Improved Photovoltaic Performance of Si Nanowire Solar Cells Integrated with ZnSe Quantum Dots

Abstract

Introducing a ZnSe quantum dot (QD) layer over silicon nanowire (Si NW) solar cells considerably enhances external quantum efficiency (EQE) over broadband wavelengths. This is attributed to the combination of two major benefits of ZnSe QDs: superior light trapping and photon down-conversion. The integration of ZnSe QDs on the Si NW solar cell significantly reduces Fresnel reflection at the silicon/air interface because the refractive index of ZnSe QDs falls between those of Si and air. As a result, the refractive index mismatch at the interface can be alleviated. This decreases the Si NW length required for obtaining superior light absorption over 90%, which consequently leads to a substantial reduction in surface recombination loss. A remarkable enhancement of ∼30% in EQE around the absorption maximum of ZnSe QDs reveals that photon down-conversion by ZnSe QDs significantly contributed to EQE enhancement in a short-wavelength region. Our Si NW/ZnSe QDs hybrid solar cell showed nearly 13% improvement in power conversion efficiency compared to that of a bare Si NW counterpart, highlighting the feasibility of thin-layered semiconductor nanoparticles as a booster for highly efficient Si solar cells.