Efficiency improvement of commercial silicon solar cells using bilayers of luminescent nanomaterials

Photoluminescent down-shifting Silicon (Si) and Zinc Oxide (ZnO) Quantum Dots (QDs) were synthesized and employed in spectral converter layers to increase the photovoltaic performance of commercial solar cells. Poly-methyl-methacrylate (PMMA) was used as a matrix host to provide a transparent support for the quantum dots. The thickness of the photoluminescent QD layers and the particle concentration in the polymer were optimized to reduce reflectivity and increase the power generation. Different luminescent films’ configurations were tested on fully functional solar cells, including single type of QD (Si or ZnO) layer and double layer of QDs (Si + ZnO). The colloidal QDs presented optical bandgaps of 2.97 eV and 3.40 eV for the Si QDS and ZnO QDs, respectively, difference that was advantageous for a double-layer configuration. The absorption of both Si QDS and ZnO QDs was mainly in the UV region, while their luminescence consisted of broad bands centered at 525 nm and 545 nm, respectively, providing an attractive stokes shift to be employed as spectral converter layer. The combination of UV absorption, downshifted emission, and reflectivity reduction by the QD-based layers produced improvements in the power conversion efficiencies of commercial silicon solar cells from 14.42 to 15.36%, which represent an overall improvement of ~ 6.5%. The collected results represent a promising strategy to improve the photovoltaic performance of new and existing devices.