The effect of MoS2 modulated doping with molybdenum-oxide on the photovoltaic performance for MoS2/n-Si heterojunction solar cells

Abstract

Achieving large Fermi energy splitting under illumination is critical for improving the performance of photovoltaic devices. In this work, we conducted the energy band structure modulation of MoS2 thin films via MoOx doping scheme to realize its photovoltaic operation on n-type c-Si by magnetron sputtering. It is found that, by capping a MoOx overlayer, the MoS2 electrons density decreased and the Fermi level shifted ~0.4 eV towards valence band, consequently the MoS2 conductive type changing. With this doped MoS2 layer, the built-in electric field of fabricated MoS2/n-Si heterojunction devices greatly improved and exceeded 400 mV owing to the larger interface energy-level differences. Meanwhile, the defects recombination losses reduced benefiting from the holes-selective behavior of O-deficiencies in MoOx, so that the photo-generated carriers extraction process were promoted. As a result, the doped MoS2/n-Si devices showed excellent rectification behavior with rectifying ratio to 105 and ideality of 1.12. The TRPL spectrums corroborated the enhanced carrier transport mechanism at MoS2/n-Si interface by MoOx modulation doping effect. Correspondingly, the significant improvement of doped MoS2/n-Si solar cells performance (Voc of 289 mV, FF of 60.72% and Jsc of 31.25 mA/cm2) was achieved, exhibiting an optimized conversion efficiency of 5.47%. The UPS analysis revealed that the doping mechanism of MoOx/MoS2 stacks lies in energy band overlap and electrons contact transfer between these two materials. This observation of MoOx modulation doping effect on large-area sputtering MoS2 could help in building a better interface carrier transport in photovoltaic and optoelectronic applications of 2D materials.