Investigation of absorber and heterojunction in the pure sulphide kesterite

Abstract

This paper aims to study the properties of the absorber layer and the heterojunction in kesterite solar cells. The Cu2ZnSnS4 (CZTS) thin films were layered on a glass substrate from a colloidal solution of metal salts and thiourea dissolved in a mixture of water and ethanol and deposited by spin coating technique. The samples were then heat treated in a furnace, in the presence of sulphur powder and under a nitrogen gas flow. The results revealed the formation of homogeneous layers of a pure kesterite phase of CZTS crystallites after heat treatment with correct stoichiometry and oxidation states. The optical transmission measurements indicate an energy band-gap of 1.4eV and an absorption coefficient of 104cm−1. These CZTS thin films, elaborated by spin coating process, were integrated for electronic properties evaluation in a heterojunction in the following configuration: SnO2:F (FTO) and Molybdenum as back contact, CdS as tampon and the CZTS film as absorber layer. The band alignment at the CdS–CZTS heterojunction indicates a cliff-like conduction band offset (CBO) even close to be a flat band.