Bandgap Engineering and Impedance Spectroscopy Analysis of Linearly Graded Group IV Material-based Alloys for Photovoltaic Applications
摘要
We report a comprehensive numerical study of single-junction photovoltaic devices incorporating linearly graded Si1-x-yGeySnx absorber layers, performed using the SCAPS-1D simulator. Four compositional profiles—Si0.75-xGe0.25Snx, Si0.70-xGe0.30Snx, Si0.65-xGe0.35Snₓ, and Si0.60Ge0.40Snx—were engineered over a 1 μm thickness to achieve graded bandgaps from 1.28 eV down to 1.19 eV, extending the absorption edge from 970 nm to 1,040 nm. Optimization of absorber thickness, doping densities (1012–1018 cm−3 acceptors), trap densities (1010–1015 cm−3), and capture cross Sects. (10–20–10–10 cm2) yielded peak power conversion efficiencies of 26.02%, 26.37%, 26.25%, and 25.77%, respectively. Corresponding short-circuit current densities (27.95–30.60 mA/cm2) and open-circuit voltages (1.00–1.08 V) highlight the trade-off between photocurrent enhancement and voltage retention. External quantum efficiency profiles exhibited gradual roll-off beyond the critical wavelength, with peak spectral responses of 0.510 A/W (750 nm), 0.542 A/W (800 nm), 0.539 A/W (790 nm), and 0.519 A/W (770 nm). Impedance spectroscopy (10–12–1012 Hz) demonstrated reduced charge-transfer resistance with thicker absorbers and a resistive-to-capacitive transition between 10–2 and 102 Hz, beyond which capacitive bypassing dominates. Johnson-Nyquist noise analysis revealed series noise attenuation at low frequencies and parallel noise emergence at high frequencies, elucidating charge-transport regimes. These findings establish a robust theoretical framework for SiGeSn ternary alloys, providing critical design guidelines for bandgap engineering, interface optimization, and noise management in next-generation high-efficiency photovoltaic technologies.