Back contact modification in Sb₂Se₃ solar cells: The effect of a thin layer of MoSe₂

The record efficiency reported for Sb₂Se₃ solar cells is 9.2% and different lines of work have been opened with the aim of overcoming the factors that limit this value. Between them, the back contact is one of the aspects that must be considered to improve the efficiency of solar cells. In this work, the effect of forming an intermediate layer between the back contact of Mo and the Sb₂Se₃ absorber is studied and its impact on the properties of solar cells processed in substrate configuration: glass/Mo/Sb₂Se₃/CdS/i-ZnO/ITO, is evaluated. For the study, a series of photovoltaic devices were processed in which selenization processes were carried out in the molybdenum contact under different thermal annealing temperatures in the range of 320 to 400°C to produce the MoSe₂ compound. The influence of these thermal processes based on Sb₂Se₃ structural properties and the electro-optical properties of solar cells was evaluated. The results revealed that by the introduction of MoSe₂, through the selenization of the Mo, the electrical properties of the solar cells are improved, with the best efficiency solar cell of 5.0%. According to our analysis, it is considered that the optimization of the electrical parameters is a consequence of the behavior of MoSe₂ as a hole transport layer, giving rise to a n-i-p structure whose internal electrical field is found further within the absorber, which makes the carrier separation process more efficient and prevents recombination. On the other hand, to evaluate the thickness of the MoSe₂ layer and determine the physical processes that limit the efficiency of the devices, a simulation process was carried out based on the experimental results.