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

Abstract

Feasibility of combining p-type crystalline Si (c-Si) of 200–8000 nm in thickness with an n-type bismuth sulfide (Bi2S3) thin film of 300 nm in thickness for thin film solar cell is analyzed. Theoretical analysis shows that the high optical absorption coefficient (105 cm−1) of Bi2S3 results in a light-generated current density (JL ) of >20 mA/cm2 for a c-Si(200 nm)/Bi2S3(300 nm) stack at a combined film thickness of 500 nm, and with an open circuit voltage (Voc ) 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-Bi2S3 on (p) c-Si, Jsc is 3 mA/cm2; Voc is 360 mV; and η is 0.5%; which improved to: 7.2 mA/cm2, 485 mV and 1.7%, respectively, after heating the cell in forming gas. A cell with an Sb2S3 (40 nm) thin film as an antireflective coating on Bi2S3, produced: Jsc of 10 mA/cm2; Voc of 480 mV; and η of 2.4%. Theoretical simulation suggests that better cell fabrication could lead to: Jsc of 26 mA/cm2; Voc of 600 mV; and η of 10%.