Homogeneously Blended Donor and Acceptor AgBiS2 Nanocrystal Inks Enable High‐Performance Eco‐Friendly Solar Cells with Enhanced Carrier Diffusion Length

Surface trap sites in AgBiS₂ nanocrystals (NCs) cause trap-assisted recombination and short diffusion lengths, decreasing power conversion efficiency (PCE) in photovoltaic applications. This study presents a donor–acceptor blended solar cell with tailored surface chemistry, which promotes carrier separation, extends carrier lifetime and diffusion lengths, and improves PCE to 8.26%.

Abstract

Colloidal semiconductor nanocrystals (NCs) have garnered significant attention as promising photovoltaic materials due to their tunable optoelectronic properties enabled by surface chemistry. Among them, AgBiS₂ NCs stand out as an attractive candidate for solar cell applications due to their environmentally friendly composition, high absorption coefficients, and low-temperature processability. However, AgBiS₂ NC photovoltaics generally exhibit lower power conversion efficiency (PCE) compared to other NC-based devices, primarily due to numerous surface traps that serve as recombination sites, leading to a short diffusion length for free carriers. To address this challenge, this work develops donor and acceptor blended (D/A) AgBiS₂ films. Through ligand modulation, this work formulates acceptor and donor AgBiS₂ NC inks with suitable electrical band alignment for charge separation, while ensuring that they are fully miscible in the same solvent. This enabled the fabrication of high-quality, thickness-controllable D/A-blended junction films. This work finds that this approach effectively facilitates carrier separation, leading to an enhanced carrier lifetime and diffusion length. As a result, using this approach, this work achieves AgBiS₂ films that are twice as thick in solar cell applications compared to conventional devices, leading to improvements in current density and a solar cell PCE of 8.26%.