Microcrystalline silicon solar cells deposited at high rates

Abstract

Hydrogenated microcrystalline silicon (μc-Si:H) thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under high working pressure. The influence of deposition parameters on the deposition rate (RD) and the solar cell performance were comprehensively studied in this paper, as well as the structural, optical, and electrical properties of the resulting solar cells. Reactor-geometry adjustment was done to achieve a stable and homogeneous discharge under high pressure. Optimum solar cells are always found close to the transition from microcrystalline to amorphous growth, with a crystallinity of about 60%. At constant silane concentration, an increase in the discharge power did hardly increase the deposition rate, but did increase the crystallinity of the solar cells. This results in a shift of the μc-Si:H∕a-Si:H transition to higher silane concentration, and therefore leads to a higher RD for the optimum cells. On the other hand, an increase in the total flow rate at constant silane concentration did lead to a higher RD, but lower crystallinity. With this shift of the μc-Si:H∕a-Si:H transition at higher flow rates, the RD for the optimum cells decreased. A remarkable structure development along the growth axis was found in the solar cells deposited at high rates by a “depth profile” method, but this does not cause a deterioration of the solar cell performance apart from a poorer blue-light response. As a result, a μc-Si:H single-junction p-i-n solar cell with a high efficiency of 9.8% was deposited at a RD of 1.1 nm∕s.