Key Takeaways & Executive Findings
- •• The Ag/H co-doping strategy effectively suppresses SnZn-related defects and enhances the performance of CZTSSe solar cells. • Hydrogen incorporation improves the poor electrical conductivity and low carrier density caused by Ag substitution. • The synergistic effect of defect passivation and photoelectric property modulation leads to a champion efficiency of 14.74%. • This work provides a promising pathway for achieving high-efficiency kesterite-based photovoltaic devices.
Abstract
The presence of SnZn-related defects in Cu2ZnSn(S,Se)4 (CZTSSe) absorber results in large irreversible energy loss and extra irreversible electron–hole non-radiative recombination, thus hindering the efficiency enhancement of CZTSSe devices. Although the incorporation of Ag in CZTSSe can effectively suppress the SnZn-related defects and significantly improve the resulting cell performance, an excellent efficiency has not been achieved to date primarily owing to the poor electrical-conductivity and the low carrier density of the CZTSSe film induced by Ag substitution. Herein, this study exquisitely devises an Ag/H co-doping strategy in CZTSSe absorber via Ag substitution programs followed by hydrogen-plasma treatment procedure to suppress SnZn defects for achieving efficient CZTSSe devices. In-depth investigation results demonstrate that the incorporation of H in Ag-based CZTSSe absorber is expected to improve the poor electrical-conductivity and the low carrier density caused by Ag substitution. Importantly, the C=O and O–H functional groups induced by hydrogen incorporation, serving as an electron donor, can interact with under-coordinated cations in CZTSSe material, effectively passivating the SnZn-related defects. Consequently, the incorporation of an appropriate amount of Ag/H in CZTSSe mitigates carrier non-radiative recombination, prolongs minority carrier lifetime, and thus yields a champion efficiency of 14.74%, showing its promising application in kesterite-based CZTSSe devices.
1. Introduction
Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have emerged as promising candidates for next-generation thin-film photovoltaic technologies due to their incomparable advantages, such as low cost, high absorption coefficient, adjustable bandgap, and high theoretical conversion efficiency [1–5]. In the past decade, the certified power conversion efficiency (PCE) of CZTSSe devices has made incredible progress, soaring from 12.6% to over 15% [6, 7]. Even so, compared with its predecessors, including CIGS (23.6%), cadmium telluride (22.6%), and silicon (26.81%) solar cells [7–9], there is still a great gap. Therefore, it is imperative to explore the internal loss mechanism that affects the improvement of cell performance to chase high-performance CZTSSe devices.
It is generally recognized that the Shockley-Queisser (S-Q) theoretical limit efficiency of CZTSSe solar cells is 32.8%, which is a prediction of theoretical sunlight-to-electricity conversion efficiency of a single-junction solar cell based on the principle of detailed balance [10]. In reality, however, few materials approach this radiative limit. For single-junction CZTSe (CZTS) solar cells, its intrinsic limit efficiency is only 20.3% (20.9%), due to the presence of large irreversible energy loss and extra irreversible electron–hole non-radiative recombination [11, 12]. In this regard, suppressing the non-radiative recombination loss is imperative for the CZTSSe device performance to reach the S-Q theoretical limit. Encouragingly, recent theoretical calculations and experimental studies have proposed that the deep defects, such as SnZn donor and associated compensated defect clusters, in CZTSSe absorber bulk are often responsible for carrier trapping and non-radiative recombination owing to their high concentration (>10^14 cm^-3), which could result in a shorter carrier lifetime and a lower open-circuit voltage (VOC), limiting the performance of resulting devices [13–15].
In an attempt to address these issues, a number of studies have been conducted to suppress the formation of SnZn-related defects [1, 4, 16–21], and thus, to radically promote the VOC and PCE of CZTSSe solar cells. Some studies have shown that the proper isoelectronic cation substitution in the host CZTSSe crystal lattice is an effective method to address this issue [17, 18]. Other studies highlight the importance of local chemical environment engineering in suppressing detrimental intrinsic defects (i.e., SnZn) in CZTSSe devices [20, 21]. In particular, theoretical studies strongly indicate that substituting Cu with Ag for...
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Xiaoyue Zhao, Jingru Li, Chenyang Hu, Yafang Qi, Zhengji Zhou, Dongxing Kou, Wenhui Zhou, Shengjie Yuan, Sixin Wu (2024). Revealing the Role of Hydrogen in Highly Efficient Ag-Substituted CZTSSe Photovoltaic Devices: Photoelectric Properties Modulation and Defect Passivation. Nano-Micro Letters. https://doi.org/10.1007/s40820-024-01574-3
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Frequently Asked Questions
What is the main challenge in CZTSSe solar cells?
The presence of SnZn-related defects causes large irreversible energy loss and non-radiative recombination, limiting efficiency.
How does Ag substitution affect CZTSSe devices?
Ag substitution suppresses SnZn defects but leads to poor electrical conductivity and low carrier density.
What is the role of hydrogen in the Ag-substituted CZTSSe?
Hydrogen incorporation improves electrical conductivity and carrier density, and forms functional groups that passivate defects.
What efficiency was achieved in this study?
A champion efficiency of 14.74% was achieved using Ag/H co-doping.
What is the significance of this work?
It provides a promising strategy for high-efficiency kesterite-based solar cells by combining defect passivation and photoelectric property modulation.
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