reflection, scattering, and thermalization losses, which limit conversion efficiency. [10] These losses are mostly caused by the energy difference between the incident UV photons (>3.2 eV) and bandgap of PV cells (1.0-1.6 eV). [11] If these photons are not surface reflected, their excess energy will be adversely dissipated in cells as heat via the nonradiative relaxation of the photoexcited electronhole pairs leading to further limitations and faster degradation of PV cells. [12] One of the most promising approaches to overcome these limitations is to implement the surfaces of PV devices with an energydownshift quantum-dot (EDS-QD) layer to harvest the wasted UV photons and reemit them at visible wavelengths absorbed more efficiently by PV cells. [13] Moreover, EDS-QDs have been well demonstrated as an effective layer that boosts the energy density, then the usage active area of PV cells could be reduced by the same percentage of enhancement in PV efficiency for a defined amount of power. Due to the enhanced efficiency along with the low cost of preparing EDS-QDs, the cost of PV electricity generation could be effectively minimized. [1d,14] For the abovementioned reasons, the concept of the EDS-QD layer was proposed for solar energy conversion for both increasing the efficiency and lessening the cost.Motivated by these purposes and attracted by their excellent optical properties, Cd-based core/shell QDs, such as CdSe/ CdS, [13c,15] CdSe/CdZnS, [16] CdSe/ZnS, [11b] and Cd 0.5 Zn 0.5 S/ ZnS [13b,17] QDs have been used recently as EDS layers. However, the relying on the Cd-based QDs in commercial solar cells has been limited due to two main reasons; the toxicity of Cd metal ions [18] and the self-reabsorption losses within their QDs. [13a] For the latter, Mn-doped Cd 0.5 Zn 0.5 S/ZnS QDs have been introduced more recently [13a,14a] as an excellent EDS-QD layer having free-self-reabsorption with large Stokes shift, yet with environmentally hazardous Cd material. [19] As a result, the quest for nontoxic high photoluminescence-quantum yield (PLQY) and the zero-self-reabsorption EDS-QD layer is a priority for their commercial applications.Alternatively, chalcogenide CIGS is one of the most promising semiconductor materials for EDS-QD layers due to its beneficial properties of large absorption coefficient (10 5 cm −1 ), [20] eco-friendly nature, [19,21] long-term stability, [22] It is presented for the first time nontoxic CuGaS 2 /ZnS quantum dots (QDs) with free-self-reabsorption losses and large Stokes shift (>190 nm) synthesized on an industrially gram-scale as an alternative for Cd-based energydownshift (EDS)-QD layers. The QDs exhibit a typical EDS that absorbs only UV light (<407 nm) and emits the whole range of visible light (400-800 nm) with a high photoluminescence-quantum yield of ≈76%. The straightforward application of these EDS-QDs on the front surface of a monocrystalline p-type silicon solar cell significantly enhances the short-circuit current density by ≈1.64 mA cm −2 (+4.20%); thereby, improving ...
