Improving the photocurrent of a-Si:H/CIGS hybrid tandem cells by texturing ZnO:Al

To reduce the usage of Indium (rare material) in CIGS, ultra thin, high efficiency CIGS based solar devices have been developed in our group. One approach is to fabricate hybrid tandem cells between hydrogenated amorphous silicon and CIGS. Because the a-Si:H top sub-cell limits the current of such a device, it is desirable to texture the top transparent conductive oxide of the tandem cells for better light in-coupling inside the active layers. This project focused on textured ZnO:Al as the top TCO for the hybrid tandem cells to improve the device’s current. In this project, substrate temperature and sputtering pressure were varied. By varying sputtering conditions, different texture types of ZnO:Al could be found by wet-etching in HCl 0.5%. The different morphologies of textured ZnO:Al could be explained by the compactness of the material. The textured ZnO:Al had high transparency (around 80%) and low resistivity (as low as 5.5e-4 Ohm.¬cm). Then, further examination on the effect of light trapping of different textured ZnO:Al, textured a-Si:H single junctions were made. It was found that the textured top TCO resulted in maximum 9% increase in short circuit current in wavelength range from 300nm to 600nm of the textured single junction cell. This assisted the textured ZnO:Al choices for hybrid tandem cell. In textured hybrid tandem cells, the current of the top sub-cells increased by 0.77mA/cm2 or 8% increment in device’s current. Aside the experimental work on the textured devices, a new empirical model "AID model" was developed to integrate in the GenPro4 model. This empirical model took advantage of spectrophotometer measurements to generate the vectors inside the scattering matrices to describe light’s behaviour at the interface. Incorporating the AID model with other models, GenPro4 can be used with a wider spectrum of textured surfaces.Electrical Engineering, Mathematics and Computer ScienceElectrical Sustainable EnergySustainable Energy Technolog