Interfacial assessment of degraded amorphous silicon module using scanning probe microscopy

Abstract

This is a study of the degradation of amorphous silicon solar cells. The study accessed structural defects and the mechanical stress of solar cells at nanoscale level. Interface morphology, deformation, and internal delamination of the cells were analyzed. Adequate analysis of roughness parameters was performed to investigate the state of degradation of the amorphous silicon solar modules (a-Si:H) used in this study. Roughness parametric test is necessary in thin film solar cells production process because it is used to quantify the relationship that exists between roughness parameters and electrical efficiencies of solar cells. However, in this study, a roughness analysis was not only performed to quantify the performance of the a-Si:H module but to also compliment their mechanical degradation analysis. Roughness indicators such as root means square (RMS) roughness and average roughness were acquired from line profiles. Measurements were taken with scanning probe microscope (SPM) and PeakForce Quantitative Nanomechanical (QNM) technique was used through the cross sectional area of the analyzed samples. The method was validated with adhesive force and deformation analyses; it was established that high roughness values result from mechanical degradation. Results from the roughness parameters and the mechanical degradation analysis were further observed from in situ measurements and these showed good compatibility. The benefit of this technique is that it provides a good procedure for the evaluation of mechanical degradation without destroying any part of the intrinsic layers in a-Si:H modules.