Enhanced efficiency and current density of solar cells via energy-down-shift having energy-tuning-effect of highly UV-light-harvesting Mn2+-doped quantum dots

Abstract

Enhancing the efficiency of solar cells via quantum dots (QDs) as an energy-down-shift (EDS) layer is a new approach to utilize the wasted energy in the ultra-violet (UV)-light, but the smaller Stokes shift in QDs leads towards partial self-re-absorption losses among QDs due to which the overall enhancement is limited. Here, Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell QDs were deposited as an EDS with a higher Stokes shift on the front surface of monocrystalline p-type silicon (mc-p-Si) solar cells through straightforward and cost-effective spin-coating technique. The Mn2+:Cd0.5Zn0.5S/ZnS QDs confirmed a typical EDS (2.76–4.96 eV → 2.13 eV), which absorb UV light in the range of 250–450 nm and emit visible yellow-orange light at 583 nm. Application of these QDs into the mc-p-Si solar cells clearly exhibited a larger Stokes shift (>200 nm), generated through a functional energy tuning effect (ETE) of Mn2+ dopant. Through this EDS having an ETE (EDS/ETE) QDs, a remarkable enhancement of the external-quantum-efficiency (EQE) in the UV region was observed. The EQE was improved by ~22.5% in the wavelength range of 300–450 nm and the short-circuit-current-density was enhanced about 1.42 mA/cm2 (+4.02%), which are the highest records reported so far. In particular, the power-conversion-efficiency was improved by ~3.22%, compared to its reference value recorded in the absence of an EDS/ETE QD layer. These results suggested that the Mn2+-doped QDs played a significant role in improving the efficiency and current density of solar cells.