<title>Chemically deposited thin films of sulfides and selenides of antimony and bismuth as solar energy materials</title>

Abstract

Chemical bath deposition techniques for bismuth sulfide, bismuth selenide, antimony sulfide, and antimony selenide thin films of about 0.20 - 0.25 micrometer thickness are reported. All these materials may be considered as solar absorber films: strong optical absorption edges, with absorption coefficient, (alpha) , greater than 10<SUP>4</SUP> cm<SUP>-1</SUP>, are located at 1.31 eV for Bi<SUB>2</SUB>Se<SUB>3</SUB>, 1.33 eV for Bi<SUB>2</SUB>S<SUB>3</SUB>, 1.8 eV for Sb<SUB>2</SUB>S<SUB>3</SUB>, and 1.35 eV for Sb<SUB>2</SUB>Se<SUB>3</SUB>. As deposited, all the films are nearly amorphous. However, well defined crystalline peaks matching bismuthinite (JCPDS 17- 0320), paraguanajuatite (JCPDS 33-0214), and stibnite (JCPDS 6-0474) and antimony selenide (JCPDS 15-0861) for Bi<SUB>2</SUB>S<SUB>3</SUB>, Bi<SUB>2</SUB>Se<SUB>3</SUB>, Sb<SUB>2</SUB>S<SUB>3</SUB> and Sb<SUB>2</SUB>Se<SUB>3</SUB> respectively, are observed when the films are annealed in nitrogen at 300 degrees Celsius. This is accompanied by a substantial modification of the electrical conductivity in the films: from 10<SUP>-7</SUP> (Omega) <SUP>-1</SUP> cm<SUP>-1</SUP> (in as prepared films) to 10 (Omega) <SUP>-1</SUP> cm<SUP>-1</SUP> in the case of bismuth sulfide and selenide films, and enhancement of photosensitivity in the case of antimony sulfide films. The chemical deposition of a CuS/Cu<SUB>x</SUB>Se film on these V<SUB>x</SUB>- VI<SUB>y</SUB> films and subsequent annealing at 300 degrees Celsius for 1 h at 1 torr of nitrogen leads to the formation of p-type films (conductivity of 1 - 100 (Omega) <SUP>-1</SUP> cm<SUP>-1</SUP>) of multinary composition. Among these, the formation of Cu<SUB>3</SUB>BiS<SUB>3</SUB> (JCPDS 9-0488) and Cu<SUB>3</SUB>SbS<SUB>4</SUB> (JCPDS 35- 0581), CuSbS<SUB>2</SUB> (JCPDS 35-0413) have been clearly detected. Solar energy applications of these films are suggested.