Indium tin oxide obtained by high pressure sputtering for emerging selective contacts in photovoltaic cells.

Abstract

This article studies the physical and electrical behavior of indium tin oxide layers (ITO) grown by an unconventional

technique: High Pressure Sputtering (HPS), from a ceramic ITO target in a pure Ar atmosphere. This

technique has the potential to reduce plasma induced damage to the samples. The aim is to obtain, at low

temperature via HPS, good quality transparent conductive oxide layers for experimental photovoltaic cells with

emerging selective contacts such as transition metal oxides, alkaline metal fluorides, etc. We found that the

resistivity of the films was strongly dependent on Ar pressure. To obtain device-quality resistivity without

intentional heating during deposition a pressure higher than 1.0 mbar was needed. These films deposited on glass

were amorphous, presented a high electron mobility (up to 45 cm2V􀀀 1s􀀀 1) and a high carrier density (2.9 × 1020

cm􀀀 3 for the sample with the highest mobility). The optimum Ar pressure range was found at 1.5–2.3 mbar.

However, the resistivity degraded with a moderate annealing temperature in air. Finally, the feasibility of the

integration with photovoltaic cells was assessed by depositing on Si substrates passivated by a-Si:H. The film

deposited at 1.5 mbar was uniform and amorphous, and the carrier lifetime obtained was 1.22 ms with an

implied open circuit voltage of 719 mV after a 215 ◦C air anneal. The antireflective properties of HPS ITO were

also demonstrated. These results show that ITO deposited by HPS is adequate for the research of solar cells with

emerging selective contacts.