High Light‐Utilization‐Efficiency Organic Photovoltaic Windows with Over 40% Transmittance Enabled by a Printable Bionic Photonic Reflector

Semitransparent organic solar cells (ST‐OSCs) have promising applications in building materials, automobiles, and green windows. However, photovoltaic building materials have a requirement for transmittance, which only reaches over 40% and can satisfy the condition of energy saving. In this work, a printable bionic photonic reflector is introduced to overcome the insufficient light utilization efficiency (LUE) of ST‐OSCs. The inverse‐opal photonic crystal reflectors can enhance the secondary absorption of the active layer by adjusting the particle size to reflect the wavelength of light, which can match with the absorption of the donor. Meanwhile, it allows other wavelengths of sunlight to be passed through for transmittance. With this strategy, power conversion efficiency (PCE) and average visible transmittance (AVT) are simultaneously improved. As a result, the PCE is improved to 9.93% with an AVT of 40.36%, and the LUE is significantly improved from 3.63% to 4.01%, which is a great advance in the performance of ST‐OSCs reported.