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

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(oc)s of MoS2/p-Si solar cells improved by & SIM;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.