Investigation of current mechanisms in a-Si:H alloy solar cells

The characteristics of a-Si:H solar cells depend on their past histories, namely, voltage and light soaking times and thermal annealing. The effect of light soaking is known to reduce cell efficiencies at the ten percent level. The details of the role of cell history on the basic current mechanisms are not well understood. The objective of this work is to identify the current mechanisms in I-V characteristics and elucidate their roles in cell stability. Commercial-grade single-junction solar cells with 0.35 cm² active areas and 200, 500 and 800 nm thick intrinsic layers were the focus of the investigations. The cells were characterized with light and dark I-V measurements. The effects of temperature and annealing cycles were investigated. A parametric fitting model was used to quantify four current mechanisms under forward-bias conditions, namely, shunt and series resistances, current injection and depletion. The current mechanisms under reverse-bias conditions are not understood but have been characterized. The investigations show the greatest instability under forward-bias conditions occurs in the shunt resistance mechanism