Impact of hydrogen dilution on microstructure and optoelectronic properties of silicon films deposited using trisilane

Abstract

We explored the deposition of hydrogenated amorphous silicon (a-Si : H) using trisilane (Si3H8) as a gas precursor in a radiofrequency plasma enhanced chemical vapour deposition process and studied the suitability of this material for photovoltaic applications. The impact of hydrogen dilution on the deposition rate and microstructure of the films is systematically examined. Materials deposited using trisilane are compared with that using disilane (Si2H6). It is found that when using Si3H8 as the gas precursor the deposition rate increases by a factor of ∼1.5 for the same hydrogen dilution (R = [H2]/[Si3H8] or [H2]/[ Si2H6]). Moreover, the structural transition from amorphous to nanocrystalline occurs at a higher hydrogen dilution level for Si3H8 and the transition is more gradual as compared with Si2H6 deposited films. Single-junction n-i-p a-Si : H solar cells were prepared with intrinsic layers deposited using Si3H8 or Si2H6. The dependence of open circuit voltage (Voc) on hydrogen dilution was investigated. Voc greater than 1 V can be obtained when the i-layers are deposited at a hydrogen dilution of 180 and 100 using Si3H8 and Si2H6, respectively.