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 photovoltaics, including photovoltaic windows and greenhouses, has garnered significant attention. Unlike traditional inorganic materials, the unique properties of organic materials allow 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 a groundbreaking "complementary absorption of the near-infrared region" strategy using non-fullerene electron acceptors with small bandgaps. This innovation significantly enhanced the efficiency of translucent organic photovoltaics, propelling the field forward. To further optimize near-infrared spectral utilization, the research team developed a novel non-fullerene acceptor through nitrogen atom doping. This approach aligned well with widebandgap electron donors, resulting in a non-radiative energy loss of just 0.15 eV—lower than the 0.18 eV typically observed in traditional silicon cells. By incorporating this receptor 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, the ternary system-based translucent organic photovoltaic achieved a photoelectric conversion efficiency exceeding 14% at an AVT of over 20%. These findings were published in Angew. Chem. Int. Ed., highlighting the challenge of optimizing the light transmittance of wide-bandgap donor and narrow-bandgap acceptor combinations for high-performance translucent photovoltaics. Recently, the team delved into theoretical research on translucent photovoltaics, starting with fine equilibrium theory. They established an ideal EQE model based on the "complementary absorption of the near-infrared region" strategy, leading to three key insights: 1) The light utilization efficiency (LUE) of translucent photovoltaic devices is dictated by the acceptor, validating the scientific basis of this strategy; 2) The optimal bandgap for translucent organic photovoltaics is much narrower than that for conventional opaque photovoltaics; 3) Strategic material design is critical for enhancing translucent device performance. Building on these insights, the researchers designed an ultra-narrow bandgap non-fullerene acceptor leveraging the quinone resonance effect. When paired with a narrow bandgap electron donor, the photovoltaic device achieved a spectral response up to 1075 nm (1.15 eV), nearing the optimal bandgap for semi-transparent photovoltaics. This advancement enabled opaque devices to reach a record-breaking short-circuit current density of over 30 mA cm⁻² in organic photovoltaics and achieved the highest photoelectric conversion efficiency (13.32%) for non-fullerene photovoltaics above 1000 nm. Through further device optimization, the translucent device attained a photoelectric conversion efficiency of 9.37% at an AVT of 35%, setting a new LUE record of 3.33% among non-optically modified semi-transparent devices. This achievement supports cost-effective processing and the intrinsic flexibility of organic semiconductors. Additionally, the high near-infrared absorption translucent devices demonstrated excellent thermal insulation efficiency (IRR), offering thermal insulation comparable to commercial 3M thermal insulation window films at the same transmittance. These findings, illustrated in Figures 1 and 2, provide a theoretical foundation for designing highly efficient and multifunctional translucent organic photovoltaics, paving the way for innovative applications in architecture and beyond. [Figure 1: Theoretical prediction of translucent photovoltaic performance] [Figure 2: Theoretically guided "Near-infrared complementary absorption of receptor materials" strategy for efficient and multifunctional translucent organic photovoltaics]

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