Passivation of grain boundary electronic activity in polycrystalline silicon thin films by heat treatment and hydrogenation

The polycrystalline silicon (poly-Si) thin films are widely used in photovoltaic applications. However, the main drawback is the electronic activity of the grain boundaries which affects the performance of solar cells based on this material. In order to reduce the impact of this phenomenon, which affects the photovoltaic conversion efficiency, heat treatments before doping and annealing under hydrogen were carried out on phosphorus-doped poly-Si thin films. The obtained results showed that the heat treatments before doping allow an improvement in the free carriers concentration of 15 to 55% for temperatures ranging from 1000 to 1150 & DEG;C. In addition, an increase in the carriers mobility and a reduction in the resistivity of the studied thin films were observed. On the other hand, the annealing under hydrogen allowed an improvement of 10 to 18% on the free carriers concentration, a reduction of the resistivity, and an increase of the carriers mobility. Therefore, it can be deduced that heat treatments followed by annealing under hydrogen allow the passivation of the grain boundaries and thus lead to an improvement of the electrical characteristics, and consequently, the efficiency of solar cells made from poly-Si thin films.

Automated summary

The electronic activity of grain boundaries in polycrystalline silicon (poly-Si) thin films hinders the performance of solar cells. Heat treatments before doping and annealing under hydrogen were found to enhance the free carriers concentration, carriers mobility, and reduce the resistivity of phosphorus-doped poly-Si thin films. This research suggests that these treatments can passivate the grain boundaries and improve the electrical characteristics and efficiency of poly-Si thin film solar cells.