Abstract
This paper describes the synthesis and characterization of Si and CdTe quantum dots (QDs) and their use, either on their own or combined, as photoluminescent (PL) down-shifting nanostructured coatings aimed to enhance the photovoltaic efficiency of polycrystalline silicon solar cells. To this end, the front face of a set of silicon cells was coated with different volume ratios of the above-mentioned QDs, or some of its mixtures, dispersed in PMMA layers. Previously, the absorption and the PL (exc = 380 nm) response of the dispersions of the QDs were measured. It was observed that the PL response of the mixtures was strongly affected in location, spread, and intensity of the emission peak according to the volume ratio involved. As compared to the unmixed CdTe samples, a notorious red-shift of the main peak location was obtained for a couple of mixed QDs’ dispersions, which was one of the project objectives given that Si solar cells respond better to photons with wavelengths in the 650–700 nm range. This effect was confirmed in a set of polycrystalline Si solar cells covered with and without nanostructured PMMA/QDs layers tested under AM 1.5G solar simulator conditions. It was found that the use of the proposed mixtures of QDs gave an increase of 1.53% in solar cell power conversion efficiency.
Highlights
The total solar energy density outside the atmosphere, known as the irradiance solar constant at AM0 conditions, is ISC = 1367 Watt/m2; and approximately, 98% of the power density in the solar spectrum lays in the 200–2500 nm wavelength range, that is, from the near UV to the medium near IR and has a modal peak at about 500 nm
Si solar cells are affected by other losses mainly related to carrier low lifetime and/or short diffusion length which imply increased e–h pair recombination loss rate [2]. This loss is monitored in solar cells by measuring their external quantum efficiency (EQE), which provides the spectral information regarding how close a single absorbed photon is of producing an effective circuit current of one electron
Note that an allowed direct interband optical transition type was detected for the Si quantum dots (QDs) case in contrast to the well-established indirect nature for the bulk material
Summary
It has been reported that, due to fundamental losses, the maximum efficiency theoretically achievable in a Si solar cell is of 30.1%
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