An analysis of thin film silicon for photovoltaic applications

Abstract

a-Si:H solar cells typically exhibit instability due to intrinsic layer degradation and hydrogen movement. An alternative way to circumvent the a-Si:H solar cell problem is to make use of heterostructure type cells (a-Si:H/poly-Si). The objective of this paper is to characterize properties of thin film amorphous and poly-Si aiming at a heterostructure type solar cell. The material characteristics of the as-grown a-Si:H films are compared with those of the anneal treated films. The structural, optical, and electrical properties were investigated. The anneal treatment changed structural properties as well as electrical and optical characteristics of the film. Resistance, capacitance, dielectric constant, refractive index, and light absorption coefficient are reduced with crystallization of the a-Si:H. Mobility, conductivity, and transmittance are increased after crystallization. The poly-Si grain boundary trap type and activation energy were determined by thermally stimulated current (TSC) measurement. Grain boundary trap type and activation energy were detected by the TSC study. Hole traps dominated after high temperature anneal with activation energy of 0.49 eV. The field effect mobility was increased from 1.6/spl times/10/sup -3/ cm/sup 2//V.s for as-grown amorphous silicon to 67 cm/sup 2//V.s for 850/spl deg/C annealed and hydrogen grain boundary passivated poly-Si.