The integration of translucent organic photovoltaics (ST-OPVs) into architectural applications like photovoltaic windows and greenhouses has garnered significant interest. Unlike traditional inorganic materials, organic materials allow for structured light absorption, enabling ST-OPVs to selectively utilize the solar spectrum, balancing both photoelectric conversion efficiency (PCE) and average visible light transmittance (AVT).
In 2016, Xiaozhang Zhu, a researcher at the Institute of Chemistry Research under the Chinese Academy of Sciences, introduced the "complementary absorption of the near-infrared region of the acceptor material" strategy, advancing the field of translucent organic photovoltaics. This breakthrough was published in journals such as *Advanced Materials* and *Journal of the American Chemical Society*.
To enhance near-infrared spectral utilization, the team engineered a non-fullerene acceptor using nitrogen atom doping. When combined with a widebandgap electron donor, this approach achieved a non-radiative energy loss of just 0.15 eV, significantly lower than the 0.18 eV typical of traditional silicon cells. By incorporating this receptor as a third component, the team achieved complementary near-infrared absorption, boosting short-circuit current density without sacrificing open circuit voltage. This ternary system achieved over 14% photoelectric conversion efficiency at more than 20% AVT. These findings were published in *Angewandte Chemie International Edition*. However, the study noted that the light transmittance of widebandgap donor and narrowbandgap acceptor combinations remains low and difficult to optimize, posing a challenge for high-performance translucent photovoltaics.
Recently, the team conducted theoretical research on translucent photovoltaics. Drawing from fine equilibrium theory, they established an ideal EQE model for "complementary near-infrared absorption of the receptor," leading to three key insights: 1) Translucent photovoltaic device light utilization efficiency (LUE = PCE × AVT) depends on the receptor, validating the "complementary near-infrared absorption" strategy; 2) The optimal bandgap for translucent organic photovoltaics is much smaller than for conventional opaque photovoltaics; 3) Material design plays a pivotal role in enhancing device performance. Based on these findings, the team designed an ultra-narrow bandgap non-fullerene acceptor via the quinone resonance effect. This acceptor, when paired with a narrowbandgap electron donor, achieved a spectral response up to 1075 nm (1.15 eV), approaching the optimal bandgap for semi-transparent photovoltaics. Thanks to enhanced near-infrared absorption, opaque devices reached record-breaking short-circuit current densities of over 30 mA cmâ»Â² in organic photovoltaics and a maximum photoelectric conversion efficiency of 13.32% for non-fullerene photovoltaics above 1000 nm. After optimization, the translucent device attained 9.37% photoelectric conversion efficiency at 35% AVT, yielding a LUE of 3.33%, the highest among non-optically modified semi-transparent devices. This design supports low-cost processing and intrinsic flexibility, key advantages of organic semiconductors. Additionally, these devices exhibit excellent thermal insulation efficiency (IRR), offering thermal performance comparable to commercial 3M thermal insulation window films at the same transmittance.
These developments are detailed in *Advanced Materials*, with accompanying figures illustrating the theoretical predictions and strategies guiding the creation of efficient, multifunctional translucent organic photovoltaics.
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