Analysis of a Bismuth Sulfide/Silicon Junction for Building Thin Film Solar Cells

Feasibility of combining p-type crystalline Si (c-Si) of 200–8000 nm in thickness with an n-type bismuth sulfide (Bi 2 S 3 ) thin film of 300 nm in thickness for thin film solar cell is analyzed. Theoretical analysis shows that the high optical absorption coefficient (10 5 cm −1 ) of Bi 2 S 3 results in a light-generated current density ( J L ) of >20 mA/cm 2 for a c-Si(200 nm)/Bi 2 S 3 (300 nm) stack at a combined film thickness of 500 nm, and with an open circuit voltage ( V oc ) of nearly 600 mV. Proof-of-concept cell structures were prepared on p-type c-Si wafers of electrical resistivity 1 Ω cm. Any oxide layer at the interface significantly deteriorates the cell parameters. In a cell prepared using evaporated n-Bi 2 S 3 on (p) c-Si, J sc is 3 mA/cm 2 ; V oc is 360 mV; and η is 0.5%; which improved to: 7.2 mA/cm 2 , 485 mV and 1.7%, respectively, after heating the cell in forming gas. A cell with an Sb 2 S 3 (40 nm) thin film as an antireflective coating on Bi 2 S 3 , produced: J sc of 10 mA/cm 2 ; V oc of 480 mV; and η of 2.4%. Theoretical simulation suggests that better cell fabrication could lead to: J sc of 26 mA/cm 2 ; V oc of 600 mV; and η of 10%.