Composition Related Tunability of “Green” Core/Shell Quantum Dots for Photovoltaic Applications from First Principles

Abstract

Quantum dots (QDs) with core/shell (c/s) type configurations are promising candidates for photovoltaic (PV) applications, as they are known to enhance the QD stability, and are also expected to reduce charge carrier recombination both by reducing the trap states and increasing charge carrier separation. Hence, here we report detailed first-principles studies of different compositions of c/s QDs made from nontoxic materials, namely, CuInSe2/ZnS, CuInSe2/ZnSe, and CuInSe2/CuInS2 and their inverts, namely, ZnS/CuInSe2, ZnSe/CuInSe2, and CuInS2/CuInSe2. The geometric and electronic properties are studied using first-principles density functional theory (DFT). The optimized structures of all the QDs were found to have a defect-free c/s interface, which would reduce charge-carrier recombination rates arising due to charge trapping. The projected density of states (PDOS) of the QDs shows that the highest occupied molecular orbital (HOMO) is mainly composed of either S or Se states, whereas Zn or In states constitute the lowest unoccupied molecular orbital (LUMO). Time-dependent DFT (TDDFT) calculations of the optical transitions show that these systems have a strong absorption in the visible region of the spectrum. Interestingly, the c/s configuration enables the tailoring of the electronic and optical properties compared to the bulk as well as QD systems; as in the c/s QDs, the relative thickness as well as material composition of the core and shell is also a tunable parameter, in addition to the QD size. A natural transition orbital (NTO) analysis of the charge transfer upon light absorption shows, surprisingly, that charge separation occurs only in certain c/s configurations, such as the CuInSe2/ZnS QD, via fast direct electron transfer from core to shell, and CuInSe2/ZnSe QD, via indirect electron transfer, which may be slower. Hence, these compositions are expected to exhibit better efficiencies for PV applications. Thus, our study also highlights the importance of the NTO analysis in giving a detailed insight into local excitations and charge transfer excitations in these promising systems.

Heteroleptic Cu(i) bis-diimine complexes as sensitizers in dye-sensitized solar cells (DSSCs): on some factors affecting intramolecular charge transfer

“…5) functionals respectively for the dyes considered in our study. These results are consistent with our earlier results for “green” core/shell quantum dots 37 and with other theoretical studies in the literature, 38–40 showing that B3LYP under-estimates the HOMO–LUMO gap, while CAM-B3LYP over-estimates it. The HOMO–LUMO gaps of dmp based dyes are slightly larger than dpbpy dyes when computed with both exchange–correlation functionals (Fig.…”

“…NTOs provide an understanding of the charge distribution and transfer upon optical excitation of the dye, which is useful for determining the efficacy of new dyes for solar cell applications. 27,[35][36][37] 3 Results and discussion…”

Peroxidase-Mimicking Ir-Te Nanorods for Photoconversion-Combined Multimodal Cancer Therapy

“…Depending on the composition, the indirect properties imparted by the inner constituent elements and the direct surface properties imparted by the outer shell constituent parts can exhibit a synergistic effect. As previously described for core-shell nanoparticles, the strata-specific morphology with a few nanometer-scale shells maintains the properties of a metallic core composition while simultaneously incorporating the properties of a shell composition [1][2][3][4][5]. Galvanic replacement is a promising technique for incorporating additional elements into the metal nanoparticle template.…”

Morphological evolution of individual microrods to self-assembled 3D hierarchical flower architectures of CuBixIn1−xSe2 for photo response applications

“…3 Similarly, core/shell quantum dots CIS/Zn(S,Se) and corresponding inverts exhibited efficiencies suitable for photovoltaic (PV) applications due to local excitation and charge transfer excitation. 4 Composition variation is one of the promising approaches for achieving controllable properties, greater efficiencies, and stability. In this regard, CuIn x Ga 1− x Se 2 (CIGS), CuIn 1− x Fe x Se 2 (CIFS), and CuIn 1− x Al x Se 2 (CIAS) are well-known alternative semiconductors containing Ga, Fe, and Al, respectively, in place of In to enhance PV efficiency and different property tuning.…”