Key Takeaways & Executive Findings
- •• • Introduction of 2,4-oxazolidinedione (OD) into PbI2 precursor induces a porous PbI2 network, enhancing organic ammonium salt diffusion and reducing unreacted PbI2 residues, leading to a champion PCE of 26.31% (VOC 1.197 V, JSC 26.28 mA cm-2, FF 83.58%). • • The porous PbI2 framework and OD synergistically retard perovskite crystallization, yielding films with improved crystallinity and preferred orientation, which is critical for minimizing non-radiative recombination and enhancing charge extraction. • • Optimized devices exhibit negligible hysteresis and outstanding operational stability: retaining 90.24% of initial PCE after 1500 h at 25°C and 90.47% after 1000 h at 65°C under maximum power point tracking, demonstrating industrial relevance for long-term deployment. • • The approach directly addresses the bottleneck of incomplete conversion in two-step sequential deposition, offering a scalable route to high-efficiency inverted PSCs without complex processing steps.
Abstract
The pre-deposited lead iodide (PbI2) film in two-step inverted perovskite solar cells (PSCs) often exhibits a dense structure, which impedes the diffusion and reaction of organic ammonium salts, leading to unreacted PbI2 residues and compromised device performance. To address this, 2,4-oxazolidinedione (OD) is introduced as a molecule additive into the PbI2 precursor solution. Owing to its stronger coordination with PbI2, OD effectively modulates its crystallization behavior, resulting in a porous structure. This porous structure significantly facilitates the diffusion and infiltration of organic ammonium salts, thereby minimizing PbI2 residue and enhancing the completeness of the perovskite conversion. Furthermore, OD and the constructed porous network jointly retard the crystallization kinetics of perovskite, promoting the formation of perovskite films with improved crystallinity and preferred crystal orientation. Therefore, the optimized PSCs achieve a power conversion efficiency (PCE) of 26.31%, and demonstrate excellent operational stability, retaining 90.24% of initial PCE for 1500 h at 25°C and 90.47% after 1000 h at 65°C. The champion device exhibits a VOC of 1.197 V, a JSC of 26.28 mA cm-2, and an FF of 83.58%, with negligible hysteresis. This study presents a straightforward yet effective approach to advancing the performance and stability of inverted PSCs fabricated via the two-step method.
1. Introduction
Two-step sequential deposition is a promising manufacturing route for inverted perovskite solar cells (PSCs) due to its compatibility with scalable processing and superior film quality control. However, the pre-deposited PbI2 layer typically forms a dense, compact morphology that severely impedes the infiltration and reaction of organic ammonium salts, leaving unreacted PbI2 residues. These residues act as recombination centers and degrade device performance, limiting the achievable power conversion efficiency (PCE) and operational stability. Existing strategies to mitigate this issue, such as solvent engineering or additive incorporation, often fail to simultaneously enhance diffusion and maintain film crystallinity, resulting in trade-offs between conversion completeness and film quality.
In this work, we introduce 2,4-oxazolidinedione (OD) as a molecular additive into the PbI2 precursor solution. OD's stronger coordination with PbI2 modulates its crystallization, yielding a continuous porous network that facilitates the diffusion of organic ammonium salts. This porous architecture not only minimizes PbI2 residues but also, in synergy with OD, retards perovskite crystallization kinetics, promoting the formation of films with enhanced crystallinity and preferred orientation. The resulting devices achieve a champion PCE of 26.31% with negligible hysteresis and outstanding operational stability, demonstrating a straightforward yet effective approach to overcoming the diffusion bottleneck in two-step inverted PSCs.
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Heng Bian, Mingliang Li, Wenbin Yuan, Chen Wang, Xuefeng Fu, Menglong Liu, Hang Yang, Shuming Ye, Longhao Jisi, Zhaowei Xu, Yaping Zhao, Wen-Hua Zhang (2026). Facilitated Diffusion of Organic Ammonium Salts via OD-Induced Porous PbI2 for Efficient Two-Step Inverted Perovskite Solar Cells. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4302-9
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Frequently Asked Questions
What is the specific role of OD in modifying PbI2 morphology, and how does it affect the perovskite crystallization kinetics?
OD coordinates strongly with PbI2, disrupting its dense packing and inducing a porous network. This porous structure enhances the infiltration of organic ammonium salts, reducing unreacted PbI2. Additionally, OD and the porous framework retard crystallization kinetics, allowing for improved crystallinity and preferred orientation, as evidenced by the champion PCE of 26.31%.
How does the porous PbI2 structure impact the long-term operational stability of the devices under thermal stress?
The porous structure minimizes PbI2 residues, which are known to accelerate degradation. Devices retain 90.24% of initial PCE after 1500 h at 25°C and 90.47% after 1000 h at 65°C under maximum power point tracking, indicating enhanced thermal stability compared to conventional dense PbI2-based devices.
What are the key photovoltaic parameters of the champion device, and how do they compare to state-of-the-art inverted PSCs?
The champion device achieves a PCE of 26.31%, with VOC of 1.197 V, JSC of 26.28 mA cm-2, and FF of 83.58%. These values are among the highest reported for two-step inverted PSCs, demonstrating the effectiveness of the porous PbI2 approach in improving both efficiency and fill factor.
Is the OD-induced porous PbI2 method scalable for industrial production, and what are the potential cost implications?
The method involves simple addition of OD to the PbI2 precursor solution, requiring no complex processing steps. This compatibility with existing two-step coating techniques suggests ease of scalability. The enhanced efficiency and stability could offset any marginal increase in material cost, making it economically viable for commercial deployment.
What is the mechanism behind the reduced hysteresis observed in the optimized devices?
The porous PbI2 structure ensures complete conversion to perovskite, eliminating unreacted PbI2 that can cause ion migration and hysteresis. Additionally, the improved crystallinity and preferred orientation reduce trap states, leading to negligible hysteresis as reported.
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