RESUMEN
The term 'Solar Cell' is commonly used for Photovoltaics that convert light into electrical energy. However, light can be harvested from various sources not limited to the Sun. This work considers the possibility of harvesting photons from different star types, including our closest neighbor star Proxima Centauri. The theoretical efficiency limits of single junction photovoltaic devices are calculated for different star types at a normalized light intensity corresponding to the AM0 spectrum intensity with AM0 = 1361 W/m2. An optimal bandgap of > 12 eV for the hottest O5V star type leads to 47% Shockley-Queisser photoconversion efficiency (SQ PCE), whereas a narrower optimal bandgap of 0.7 eV leads to 23% SQ PCE for the coldest red dwarf M0, M5.5Ve, and M8V type stars. Organic Photovoltaics (OPVs) are the most lightweight solar technology and have the potential to be employed in weight-restricted space applications, including foreseeable interstellar missions. With that in mind, the Sun's G2V spectrum and Proxima Centauri's M5.5Ve spectrum are considered in further detail in combination with two extreme bandgap OPV systems: one narrow bandgap system (PM2:COTIC-4F, Eg = 1.14 eV) and one wide bandgap system (PM6:o-IDTBR, Eg = 1.62 eV). Semi-empirically modeled JV-curves reveal that the absorption characteristics of the PM2:COTIC-4F blend match well with both the G2V and the M5.5Ve spectrum, yielding theoretical PCEs of 22.6% and 12.6%, respectively. In contrast, the PM6:o-IDTBR device shows a theoretical PCE of 18.2% under G2V illumination that drops sharply to 0.9% under M5.5Ve illumination.
RESUMEN
Cu-Sn-S (CTS) thin films were deposited onto bare and molybdenum (Mo) coated glass substrates by means of the spray pyrolysis technique under different conditions. The CTS thin films obtained are shown, by means of Raman spectroscopy, to consist of two main phases: Cu2SnS3 and Cu3SnS4 as well as of the secondary phase of Cu2-xS. The electrical conductivity of the spray-deposited p-type CTS thin films under investigation is determined by two shallow acceptor levels: Ev+0.07 eV at T<334 K and Ev+0.1 eV at T>334 K. The material of the CTS thin films was established to be a direct-band semiconductor with the bandgap Eg=1.89 eV. The SEM and x-ray energy dispersive analysis show the surface and cross section of the CTS thin film deposited onto molybdenum-coated glass ceramics substrate with the actual atomic ratios of Cu:Sn:S being 2.9:1:2.64, which is in good agreement with the Raman spectra. Also, a small content of residual Cl atoms was found in the CTS thin films under investigation as the by-product of the pyrolytic reactions.
