Enhancement in electrical performance of thin-film silicon solar cells based on a micro- and nano-textured zinc oxide electrodes

摘要

Boron-doped ZnO (BZO) films deposited by metal organic chemical vapor deposition (MOCVD) generally act as transparent conductive oxide films in hydrogenated amorphous silicon (a-Si:H) solar cells and exhibit a high external quantum efficiency (EQE) performance in the short-wavelength region. They, therefore, facilitate efficient use of sunlight in solar cells. However, sharp surface features on the BZO film may result in nano-cracks and voids in the cells. In this study, we devised a process for modifying these sharp features. The BZO films were smoothened by performing a sputtering hydrogen-doped ZnO (HZO) layer using a magnetron sputtering system. The a-Si:H solar cells based on BZO films subjected to this treatment exhibited a higher open-circuit voltage (V_(oc)), fill factor (FF), and efficiency; however, their short-circuit current density (J_(sc)) decreased slightly. In an attempt to increase the J_(sc) while maintaining a high electrical performance for the solar cells, we deposited an additional thin BZO film on the sputter-treated one to realize a micro- and nano-textured structure. This strategy succeeded in increasing J_(sc) and also caused a further improvement in the V_(oc), FF, and efficiency. As a result, over 10% efficiency of a-Si:H solar cells based on BZO electrodes with a micro- and nano-textured structure was achieved. Moreover, the thickness of the cell is only 300 nm.