Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for terrestrial and space-based photovoltaics (PVs). Due to their high emission efficiencies and readily tunable emission and absorption spectra, colloidal quantum dots (QDs) have emerged as promising LSC fluorophores, superseding dye molecules previously dominating the LSC field. An important advantage of the QDs over dye-based systems is a possibility to greatly reduce losses to re-absorption by displacing the emission band from the onset of strong optical absorption, the approach commonly referred to as "Stokes-shift engineering." Spectral tunability of the QDs also facilitates the realization of stacked multi-layered LSCs wherein the enhanced performance is obtained through spectral splitting of incident sunlight, as in multi-junction PVs. This presentation will discuss several approaches to Stokes-shift engineering with II-VI [1,2] and I-III-VI2 [3,4] QDs and also describe the first example of a large-area (>200 cm2) tandem LSC based on two types of nearly reabsorption-free QDs spectrally-tuned for optimal solar-spectrum splitting . This prototype device exhibits a record-high optical quantum efficiency of more than 6% for sunlight illumination and solar-to-electrical power conversion efficiency of >3%. Due to their strong performance achievable with low-cost, solution-processible materials, QD-based LSC tandems can provide a viable pathway for further reducing the cost of solar electricity by complementing the existing PV technology with inexpensive, high-efficiency sunlight collectors deployable either as strongly absorbing LSC-PV modules or semi-transparent building-integrated solar windows.
1. Meinardi, F., Colombo, A., Velizhanin, K. A., Simonutti, R., Lorenzon, M., Beverina, L., Viswanatha, R., Klimov, V. I. & Brovelli, S. Large-area luminescent solar concentrators based on ‘Stokes-shift-engineered’ nanocrystals in a mass-polymerized PMMA matrix. Nature Phot. 8, 392-399 (2014).
2. Li, H., Wu, K., Song, H.-J. & Klimov, V. I. Doctor-blade deposition of quantum dots onto standard window glass for low-loss large-area luminescent solar concentrators. Nature Energy 1, 16157 (2016).
3. Meinardi, F., McDaniel, H., Carulli, F., Colombo, A., Velizhanin, K. A., Makarov, N. S., Simonutti, R., Klimov, V. I. & Brovelli, S. Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots. Nature Nanotech. 10, 878-885 (2015).
4. Klimov, V. I., Baker T. A., Lim J., Velizhanin, K. A., McDaniel H. Quality Factor of Luminescent Solar Concentrators and Practical Concentration Limits Attainable with Semiconductor Quantum Dots, ACS Phot. 3, 1138 -1148 (2016)
5. Wu, K., Li, H.,. & Klimov, V. I. Tandem luminescent solar concentrators based on engineered quantum dots, submitted (2017).