FAI-Induced Defect Passivation Significantly Boosts Performance of Spray-Deposited Lead-Free Cs3Bi2I9 Self-Powered Photodetectors

August 17, 2026

ACS Publications International Research

Overview

Formamidinium iodide (FAI) has been successfully utilized to passivate defects in spray-coated lead-free Cs3Bi2I9 (CBI) perovskite films, leading to dramatically enhanced structural and optical quality. This FAI treatment reduced defect states, improved crystallinity, and promoted secondary grain growth, resulting in superior charge transport and outstanding device performance in self-powered photodetectors. Optimized devices achieved a responsivity of 4.14 × 10–4 A W–1 and a detectivity of 1.73 × 1010 Jones under white light, demonstrating significant progress in eco-friendly optoelectronics.

In Depth

Background

The growing demand for environmentally friendly and sustainable materials has driven intensive research into lead-free perovskites for applications in solar cells and photodetectors, primarily due to their low toxicity. Among these, Cs3Bi2I9 (CBI) stands out as a promising bio-inspired, inorganic perovskite, free of toxic lead and thus an attractive candidate for next-generation optoelectronic devices. However, the performance of these eco-friendly materials has traditionally been constrained, often lagging behind their lead-based counterparts, particularly when fabricated using conventional methods. A key challenge lies in developing scalable, cost-effective manufacturing techniques that can produce high-quality films. Spray coating addresses this by offering a low-cost, high-throughput, and scalable method for depositing uniform thin films over large areas, ideal for industrial application, yet often posing its own set of material quality challenges.

Key Findings

Groundbreaking research has demonstrated that a novel defect passivation strategy using formamidinium iodide (FAI) dramatically enhances the performance of spray-coated, lead-free Cs3Bi2I9 (CBI) perovskite films. This FAI treatment fundamentally improves both the structural and optical quality of the films by selectively binding to crucial defect sites, such as halide vacancies and uncoordinated bismuth atoms, present on the surface and within the bulk of the perovskite crystals. This targeted passivation effectively suppresses non-radiative recombination and extends the lifetime of charge carriers, leading to a more ordered crystalline structure, improved grain size and orientation, and promoting secondary grain growth. The result is denser films with significantly enhanced light absorption efficiency and optimized charge transport. These improvements culminated in superior device performance for self-powered photodetectors. The optimized devices achieved a high responsivity of 4.14 × 10–4 A W–1 and an excellent detectivity of 1.73 × 1010 Jones under white light. Operating in a self-powered mode without an external bias, these photodetectors demonstrate impressive capabilities for applications ranging from imaging to environmental monitoring and optical communications. This FAI-induced defect passivation strategy represents a major breakthrough, establishing a crucial foundation for accelerating the commercialization of high-performance, lead-free perovskite photodetectors and opening pathways for their integration into sustainable electronics.

Source: https://pubs.acs.org/aaemcq/article/9/15/9886/5222552/FAI-Induced-Defect-Passivation-for-Enhanced

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