Boosting the Performances of Semitransparent Organic Photovoltaics via Synergetic Near-Infrared Light Management

Semitransparent organic photovoltaics (ST-OPVs) offer promising prospects for application in building-integrated photovoltaic systems and greenhouses, but further improvement of their performance faces a delicate trade-off between the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT). Herein, the authors take advantage of coupling plasmonics with the optical design of ST-OPVs to enhance near-infrared absorption and hence simultaneously improve efficiency and visible transparency to the maximum extent. By integrating core-bishell PdCu@Au@SiO2 nanotripods that act as optically isotropic Lambertian sources with near-infrared-customized localized surface plasmon resonance in an optimal ternary PM6:BTP-eC9:L8-BO-based ST-OPV, it is shown that their interplay with a multilayer optical coupling layer, consisting of ZnS(130 nm)/Na3AlF6(60 nm)/WO3(100 nm)/LaF3(50 nm) identified from high-throughput optical screening, leads to a record-high PCE of 16.14% (certified as 15.90%) along with an excellent AVT of 33.02%. The strong enhancement of the light utilization efficiency by ≈50% as compared to the counterpart device without optical engineering provides an encouraging and universal pathway for promoting breakthroughs in ST-OPVs from meticulous optical design.

Semitransparent Organic Solar Cells with Homogeneous Transmission and Colorful Reflection Enabled by an ITO-Free Microcavity Architecture

Semitransparent organic photovoltaics (ST-OPVs), owing to the merits of high power generation, thermal insulation, and aesthetic features, have become a promising candidate for intellectual building- integrated photovoltaic windows. However, the traditional optical evaluation only focuses on the transmission properties and ignores the reflection behaviors. And the lack of quantitative descriptions for array appearance hinders implementation of ST-OPV based large-area modules. To tackle with these issues, an indium tin oxide (ITO)-free optical microcavity architecture into ST-OPVs for achieving high homogeneity in transmittance with controllable reflective appearances through tunning the thickness of individual component layers is introduced. A set of parameters based on optical characteristics of sub-units to provide a quantitative description for the transmittance brightness, transmissive and reflective color purity, and versatility of optical arrays, is further proposed. The optical simulations reveal that reflection modulation from blue to red colors can be realized for devices based on various bulk-heterojunction material systems through regulating the thickness of active layers and antireflection coatings. This work offers a viable design strategy for ST-OPVs toward applications in next-generation smart photovoltaic windows.

Balancing the Selective Absorption and Photon-to-Electron Conversion for Semitransparent Organic Photovoltaics with 5.0% Light-Utilization Efficiency

Efficiently converting invisible light while allowing full visible light transmission is key to achieving high-performance semitransparent organic photovoltaics (ST-OPVs). Here, a detailed balance strategy is explored to optimize the ST-OPV via taking both absorption and carrier dynamics into consideration. Based on this principle, comprehensive optimizations are carried out, including a ternary strategy, donor:acceptor blend ratio, thickness, antireflection, etc., to compromise the invisible energy conversion and visible transmission for high-performance ST-OPVs. As a result, the opaque OPV device exhibits a champion power conversion efficiency of 19.35% (certificated 19.07%), and most strikingly, the best ST-OPV shows a remarkably high light-utilization efficiency of 5.0%, where the efficiency and the average visible transmission are 12.95% and 38.67%, respectively. An efficiency of 12.09% is achieved on the upscaled device with an area of 1.05 cm² , demonstrating its promise for large-area fabrication. These results are among the best values for ST-OPVs. Besides, it is demonstrated that the ST-OPV exhibits good infrared light-reflection capability for thermal control. This work provides a rational design of balancing the absorbing selectivity and photon-to-electron conversion for high-performance ST-OPVs, and may pave the way toward the practical application of solar windows.

Theory-Guided Material Design Enabling High-Performance Multifunctional Semitransparent Organic Photovoltaics without Optical Modulations

Semitransparent organic photovoltaics (ST-OPVs) have drawn great attention for promising applications in building-integrated photovoltaics, providing additional power generation for daily use. A previously proposed strategy, "complementary NIR absorption," is widely applied for high-performance ST-OPVs. However, rational material design toward high performance has not been achieved. In this work, an external quantum efficiency (EQE) model describing this strategy is developed to explore the full potential of material design on ST-OPV performance. Guided by the model, a novel nonfullerene acceptor (NFA), ATT-9, is designed and synthesized, which possesses optimal bandgap for ST-OPVs, achieving a record short-circuit current density of 30 mA cm^-2 and a power conversion efficiency of 13.40%, the highest value among devices based on NFAs with bandgaps lower than 1.2 eV. It is notworthy that, at such a low bandgap, the energy loss of the device is only 0.58 eV, which is attributed to the low energetic disorder confirmed by an ultralow Urbach energy of 21.6 meV. Benefiting from the optimal bandgap and low energy loss, the ATT-9-based ST-OPV achieves a high light utilization efficiency of 3.33% without optical modulations, and meanwhile shows excellent thermal insulation, exceeding the commercial 3M heat-insulating window film, demonstrating the outstanding application prospects of multifunctional ST-OPVs.

Self-Supplied Nano-Fusing and Transferring Metal Nanostructures via Surface Oxide Reduction

Here, we demonstrate that chemical reduction of oxide layers on metal nanostructures fuses junctions at nanoscale to improve the opto-electrical performance, and to ensure environmental stability of the interconnected nanonetwork. In addition, the reducing reaction lowers the adhesion force between metal nanostructures and substrates, facilitating the detachment of them from substrates. Detached metal nanonetworks can be easily floated on water and transferred onto various substrates including hydrophobic, floppy, and curved surfaces. Utilizing the detached metal nanostructures, semitransparent organic photovoltaics is fabricated, presenting the applicability of proposed reduction treatment in the device applications.