Manipulating Molecular Stacking for Semitransparent Organic Photovoltaics Achieving Light Utilization Efficiency >6%

Abstract The trade‐off between average visible transmittance (AVT) and power conversion efficiency (PCE), governed by the molecular stacking of the donor and acceptor materials in semitransparent organic solar cells (ST‐OSCs), significantly constrains improvements in light utilization efficiency (LUE). Here, simultaneous enhancement of AVT and PCE is achieved by meticulously designing host‐guest active layers to fine‐tune the molecular stacking. A systematic investigation of various host donor and guest material combinations reveals that the donor material (D18) with more electron‐deficient hydrogen atoms tends to form C─H···O interactions with the guest material (BTO‐BO) that features electron‐rich oxygen atoms. Hydrogen bonding interactions between host donor D18 and guest BTO‐BO facilitate the transition from mixed J‐type and H‐type molecular stacking modes of the donor to predominant J‐type stacking during crystallization, significantly reducing visible absorption and enhancing hole transport. Additionally, BTO‐BO can act as a nucleation agent for the host acceptor BTP‐eC9 to increase the crystallinity and absorption coefficient of the active layer, thereby, enhancing near‐infrared light absorption. The resultant toluene‐processed ST‐OSCs with optical modulation exhibit simultaneous improvement in PCE and AVT, delivering record LUEs of 6.02%. Notably, this host‐guest active layer demonstrates exceptional compatibility with flexible devices and promising scalability for greenhouse photovoltaic applications.