Back Contact Optimization for Sb<sub>2</sub>Se<sub>3</sub> Solar Cells

Abstract

Antimony selenide (Sb<sub>2</sub>Se<sub>3</sub>) has advantages of low-toxicity, abundant and excellent photoelectric properties. It is widely considered as one of the most promising light-harvesting materials for thin-film solar cells. However, the power conversion efficiency of the Sb<sub>2</sub>Se<sub>3</sub> thin-film solar cell is still far inferior to that of cadmium telluride, copper indium gallium selenium and perovskite solar cells. As known, the Sb<sub>2</sub>Se<sub>3</sub> solar cell performance is closely related to the light absorber layer (crystallinity, composition and bulk defect density, etc.), PN heterojunction quality (charge carrier concertation, energy band alignment and interface defect density, etc.) and back-contact barrier formation, which determines the process of carrier generation, excitation, relaxation, transfer and recombination. The low fill factor is one of the core problems that limit further efficiency improvement of Sb<sub>2</sub>Se<sub>3</sub> solar cells, which can be attributed to the high potential barrier at the back contact between the Mo electrode and Sb<sub>2</sub>Se<sub>3</sub>absorption layer. In this work, a heat treatment is applied to the Mo electrode to generate a MoO<sub>2</sub>buffer layer. It can be found that this buffer layer can inhibit MoSe<sub>2</sub> film growth, exhibiting better ohmic contact with Sb<sub>2</sub>Se<sub>3</sub> and reducing the back contact barrier of the solar cell. Sb<sub>2</sub>Se<sub>3</sub> thin film is prepared by an effective combination reaction involving sputtered and selenized Sb precursor. After introducing the MoO<sub>2</sub>buffer layer, it can also promote the formation of (hk1) (including (211), (221) and (002) etc.) preferentially oriented Sb<sub>2</sub>Se<sub>3</sub> thin films with average grain size over 1 μm. And the ratio of Sb and Se was optimized from 0.57 to 0.62, approaching the stoichiometric ratio of Sb<sub>2</sub>Se<sub>3</sub> thin film and inhibiting the formation of <em>V<sub>se</sub> </em>and <em>Sb<sub>Se</sub></em> defects. Finally, it enhances the open-circuit voltage (<em>V<sub>OC</sub></em>) of solar cells from 0.473 V to 0.502 V, short-circuit current density (<em>J<sub>SC</sub></em>) from 22.71 mA/cm<sup>2</sup> to 24.98 mA/cm<sup>2</sup>, and fill factor (<em>FF</em>) from 46.90% to 56.18%, establishing a promotion in power conversion efficiency (<em>PCE</em>) from 5.04% to 7.05%. This work proposes a facile strategy for interfacial treatment and elucidates the related carrier transport enhancement mechanism, paving a bright avenue to overcome the efficiency bottleneck of Sb<sub>2</sub>Se<sub>3</sub> thin film solar cells.