External quantum efficiency analysis of Si solar cells with II-VI nanocrystal luminescent down-shifting layers

Luminescent down-shifting (LDS) as a purely optical approach increases a solar cell's ultra-violet to blue response by shifting short-wavelength light to longer-wavelengths where the external quantum efficiency (EQE) of solar cells is higher. We propose a simple, universally applicable, optical model to analyze EQE spectra of solar modules with LDS layers using only two parameters. The model is successfully tested on ethylene-vinyl acetate encapsulated Si solar cells with CdSe/ZnS nanocrystals as luminescent particles. For a beneficial effect in the investigated system, LDS efficiencies (the fraction of photons transmitted into the cell compared to photons absorbed by the LDS layer) of more than 0.8 are needed with a maximum possible short-circuit current increase of + 3.4%.