Ammonia Borane All-In-One Modification Strategy Enables High-Performance Perovskite Solar Cells

Abstract

Perovskite solar cells have achieved remarkable progress in photovoltaic efficiency. However, interfacial defects at the buried and upper interfaces of perovskite layer remain a critical challenge, leading to charge recombination, ion migration, and iodine oxidation. To address this, we propose a novel all-in-one modification strategy employing ammonia borane (BNH6) as a multifunctional complex. By incorporating BNH6 at both buried and upper interfaces simultaneously, we achieve dual-interfacial defect passivation and iodide oxidation suppression through three key mechanisms: (1) hydrolysis-induced interaction with SnO2, (2) coordination with Pb2+, and (3) inhibition of I− oxidation. This approach significantly enhances device performance, yielding a champion power conversion efficiency (PCE) of 26.43% (certified 25.98%). Furthermore, the unencapsulated device demonstrates prominent enhanced operation stability, maintaining 90% of its initial PCE after 500 h under continuous illumination. Notably, our strategy eliminates the need for separate interface treatments, streamlining fabrication and offering a scalable route toward high-performance perovskite photovoltaics.

1. Introduction

Organic–inorganic hybrid perovskite solar cells (PSCs) have become one of the most attractive fields due to their excellent optoelectronic properties [1–5]. The power conversion efficiency (PCE) of PSCs has rapidly reached 27.0% in the past few years [6–8]. This continuous progress is attributed to various attempts, including bandgap modulation [9–11], crystallization behavior regulation [12–17], and interface modification [18–27]. The low-temperature solution method is prevalent for preparing state-of-the-art PSCs. However, perovskite films prepared through such rapid low-temperature approach are liable to generate large numbers of interfacial defects, which serve as nonradiative recombination centers to hinder charge transport [28–31].

To address this, various strategies have been explored. For example, Yi et al. employed 1-[3-(Trimethoxysilyl)propyl]urea (TMPU) at SnO2/perovskite interface and trimethoxy (3,3,3-trifluoropropyl)silane (TMFS) at perovskite/Spiro-OMeTAD interface to passivate detrimental interface defects and facilitate faster carrier extraction [32]. Zheng et al. reported a strategy to dense the hole transport layer (HTL) by introducing (aminomethyl)phosphonic acid (AMP) into the precursor solution, concurrently modifying the top surface of the perovskite with 2-(3-fluorophenyl)ethylamine iodide (mF-PEAI) and piperazinium diiodide (PDI) [33]. These effective interface modification strategies are summarized in Table S1. However, the applying of excessive types of additives is unfavorable to the rapid device manufacturing, as well as the commercial fabrication.

Besides, iodide ions (I−) in the perovskite layer can migrate under the influence of environmental factors due to their lower formation energy [34]. This migration can lead to an uneven ion distribution at the interfaces, and the accumulation of iodine ions at the interfaces may induce adverse redox reactions, which frequently involve the generation of iodine defects (I0) [35–37]. I0 is volatile and can easily escape from the perovskite layer, accelerating the degradation of perovskite. Nevertheless, only a few additives were used to address this issue, such as benzylhydrazine hydrochloride (BHC) [38], the redox pairs of Eu3+-Eu2+ [35], and fluoroN,N,N″,N″-tetramethylformamidinium hexafluorophosphate (TFFH) [39], serving as reducing agents effectively reduced I0 back to I−. In spite of these attempts have been made in improving the performance of PSCs, these works are all achieved by improving the stability of perovskite precursor solutions. However, when perovskite film is exposed to ambient environment, further challenges arise.