The effect of Al2O3 electrical shielding on MoS2 energy structure modulation in MoS2/p-Si heterojunction solar cells

Abstract

In this work, the authors utilize the electrical-shielding effect to change the electronic properties and energy structure of MoS₂ for enhancing the photovoltaic performance of MoS₂/p-Si solar cells. The ALD-Al₂O₃ thin film functions as a contact doping layer with MoS₂ to control its electron distribution and Fermi level through intrinsic negative charges. It was found that the electron density and mobility of MoS₂ both increased when Al₂O₃ was introduced. The Fermi level of the doped MoS₂ upshifted toward its valence band, decreasing the work function to 3.92 eV and enlarging the MoS₂/p-Si energy level splitting. After Al₂O₃ doping, the built-in field (V_bi) of the MoS₂/p-Si junction enhanced significantly to 610 mV, and the diffusion mechanism dominates the carrier transport process here. Under the synergistic effects of surface passivation and n-type doping of Al₂O₃, the V_ocs of MoS₂/p-Si solar cells improved by ∼26%. Besides, the lower reflectivity in the Al₂O₃/MoS₂ window layer leads to light absorption enhancement in a short wavelength and J_sc increasement in solar cells. Finally, we obtain an optimized bulk-like MoS₂-based solar cell with a conversion efficiency of 5.02% (V_oc 302.5 mV, J_sc 33.29 mA cm⁻², and FF 49.88%) by energy band engineering. The depth-UPS analysis and C–V fitting results revealed the nature of improvement of MoS₂/p-Si photovoltaic properties, where the electrons directionally transporting and accumulating in MoS₂ under electric fields caused by Al₂O₃ mainly influence the energy band alignment and p–n junction behavior at the MoS₂/Si interface.