Thermally Driven Point Defect Transformation in Antimony Selenosulfide Photovoltaic Materials

Abstract

Thermal treatment of inorganic thin films is a general and necessary step to facilitate crystallization and, in particular, to regulate the formation of point defects. Understanding the dependence of the defect formation mechanism on the annealing process is a critical challenge in terms of designing material synthesis approaches for obtaining desired optoelectronic properties. Herein, a mechanistic understanding of the evolution of defects in emerging Sb2(S,Se)3 solar cell films is presented. A top‐efficiency Sb2(S,Se)3 solar‐cell film is adopted in this study to consolidate this investigation. This study reveals that, under hydrothermal conditions, the as‐deposited Sb2(S,Se)3 film generates defects with a high formation energy, demonstrating kinetically favorable defect formation characteristics. Annealing at elevated temperatures leads to a two‐step defect transformation process: 1) formation of sulfur and selenium vacancy defects, followed by 2) migration of antimony ions to fill the vacancy defects. This process finally results in the generation of cation–anion antisite defects, which exhibit low formation energy, suggesting a thermodynamically favorable defect formation feature. This study establishes a new strategy for the fundamental investigation of the evolution of deep‐level defects in metal chalcogenide films and provides guidance for designing material synthesis strategies in terms of defect control.

A comprehensive insight into deep-level defect engineering in antimony chalcogenide solar cells

“…To intuitively assess the influence of individual types of deep-level defects on the device performance, the ( σ · N T ) −1 values are evaluated and compared. According to the trap-assisted-SRH recombination model, the τ SRH value associated with a specific defect depends on the carrier thermal velocity ( v th ), capture cross section ( σ ), and trap density ( N T ), as follows: 49,50 Deep-level transient spectroscopy (DLTS), thermally stimulated current (TSC), and admittance spectroscopy are the most frequently used techniques for characterizing defects in semiconductors. 51 In general, TSC is limited by its low sensitivity, shallow detection depth, and complicated operation.…”

“…Che et al 49 investigated the influence of the annealing process on the defect formation mechanism in hydrothermally deposited n-type Sb 2 (S,Se) 3 films. High-temperature annealing (200–425 °C) led to a two-step defect transformation process, i.e.…”

“…18,31 To intuitively assess the influence of individual types of deeplevel defects on the device performance, the (sÁN T ) À1 values are evaluated and compared. According to the trap-assisted-SRH recombination model, the t SRH value associated with a specific defect depends on the carrier thermal velocity (v th ), capture cross section (s), and trap density (N T ), as follows: 49,50…”

“…Che et al 49 investigated the influence of the annealing process on the defect formation mechanism in hydrothermally deposited n-type Sb 2 (S,Se) 3 films. High-temperature annealing (200-425 1C) led to a two-step defect transformation process, i.e., the formation of V Se /V S vacancy defects (with high formation energies), followed by the migration of Sb ions to fill the vacancy defects (forming antisite defects with low formation energies).…”

Negative-pressure sulfurization of antimony sulfide thin films for generating a record open-circuit voltage of 805 mV in solar cell applications

“…Che et al probed the evolution of deep-level defects during the annealing process to demonstrate the thermodynamically favorable defect formation feature of Sb 2 (S,Se) 3 . 21 The antimony ions occupying the anion vacancies facilitated by the loss of anions at low annealing temperatures formed cation/anion antisite defects in the annealed films. However, the high saturated vapor pressure of sulfur inevitably led to the loss of anions before the film crystallization.…”