Recent advances in organic solar cells (OSCs) based on large-bandgap donors and low-bandgap non-fullerene acceptors (NFAs) have increased the power conversion efficiency (PCE) of OSCs to ~18%. However, these state-of-the-art OSCs have strong absorption in the visible region, limiting their application in semitransparent organic solar cells (STOSCs). In this study, an all-low-bandgap system based on a low-bandgap polymer donor (PM2) and a low-bandgap NFA (Y6-BO), was introduced as the light-harvesting layer for STOCSs with absorption mainly localized in the near-infrared (NIR) spectrum from 600 to 900 nm. The corresponding opaque OSCs exhibited the highest PCE among reported all-low-bandgap OSC systems, and the corresponding STOSCs showed higher visible light transmittances (VLTs) and light utilization efficiencies (LUEs) than the reference devices based on state-of-the-art PM6:Y6-BO OSC system with broad range absorption from visible to NIR. Optical simulations predicted that the PM2:Y6-BO-based STOSCs have a greater potential to realize higher VLTs and PCEs and better PCE retention (PCE_{semitransparent}/PCE_opaque) than those from the PM6:Y6-BO-based STOSCs. Guided by these simulations, PM2-based STOSCs with VLTs exceeding 40% and PCEs of ~6% were achieved. Further recombination analysis suggested that the PM2-based devices experienced more severe charge recombination and energy losses, indicating there is further room for PCE improvement by designing new all-low-bandgap systems. Overall, this work shows the great potential of all-low-bandgap systems in realizing STOSCs with high PCEs and VLTs, which is promising for the commercialization of OSCs as power-generating window applications.

基于大带隙供体和低带隙非富勒烯受体 (NFA) 的有机太阳能电池 (OSC) 的最新进展已将 OSC 的功率转换效率 (PCE) 提高到约 18%。然而，这些最先进的 OSC 在可见光区具有很强的吸收性，限制了它们在半透明有机太阳能电池 (STOSC) 中的应用。在这项研究中，基于低带隙聚合物供体（PM2）和低带隙 NFA（Y6-BO）的全低带隙系统被引入作为 STOCS 的光收集层，其吸收主要集中在600 至 900 nm 的近红外 (NIR) 光谱。在报告的全低带隙 OSC 系统中，相应的不透明 OSC 表现出最高的 PCE，和相应的 STOSC 显示出比基于最先进的 PM6:Y6-BO OSC 系统的参考器件更高的可见光透射率 (VLT) 和光利用效率 (LUE)，具有从可见光到 NIR 的广泛吸收范围。光学模拟预测，基于 PM2:Y6-BO 的 STOSC 有更大的潜力实现更高的 VLT 和 PCE 以及更好的 PCE 保留率 (PCE_半透明/PCE_不透明）比来自基于 PM6:Y6-BO 的 STOSC 的那些。在这些模拟的指导下，实现了 VLT 超过 40% 和 PCE 超过 6% 的基于 PM2 的 STOSC。进一步的复合分析表明，基于 PM2 的设备经历了更严重的电荷复合和能量损失，表明通过设计新的全低带隙系统还有进一步改进 PCE 的空间。总的来说，这项工作显示了全低带隙系统在实现具有高 PCE 和 VLT 的 STOSCs 方面的巨大潜力，这对于 OSCs 作为发电窗口应用的商业化是有希望的。