Down-shifting and antireflective effects of ZnO/PMMA thin films and their influence on silicon solar cells performance

The down-shifting effect of nanostructured II-VI semiconductors like zinc oxide (ZnO) is an attractive feature that can be exploited for the performance enhancement of silicon solar cells. The UV-region of the solar spectrum can be harvested more efficiently by the silicon solar cell after being absorbed by ZnO quantum dots (QDs) and re-emitted in the visible range (centered ⁓510 nm). Additionally, the polymeric matrix (PMMA) used for the fabrication of the ZnO/PMMA thin films can serve as an antireflective layer, enabling a better overall solar radiation absorption. The present study discusses the synthesis and characterization of photoluminescent ZnO QDs and their effect on the performance of in-house-fabricated single crystal silicon solar cells. The down-shifting effect of the colloidal quantum dots was characterized by collecting and analyzing their absorption and photoluminescence spectra. The structural characterization of the obtained ZnO QDs was performed employing X-ray diffraction (XRD) and transmission electronic microscopy (TEM). Before the deployment of the ZnO QDs thin film layers, the optimal thickness of the PMMA matrix was evaluated by ellipsometry seeking the optimal antireflective effect. The performance characteristics of the solar cells before and after the application of the ZnO/PMMA layers were determined from the J-V curves generated in a solar simulator and their spectral response was evaluated by external quantum efficiency (EQE) measurements achieving a maximum relative PCE increase above 19%.