Influence of Selenium Pressure on Properties of AgInGaSe2 Thin Films and Their Application to Solar Cells

TL;DR

This paper studies how selenium pressure affects the properties of AgInGaSe2 thin films and their performance in solar cells.

Contribution

The study reveals a two-stage mechanism and optimal selenium pressure for enhancing solar cell performance.

Findings

Higher selenium pressure increases grain size and surface roughness of AIGS films.

AIGS solar cells achieved 9.6% efficiency at 2.1 × 10−3 Torr selenium pressure.

Low selenium pressure leads to higher bandgap due to anti-site defects.

Abstract

A wide-bandgap AgInGaSe2 (AIGS) thin film was fabricated using molecular beam epitaxy (MBE) via a three-stage method. The influence of Selenium (Se) pressure on the properties of AIGS films and solar cells was studied in detail. It was found that Se pressure played a very important role during the fabrication process, whereby Se pressure was varied from 0.8 × 10−3 Torr to 2.5 × 10−3 Torr in order to specify the effect of Se pressure. A two-stage mechanism during the production of AIGS solar cells was concluded according to the experimental results. With an increase in Se pressure, the grain size significantly increased due to the supply of the Ag–Se phase; the superficial roughness also increased. When Se pressure was increased to 2.1 × 10−3 Torr, the morphology of AIGS changed abruptly and clear grain boundaries were observed with a typical grain size of over 1.5 μm. AIGS films fabricated with a low Se pressure tended to show a higher bandgap due to the formation of anti-site defects such as In and Ga on Ag sites as a result of the insufficient Ag–Se phase. With an increase in Se pressure, the crystallinity of the AIGS film changed from the (220)-orientation to the (112)-orientation. When Se pressure was 2.1 × 10−3 Torr, the AIGS solar cell demonstrated its best performance of about 9.6% (Voc: 810.2 mV; Jsc: 16.7 mA/cm2; FF: 71.1%) with an area of 0.2 cm2.

Figures