# Intermediate Bandgap (IB) Cu3VSxSe4−x Nanocrystals as a New Class of Light Absorbing Semiconductors

## TL;DR

Researchers developed new nanocrystals with tunable bandgaps that could improve solar cell efficiency by absorbing more light.

## Contribution

The study introduces a new class of IB Cu3VSxSe4−x nanocrystals with tunable bandgaps and high crystallinity for solar cell applications.

## Key findings

- CVSSe nanocrystals exhibit tunable optical bandgaps spanning visible and near-infrared ranges.
- High crystallinity and uniform size of nanocrystals were confirmed via microscopy techniques.
- A current conversion efficiency of 14.7% was achieved with Cu3VS4, suggesting potential for solar cells beyond the Shockley–Queisser limit.

## Abstract

A new family of highly uniform, cubic-shaped Cu3VSxSe4−x (CVSSe; 0 ≤ x ≤ 4) nanocrystals based on earth-abundant materials with intermediate bandgaps (IB) in the visible range is reported, synthesized via a hot-injection method. The IB transitions and optical band gap of the novel CVSSe nanocrystals are investigated using ultraviolet-visible spectroscopy, revealing tunable band gaps that span the visible and near-infrared regimes. The composition-dependent relationships among the crystal phase, optical band gap, and photoluminescence properties of the novel IB semiconductors with progressive substitution of Se by S are examined in detail. High-resolution transmission electron microscopy and scanning electron microscopy characterization confirm the high crystallinity and uniform size (~19.7 nm × 17.2 nm for Cu3VS4) of the cubic-shaped nanocrystals. Density functional theory (DFT) calculations based on virtual crystal approximation support the experimental findings, showing good agreement in lattice parameters and band gaps across the CVSSe series and lending confidence that the targeted phases and compositions have been successfully realized. A current conversion efficiency, i.e., incident photon-to-current efficiency, of 14.7% was achieved with the p-type IB semiconductor Cu3VS4. These novel p-type IB semiconductor nanocrystals hold promise for enabling thin film solar cells with efficiencies beyond the Shockley–Queisser limit by allowing sub-band-gap photon absorption through intermediate-band transitions, in addition to the conventional direct-band-gap transition.