Incorporation and critical concentration of oxygen in a-Si:H solar cells

• Published in: Solar energy materials and solar cells Vol. 95; no. 10; pp. 2811 - 2815
• Main Authors: Woerdenweber, J., Merdzhanova, T., Gordijn, A., Stiebig, H., Beyer, W.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2011; Elsevier
• Subjects: a-Si:H; Applied sciences; Base pressure; Chemical vapor deposition; Contamination; Decay; Deposition; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; Hydrogen storage; Light-soaking; Natural energy; Oxygen; PECVD; Photoelectric conversion; Photovoltaic cells; Photovoltaic conversion; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Walls; Solar cells; Oxygen; PECVD; Light-soaking; Contamination; a-Si:H; Performance evaluation; Gas mixture; Hydrogen; Deposition process; Gas flow; Illumination; Silicon solar cells; Absorbent material; Initial condition; Deposition rate; Chemical vapor deposition; Operating conditions; High pressure; Solar cell; Process conditions; Manufacturing process; Amorphous hydrogenated material; High efficiency; Oxygen pressure; Comparative study
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2011.05.035

For different process conditions, series of hydrogenated amorphous silicon p-i-n solar cells with various oxygen concentrations in the intrinsic absorber layer were fabricated by plasma-enhanced chemical vapor deposition at 13.56 MHz using process gas mixtures of SiH 4 and H 2. Oxygen was introduced into the gas phase during the deposition process by a controllable leak in the chamber wall and the amount of oxygen supply is characterized by the oxygen base pressure p b . It is found that for a certain deposition regime defined by silane and H 2 flows, deposition pressure and substrate temperature the oxygen incorporation follows an expected dependence on the ratio p b / r d with r d the deposition rate. This relation is not valid for the comparison of different deposition regimes. A high hydrogen flow is found to reduce the oxygen incorporation strongly. The photovoltaic parameters of the solar cells were measured in the initial state as well as after 1000 h of light-soaking. The critical oxygen concentration (i.e. the upper limit of incorporated oxygen not leading to a decay of the solar cell performance) was determined for each regime in the initial and light-soaked state. For all deposition regimes, the results show no difference in these critical oxygen concentrations for the initial and light-soaked state. The critical oxygen concentration, is found to differ for the different process regimes and turns out to be the highest (approximately 1×10 20 cm −3) for the deposition regime with the highest hydrogen flow rate, which interestingly is the regime with the lowest oxygen incorporation at a given p b / r d ratio. This combination makes the regime of high hydrogen gas flow suitable for depositing high-efficiency solar cells at high base pressure. [Display omitted] . ► The critical oxygen concentration is unaffected by light-induced-degradation. ► High process gas flows lead to high critical oxygen concentrations. ► High process gas flows lead to a low incorporation ratio.