ZnO nanoparticles applied as down-shifters for solar cells
Résumé
Nowadays about 90 % of fabricated solar arrays are made of crystalline silicon (Si). There has been much research effort put into making the Si PV devices even more efficient. However, there exists a mismatch between the spectral response (SR) of a Si PV device and the solar emission spectrum due to the limited absorption of Si constituting the PV solar cell (SC) active layer. In out researche, the optical properties of ZnO nanoparticles (NPs) fabricated by three different methods were studied by UV-excited continuous wave photoluminescence in order to estimate their down-shifting efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device, thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiodes with a low UV sensitivity (about 8 %), ZnO luminescent layer produces a down-shifting effect and the EQE of the UV and blue range improves by 16.6 %, while for the photodiodes with higher UV sensitivity (about 50 %), the EQE in this range decreases with the ZnO layer thickness due to other competing effects like the diminution of the ZnO layer transmittance and an increasing diffusion.