Effects of Active Layer Thickness on the Performance of Polycrystalline P-β-Fesi2(Al)/Si Heterojunction Solar Cells

Active layer thickness dependence of photovoltaic (PV) properties of heterojunction solar cells fabricated using Al-alloyed polycrystalline p-type β-iron disilicide [p-β-FeSi₂(Al)]/n-Si(100) is reported. Rapid thermal annealing (RTA) at 650°C was used for the formation of polycrystalline β phase of FeSi₂ which was confirmed by x-ray diffraction (XRD). Prior to deposition of active β-FeSi₂(Al) layer, a thin Al interlayer (~8 nm) was deposited, which got dissolved in underlying Si layer during RTA and formed a heavy Al-doped epitaxial-Si (p+-Si) interfacial layer. Indium-tin-oxide (ITO) was used as top electrode. The current density-voltage and photo response characteristics of the solar cells with different active layer thicknesses (~ 50 to 135 nm) measured at room temperature are reported. Under air mass (AM) 1.5 illumination, the maximum conversion efficiency was found to be 2.18% with a short circuit current density of ~18.28 mA/cm² and open-circuit voltage of ~425 mV. The solar cells showed a series resistance of 213.6 Ω and a shunt resistance of 481.5 Ω which resulted in a fill factor of 28.05%.