“Because of the the strong performance we can achieve with low-cost, solution-processable materials, these quantum-dot-based double-pane windows and even more complex luminescent solar concentrators offer a new way to bring down the cost of solar electricity,” said researcher Victor Klimov. “The approach complements existing photovoltaic technology by adding high-efficiency sunlight collectors to existing solar panels or integrating them as semitransparent windows into a building’s architecture.”
The key is solar-spectrum splitting, which allows one pane to process separately higher- and lower-energy photons. The higher-energy photons can generate a higher voltage, which could boost the overall power output. This approach also improves the photocurrent as the dots used in the front layer are virtually reabsorption free.
The team at the Los Alamos National Laboratory used quantum dots ions of manganese that serve as highly emissive impurities. Light absorbed by the quantum dots activates these impurities. Following activation, the manganese ions emit light at energies below the quantum-dot absorption onset, eliminating the losses from self-absorption by the quantum dots.
A layer of highly emissive manganese-doped quantum dots is placed on the surface of the front glass pane and a layer of copper indium selenide quantum dots onto the surface of the back pane. The front layer absorbs the blue and ultraviolet portions of the solar spectrum, while the rest of the spectrum is picked up by the bottom layer.
Following absorption, the dot re-emits a photon at a longer wavelength, and then the re-emitted light is guided by total internal reflection to the glass edges of the window. Solar cells integrated into the window frame then collect the light and convert it to electricity. A large-area (>230 cm2) tandem window showed a high optical quantum efficiency of 6.4% for sunlight illumination and solar-to-electrical power conversion efficiency of 3.1%. The efficiency gains due to the tandem architecture over single-layer devices quickly increase with increasing size and double in structures with window sizes of more than 2,500 cm2.