Electronic, optical, and kinetic properties of silicon alloys and their application in renewable energy sources

Abstract

The results of studies on the physical properties of hydrogenated amorphous thin films of the alloys a-Si_1-xGe_x:H, a-Si:H, and a-Ge:H, obtained by plasma-enhanced chemical vapor deposition, are presented. The optical constants ($n$, $n_1$, $\alpha$, $R$,T, $d$) and the band gap of the studied films ($E_0=1.05÷1.85$ eV) have been determined.Based on the investigation of the optical properties under various deposition conditions—including film thickness ($d$, $H_2$), hydrogen partial pressure ($H_2$), substrate temperature, and hydrogenation level of the alloys—the films were found to exhibit different structural phases. By varying the technological parameters, different structural phases of crystallites can also be obtained. The structure of the deposited a-Si_(1-x) Ge_x:H, а-Si:H, а-Ge:H is mixed (two-phase) and consists of nanocrystallites of nc $-\text{Si}:H$ “distributed” within an amorphous matrix. The concentration of carbon and hydrogen in the $a-{\text{Si}}_{1-x}{\text{Ce}}_x:H$ films depends on the deposition conditions and the initial gas mixture $S$ iH₄, H₂, GeH₄. It was established that the film properties strongly depend on the composition and hydrogenation level. The amount of hydrogen atoms in the films was varied by adjusting the gas mixture composition and measured via infrared (IR) absorption spectroscopy for а-Si:H and а-Ge:H. films. The paper investigates the changes in the electrical and photoelectric characteristics and the effect of radiation on their properties. Solar cells based on а-Si:H and а-Si_0,88Ge_0,12:H films were fabricated in two-layer, three-layer, and two-plus-three-layer cascade structures; their performance characteristics were measured. It was found that for a cell area of 1,5 cm², the maximum power conversion efficiency (η) reaches 18,9 %.