Towards understanding poor performances in spray-deposited Cu₂ZnSnS₄ thin film solar cells

Cu₂ZnSnS₄ (CZTS) thin films deposited by spray pyrolysis technique are quite attractive for solar cell applications. However, low efficiency values have been achieved up to date. Among the different optoelectronic parameters, relatively low open-circuit voltage and short-circuit current density values are the common feature in sprayed-CZTS solar cells. Nevertheless, there is no report focused on explaining the main sources of such low performances. One of the most important parameters governing the behavior of a solar cell is minority carrier diffusion length. Furthermore, a transport mechanisms study is required to understand main recombination paths. In this work, sprayed-CZTS thin film solar cells are fabricated in order to study the main limiting factors regarding this technology. It is found that CZTS films are characterized by low minority carrier diffusion length values, emphasizing the need for improving sprayed-CZTS crystalline quality. Finally, current-voltage measurements at different temperatures for solar cell with maximum efficiency were carried out in order to find out the dominant transport mechanisms. It is discovered that tunneling enhanced recombination at junction interface gives a quantitative description of the electronic loss mechanisms in the sprayed-CZTS based heterojunction solar cells.