Optically asymmetric down-shifting films for highly efficient photovoltaics

Quantum dots (QDs) have been regarded as promising spectral converters for photovoltaic (PV) devices owing to their excellent photoluminescence (PL) characteristics. Herein, we report a highly-efficient QD hierarchical (QD-Hie) film that elevates the PV performance by integrating QDs with micro/nano hierarchical structures. The proposed film was designed to ensure low reflectance for incident light (air-to-device) and high reflectance for escape light (device-to-air), obtaining a light-trapping effect to increase the absorption of PVs at wide incident angles. The trapped ultraviolet photons in our film promoted the downshifting property of the QDs and amplified the generation of visible photons, thereby enhancing the PL characteristics of QDs up to 3.71 times with independency of the incidence angle. Furthermore, the hierarchical structure restricts the outward release of converted QDPL, ensuring high availability of the down-shifted photons to PVs. The optical benefit of our film was maximized by attaching them on both sides of bifacial semi-transparent dye-sensitized solar cells, resulting in the short-circuit current density (J_SC) improvement of up to 25.97% under AM 1.5G illumination. Along with its high versatility and outstanding J_SC increments, our study presents a new perspective of advanced spectral converting layers and provides practical viability for various optoelectronic devices.