The structural, optical, and electrical properties of thermal evaporation-deposited V2OX films for use in silicon heterojunction solar cells

Vanadium suboxide (V₂O_x) has been suggested as a promising transition metal oxide for the development of selective contacts on high-performance crystalline silicon heterojunction solar cells. In this study, V₂O_x thin films were deposited on wet-cleaned wafers (Cz n-type c-Si (111) with a thickness of 160 μm; cleaning steps include SAW damage removal, RCA1, RCA2, and HF dip) and Corning (Eagle 2000) glass substrates utilizing the thermal evaporation technique at a pressure of 5 × 10⁻⁵ mbar. V₂O_x thin films were deposited with various thicknesses from 5 to 20 nm. Ellipsometry, XRD, AFM, UV–Vis analysis, minority carrier lifetime measurements using SINTON photoconductivity decay (PCD) and lifetime mapping by SEMILAB µ-PCD were used to figure out the structural, optical, and electrical properties of deposited V₂O_x films. The thickness of these films was measured by the ellipsometry technique. The amorphous nature of the as-deposited films is confirmed by the XRD patterns, and their optical transmittance is in the range of 93 to 76% in the visible range for 5 to 20 nm for V₂O_x films. At 1 sun illumination, the minority carrier lifetime values range from 220.40 ± 1.26 µs to 293.27 ± 0.63 µs. These values are within the range of well-passivated wafers, they translate into implied-V_OC values ranging from 642 to 652 mV, indicating a high degree of surface passivation. Surface passivation could be caused by a sub-stoichiometric SiO_x interlayer that forms when silicon bonds with oxygen. We postulate that the fixed charges acquired by the silicon sub-oxide layers create the field effect passivation. According to our experimental findings, a 10 nm-thick V₂O_x film has the best optoelectronic properties, including a minority life-time of 293.27 ± 0.63 µs with an implied V_oc of 652 mV. The findings are critical for the fabrication of hetero-junction silicon solar cells.