Microcrystalline Si:H solar cells fabricated using ECR plasma deposition

Abstract

The properties of microcrystalline Si:H materials and solar cells fabricated using remote, low pressure ECR (electron cyclotron resonance) plasma deposition are described. p+nn+ junction solar cells were deposited at 275–325°C on stainless steel substrates using mixtures of silane and hydrogen. Microcrystalline layers and solar cells could be produced even for low dilution ratio of hydrogen/silane of 8:1. It was found that once crystallisation started, one could decrease the hydrogen/silane ratio and still obtain microcrystalline Si:H solar cells. The voltage of the solar cells could be improved by tailoring the interface between p+ and n layers. An amorphous interfacial layer improved the voltage. A thin amorphous Si:H layer at the back, between n+ and n layers was used to significantly reduce the shunt resistance. Standard device analyses, including dark I(V) curves and capacitance measured at several frequencies, revealed that device characteristics could be understood in terms of a standard Si diode model. The doping densities in the n layer were found to be in the 1×1015 to 2×1016/cm3 range and could be adjusted by altering the amount of compensatory B doping of the layer. The influence of the addition of He dilution to the mixture was also studied, and it was found that He degraded the crystallinity, though it increased the growth rate and open-circuit voltage.