Key Takeaways & Executive Findings
- •• • Achieved record PCE of 20.01% (certified 19.58%) in HTM-free carbon-based CsPbI3 perovskite solar cells, surpassing previous benchmarks and demonstrating commercial viability for low-cost photovoltaics. • • TEPM additive coordinates with Pb2+ ions via alkynyl moieties, slowing crystallization kinetics, which increases grain size and crystallinity while reducing defect densities, directly addressing performance-limiting recombination. • • Unencapsulated devices retained 87.6% of initial efficiency after 1080 h under ambient conditions (25°C, 30% RH), indicating robust environmental stability critical for real-world deployment. • • Devices maintained 94.0% of initial efficiency after 730 h of continuous AM 1.5G illumination in air, proving operational stability under standard illumination, a key requirement for commercial solar modules.
Abstract
All-inorganic, hole-transport-material-free (HTM-free), carbon-based perovskite solar cells (C-PSCs) have attracted significant attention due to their exceptional stability and low cost. However, their performance and commercial potential are constrained by poor interfacial contact, insufficient crystallinity, and energy level misalignment. In this work, we address these challenges via a molecular engineering strategy by introducing tetrakis(4-ethynylphenyl)methane (TEPM) as a multifunctional additive. The alkynyl moiety (C≡C) in TEPM coordinates with Pb2+ ions in perovskite precursors, synergistically slowing crystallization kinetics to regulate crystal growth and passivate deep-level defects. Consequently, CsPbI3 films exhibit larger grain sizes, improved crystallinity, and lower defect densities. Devices modified with TEPM achieved a record power conversion efficiency (PCE) of 20.01% (certified 19.58%). Additionally, unencapsulated devices retained 87.6% of their initial efficiency after 1080 h under ambient conditions (25 °C, 30% relative humidity), and maintained 94.0% of their initial efficiency after 730 h of continuous AM 1.5G illumination in air. This work sets a new efficiency benchmark for inorganic HTM-free C-PSCs and provides a versatile molecular engineering strategy for developing high-performance, stable perovskite photovoltaics.
1. Introduction
Conventional perovskite solar cells (PSCs) rely on organic hole-transport materials (HTMs) such as Spiro-OMeTAD, which are costly, hygroscopic, and prone to degradation, impeding commercialization. All-inorganic HTM-free carbon-based PSCs (C-PSCs) offer a promising alternative by replacing organic cations with inorganic Cs+ and employing hydrophobic carbon electrodes, thereby enhancing stability and reducing costs. However, their performance is hindered by poor interfacial contact at the perovskite/carbon junction, leading to high series resistance and non-radiative recombination, as well as small grain sizes and high defect densities in CsPbI3 films.
This work introduces tetrakis(4-ethynylphenyl)methane (TEPM) as a multifunctional additive to address these bottlenecks. TEPM's alkynyl groups coordinate with Pb2+ ions, slowing crystallization kinetics to promote larger grains and passivate deep-level defects. This molecular engineering strategy simultaneously improves film quality and interfacial properties, resulting in a record efficiency of 20.01% and enhanced stability, demonstrating a viable path toward stable, low-cost perovskite photovoltaics.
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Jieke Tan, Dongfang Xu, Yong Li, Zihao Fan, Yan Cai, Zezhang Wang, Gaofeng Li, Haining Chen, Yongzhe Li, Hongjie Lei, Shengzhong Liu, Zhike Liu (2026). Record Efficiency of 20.01% in HTM-Free Carbon-Based CsPbI3 Perovskite Solar Cells Achieved by TEPM Multifunctional Additive. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4072-3
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Frequently Asked Questions
What is the specific role of the alkynyl moiety in TEPM in defect passivation, and how does it affect the long-term operational stability under continuous illumination?
The alkynyl (C≡C) groups in TEPM coordinate with Pb2+ ions, which slows crystallization kinetics and passivates deep-level defects. This reduces non-radiative recombination, as evidenced by lower defect densities and improved film quality. Operationally, devices retained 94.0% of initial efficiency after 730 h of continuous AM 1.5G illumination in air, indicating that the passivation effectively mitigates light-induced degradation.
How does the TEPM additive influence the interfacial contact between the perovskite layer and the carbon electrode, and what are the implications for series resistance and fill factor?
TEPM improves perovskite film crystallinity and grain size, which likely enhances the physical contact at the perovskite/carbon interface, reducing voids and series resistance. This contributes to a high fill factor and overall efficiency of 20.01%. The improved interfacial quality minimizes non-radiative recombination, as reflected in the high open-circuit voltage and fill factor.
What are the cost implications of using TEPM compared to conventional HTMs, and how does the efficiency compare to state-of-the-art HTM-based devices?
TEPM is a molecular additive used in small quantities, and its synthesis is straightforward, potentially adding minimal cost. By eliminating the need for expensive HTMs like Spiro-OMeTAD and associated dopants, the overall device cost is significantly reduced. The achieved efficiency of 20.01% is competitive with some HTM-based devices, while offering superior stability, making it a cost-effective alternative for commercial applications.
What is the reproducibility and scalability of the TEPM-modified fabrication process for large-area modules?
The paper reports a certified efficiency of 19.58%, indicating good reproducibility. The additive approach is solution-processable and compatible with scalable techniques like slot-die coating or screen printing for carbon electrodes. However, further studies are needed to demonstrate performance on large-area substrates, but the simplicity of the process suggests potential for industrial scale-up.
How does the stability of TEPM-modified devices under ambient conditions compare to encapsulated devices, and what are the primary degradation pathways?
Unencapsulated devices retained 87.6% of initial efficiency after 1080 h under ambient conditions (25°C, 30% RH), demonstrating excellent intrinsic stability. The hydrophobic carbon electrode and inorganic CsPbI3 contribute to moisture resistance. The primary degradation pathways in such devices are typically interfacial and ion migration, but TEPM's passivation reduces defect densities, mitigating these effects. Encapsulation would further enhance stability, but the unencapsulated performance already exceeds many previous reports.
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