Progress in the research of high-efficiency, multifunctional translucent organic photovoltaics in the Institute of Chemistry

The integration of translucent organic photovoltaics (ST-OPVs) into architectural designs like photovoltaic windows and greenhouses has garnered significant attention. Unlike traditional inorganic materials, the unique properties of organic materials enable ST-OPVs to selectively utilize the solar spectrum, balancing both photoelectric conversion efficiency (PCE) and average visible light transmittance (AVT). In 2016, Dr. Zhu Xiaozhang from the Institute of Chemistry Research at the Chinese Academy of Sciences introduced the concept of "complementary absorption in the near-infrared region" for acceptor materials, leading to the development of efficient translucent organic photovoltaics based on small bandgap non-fullerene electron acceptors. These advancements significantly propelled the field forward, as seen in studies published in *Advanced Materials* (2017, 29, 1606574) and *Journal of the American Chemical Society* (2020, 142, 11613). To further enhance near-infrared spectral utilization, the team created a non-fullerene acceptor via nitrogen atom doping, aligning it with a widebandgap electron donor. This binary system achieved a non-radiative energy loss of just 0.15 eV, surpassing the 0.18 eV typical of traditional silicon cells. By incorporating this acceptor as the third component in a high-efficiency material combination, the team achieved complementary near-infrared absorption, boosting short-circuit current density without sacrificing open-circuit voltage. For the first time, this ternary system-based translucent organic photovoltaic reached over 14% photoelectric conversion efficiency at more than 20% AVT. These findings were published in *Angewandte Chemie International Edition*. However, the study also highlighted the limitations of current material combinations, particularly the low light transmittance and difficulty in regulation. Recently, the team delved into theoretical research on translucent photovoltaics, starting with fine equilibrium theory. They established an ideal EQE model emphasizing the "complementary absorption in the near-infrared region" of the acceptor, reaching three key conclusions: 1) The light utilization efficiency (LUE = PCE × AVT) of translucent photovoltaic devices is primarily determined by the acceptor, validating the scientific rationale behind the "near-infrared complementary absorption" strategy; 2) The optimal bandgap for translucent organic photovoltaics is significantly smaller than that of conventional opaque photovoltaics; 3) Material design plays a pivotal role in enhancing device performance. Building on these insights, the team designed an ultra-narrow bandgap non-fullerene acceptor using the quinone resonance effect. When paired with a narrow bandgap electron donor, the photovoltaic device's spectral response extended to 1075 nm (1.15 eV), nearing the optimal bandgap for semi-transparent photovoltaics. Thanks to the expanded near-infrared absorption, opaque devices achieved the highest short-circuit current density (over 30 mA cm⁻²) in organic photovoltaics and set a record of 13.32% photoelectric conversion efficiency for non-fullerene photovoltaics above 1000 nm. After optimization, the translucent device reached 9.37% photoelectric conversion efficiency at 35% AVT, achieving a LUE of 3.33%, the highest among non-optically modified semi-transparent devices. This combination supports cost-effective processing and the intrinsic flexibility of organic semiconductors. Additionally, these highly near-infrared-absorbing translucent devices demonstrated excellent thermal insulation efficiency (IRR), offering the same insulation benefits as commercial 3M thermal insulation window films while generating electricity. These findings, published in *Advanced Materials*, showcase the potential of theoretical guidance in advancing translucent organic photovoltaics toward practical applications.  **Figure 1:** Theoretical prediction of translucent photovoltaic performance  **Figure 2:** Theoretically guided "near-infrared complementary absorption" strategy for efficient and multifunctional translucent organic photovoltaics

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