Key Takeaways & Executive Findings
- •• Integrating perovskite solar cells onto irregular rough CuIn(Ga)Se2 (CIGS) surfaces remains a challenge; new strategy was explored to develop monolithic perovskite/CIGS tandem solar cell by manipulating the crystallization of perovskite. • Surface reconstruction and field-effect passivation are developed synergistically to issue complex interface relationship between perovskite and C60. • The champion power conversion efficiency (PCE) of 24.6% realized, providing significant commercial opportunities for all thin-film-based perovskite/CIGS tandem cells. • D-homoserine lactone hydrochloride improves coverage and passivates bulk defects by modulating PVK crystal growth, while 2-TEAI/DMF and LiF reduce interface recombination.
Abstract
Two-terminal (2-T) perovskite (PVK)/CuIn(Ga)Se2 (CIGS) tandem solar cells (TSCs) have been considered as an ideal tandem cell because of their best bandgap matching regarding to Shockley–Queisser (S–Q) limits. However, the nature of the irregular rough morphology of commercial CIGS prevents people from improving tandem device performances. In this paper, D-homoserine lactone hydrochloride is proven to improve coverage of PVK materials on irregular rough CIGS surfaces and also passivate bulk defects by modulating the growth of PVK crystals. In addition, the minority carriers near the PVK/C60 interface and the incompletely passivated trap states caused interface recombination. A surface reconstruction with 2-thiopheneethylammonium iodide and N,N-dimethylformamide assisted passivates the defect sites located at the surface and grain boundaries. Meanwhile, LiF is used to create this field effect, repelling hole carriers away from the PVK and C60 interface and thus reducing recombination. As a result, a 2-T PVK/CIGS tandem yielded a power conversion efficiency of 24.6% (0.16 cm2), one of the highest results for 2-T PVK/CIGS TSCs to our knowledge. This validation underscores the potential of our methodology in achieving superior performance in PVK/CIGS tandem solar cells.
1. Introduction
Two-terminal (2-T) perovskite (PVK)/CuIn(Ga)Se2 (CIGS) tandem solar cells (TSCs) have been considered as one of the most promising tandem technologies because of their bandgap matching capacity, regarding to Shockley–Queisser (S-Q) limit [1–3]. However, this tandem technology has been suffering from low performances in past years [4–8].
An obstacle of fabricating high-performance PVK/CIGS TSCs is the nature of the irregular rough surface morphology of commercial CIGS, which is typical lateral feature sizes in the order of 500 nm to 1 μm randomly distributing on CIGS surface [2, 7]. Consequently, incomplete surface coverage and shunt paths can easily take place while fabricating tandem devices [2, 9]. A chemical mechanical polishing interconnection layer strategy was used by Han et al. to smoothen surfaces, while Jošt et al. chose a highly technological co-evaporation method to prepare a uniform active CIGS surface [10, 11]. However, no whether polishing the interconnection layer or modifying CIGS preparing technology to obtain a smooth surface is costly and incompatible with industry. It is necessary to manipulate the deposition of top-cells. Normally, the growth orientation of the PVK crystals on the substrate is not under control, particularly in the case of more complex rough surfaces, resulting in disordered growth of grain. Strategies can be explored to manipulate the crystallization of PVK, to achieve the preferred orientation of grain growth to fully cover irregular (nano) rough surfaces [12–16]. In addition, incomplete passivation of trap states in PVK films and minority carriers near the interface is prone to trigger interface recombination, in turn reducing the efficiency of the device [17–22]. Growing the non-uniform PVK absorbers on the rough surface of CIGS resulted in more defects, which require further enhanced quality and mitigated recombination losses [23–26].
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Cong Geng, Kuanxiang Zhang, Changhua Wang, Chung Hsien Wu, Jiwen Jiang, Fei Long, Liyuan Han, Qifeng Han, Yi-Bing Cheng, Yong Peng (2024). Crystallization Modulation and Holistic Passivation Enables Efficient Two-Terminal Perovskite/CuIn(Ga)Se2 Tandem Solar Cells. Nano-Micro Letters. https://doi.org/10.1007/s40820-024-01514-1
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Frequently Asked Questions
What is the main challenge in fabricating perovskite/CIGS tandem solar cells?
The main challenge is the irregular rough surface morphology of commercial CIGS, which leads to incomplete coverage and shunt paths, reducing device performance.
How does D-homoserine lactone hydrochloride improve the perovskite layer?
D-homoserine lactone hydrochloride modulates the crystallization of perovskite, improving coverage on rough CIGS surfaces and passivating bulk defects.
What is the role of 2-thiopheneethylammonium iodide (2-TEAI) and DMF in the device?
2-TEAI and DMF assist in surface reconstruction and passivation of defect sites at the perovskite surface and grain boundaries, reducing interface recombination.
What is the significance of the achieved power conversion efficiency?
The champion device achieved a power conversion efficiency of 24.6%, which is one of the highest results for two-terminal perovskite/CIGS tandem solar cells, demonstrating commercial potential.
How does LiF contribute to the device performance?
LiF creates a field effect that repels hole carriers away from the perovskite/C60 interface, reducing recombination and improving efficiency.
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