of the device is only 0.58 eV, which is attributed to the low energetic disorder confirmed by an ultralow Urbach energy of 21.6 meV. Benefiting from the optimal bandgap and low energy loss, the ATT‐9‐based ST‐OPV achieves a high light utilization efficiency of 3.33% without optical modulations, and meanwhile shows excellent thermal insulation, exceeding the commercial 3M heat‐insulating window film, demonstrating the outstanding application prospects of multifunctional ST‐OPVs. Detailed balance theory is applied to explore the performance potential for semitransparent organic photovoltaics (ST‐OPVs) based on complementary near‐infrared materials. With this theory, ATT‐9 with an optimal ultranarrow bandgap is designed and synthesized. The near‐infrared blend PTB7‐Th:ATT‐9 featuring an ultralow Urbach energy achieves multifunctional ST‐OPVs with an excellent light utilization efficiency and heat‐insulation performance exceeding commercial 3M films.