3, Applied Math, University of California, Merced, Merced, California, United States
2, Materials Science and Engineering, University of California Merced, Merced, California, United States
The recent re-emergence of luminescent solar concentrators (LSCs) as viable devices for solar energy harvesting can be attributed to the impressive progress in materials development and engineering. The resultant products have demonstrated effective broadband absorption, high external quantum yield (QY) and spectral properties that allow for almost negligible self-absorption (SA) losses. Our research has focused on investigating the ramifications of different active materials and device architectures on LSC performance, including efficiency and photostability. I will begin with a discussion of our work regarding the use of near infra-red lead sulphide (PbS) quantum dots (QDs) as in planar LSCs. The results of this study indicated that PbS LSCs generate nearly twice the photocurrent in silicon cells compared to a traditional dye and cadmium selenide QDs, achieving an integrated optical efficiency ηopt of 12.6%. This was primarily due to the broadband absorption of PbS, and a smaller overlap between the absorption and emission spectra, which reduces SA. However, despite the superior performance, PbS also exhibits a gradual and permanent photo-oxidation, which decreases the photocurrent at the rate of 0.1% per minute. Tuning the device architecture led to some improvements in PbS-based LSCs, as we demonstrated next, fabricating solid and hollow cylinders from a composite of QDs in polymethylmethacrylate. The experimental results were in good agreement with theoretical calculations, with hollow LSCs having a higher absorption of incident radiation and lower SA compared to solid cylindrical and planar geometries with similar geometric factors. In addition to optical efficiency almost thrice that of planar LSCs, these also exhibited improved photo-stability under both laboratory and external ambient conditions. Most recently, we have begun exploring the suitability of organic–inorganic hybrid perovskite (PVSK) thin films as the active medium in planar LSCs. PVSK compounds are at the forefront of photovoltaic research, and their high refractive index, broad absorption spectrum, and superior QY make them theoretically ideal candidates for LSCs. In practice, however, the possibility of high self-absorption in a continuous film, coupled with the inherent instability of PVSK materials, have hindered their use. Our results display an impressive ηopt in the range 15%–29% despite high SA losses, and the devices remain operational for up to seven weeks in ambient conditions. We attribute this to the high QY and refractive pushed the efficiency to 34.7%. Further, using 3D Monte Carlo simulations that incorporate our experimental results, we have demonstrated the possibility of scaling these LSCs up to almost 100 cm, thereby providing a route toward optimizing thin film PVSK materials for these and other optoelectronic and photovoltaic applications.
This work was supported by funds from the National Aeronautics and Space Administration grant no. NNX15AQ01A.