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Breaking the reaction chain - Nature Energy
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Wide band gap perovskite solar cells suffer from halide segregation, which hampers their use in tandem solar cells. Now, researchers develop an additive with redox and defect passivating capabilities to suppress halide migration, enabling perovskite–organic tandems with over 25% efficiency.
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Metal halide perovskite materials are of significant interest for application in tandem solar cells since their band gap can be easily tuned using mixed-halide perovskites by optimizing the iodide to bromide ratio to complement the band gap of the other sub-cell in the tandem device. In particular, wide band gap (WBG) perovskites can be used in combination with narrow band gap organic solar cells in perovskite–organic tandems. Yet, due to the high Br content of WBG perovskites, these solar cells commonly exhibit halide segregation under illumination or bias. This phenomenon is initiated by photoinduced oxidation of iodide which then drives halide migration 1 , 2 , adversely affecting the device performance and eventually leading to performance degradation. Thus, the suppression of halide segregation is imperative to improve performance of WBG perovskite solar cells and consequently achieve high-efficiency, high-stability tandem solar cells.
Writing in Nature Energy , Alex K.-Y. Jen and colleagues at City University of Hong Kong and The Hong Kong Polytechnic University report anthraquinone-based redox mediators with ammonium counter-cations for simultaneous reversal of detrimental redox reactions in WBG perovskites and passivation of defects 3 . The researchers demonstrate a high open circuit voltage of 1.35 V in WBG perovskite solar cells, resulting in an improved efficiency of perovskite–organic tandem solar cells, which reaches 25.22% (certified efficiency of 24.27%).
The role of redox reactions in halide redistribution under bias or illumination has been gaining recognition in recent years 1 , 2 . The use of redox shuttles can mitigate halide segregation through cyclical defect recovery by oxidizing reduced lead and reducing oxidized iodide, as illustrated in Fig. 1 . However, the use of redox additives in perovskite solar cells has been scarce 4 , 5 . Similar to previously reported rare-earth based Eu 2+ /Eu 3+ 4 and Fc/Fc + ferrocene redox shuttles 5 , the 2-sulfonate anthraquinone core of the redox mediator proposed by Jen and team oxidizes reduced lead and reduces oxidized iodide. Yet, the researchers take it further and add a defect passivating capability by introducing ammonium or phenylethylammonium groups as counter-cations. As a result, Jen and team are able to not only suppress photoinduced halide segregation by reducing iodide oxidation, but also enhance the open circuit voltage by passivating defects and reducing nonradiative recombination.
Fig. 1: Redox processes in perovskite film under illumination and the effect of the anthraquinone redox additive. a , Upon illumination, holes and electrons are generated in the perovskite layer. The photogenerated holes and electrons interact with iodide anions and lead cations in the perovskite lattice, respectively. The reaction between the hole and iodide leads to the formation of neutral iodine interstitial defects (I i 0 ), iodine (I 2 ), and iodide vacancies (vacancy type defects are denoted as V X , where X is the missing ion). The reaction between the electrons and Pb 2+ leads to the formation of metallic lead (Pb 0 ). The description of the process is based on refs. 1 , 2 , 3 , 9 . The phenethylammonium group (PEA + ) passivates defects at the perovskite surface. b , The 2-sulfonate anthraquinone redox anion (AQS – ) reverts these reactions by oxidizing reduced lead and reducing oxidized iodide. Panel b is adapted with permission from ref. 3 , Springer Nature Ltd.
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The researchers investigate the impact of the defect passivating function by comparing anthraquinone-based redox mediators with different counter-cations. In the case of H + , they obtain only small improvement in charge carrier lifetime and device performance, despite significant suppression of halide segregation. In fact, H + has limited defect passivation ability. In contrast, they show that redox mediators containing ammonium or phenethylammonium species result in a more significant suppression of nonradiative recombination and larger increase in open circuit voltage, with the best performance obtained with the phenethylammonium counter-cation.
Consequently, the researchers achieve an efficiency of 19.58% and a 500-h operational stability for WBG perovskite solar cells using a 2-sulfonate anthraquinone redox anion combined with the phenethylammonium cation, outperforming the control device without redox mediator additive. When integrated in a perovskite–organic tandem solar cell, the efficiency reaches 25.22% with an operational stability over 500 h. This efficiency is higher than previous reports, which primarily focused on optimizing the interconnecting layer and minimizing the defects/nonradiative recombination losses in WBG perovskite cell and achieved ~23% efficiency 6 , 7 , 8 .
The work of Jen and team illustrates the importance of simultaneously tackling detrimental redox reactions and defects in perovskite solar cells. As discussed above, redox shuttles mitigate halide segregation by reversing defect-creating redox reactions but could not tackle other defects. On the other hand, the simple passivation of defects is insufficient to ensure high efficiency and stable operation under illumination due to the fact that iodide is readily oxidized under illumination or bias 2 , 9 . This means that even if the defects in the bulk and at the interfaces of the perovskite have been initially passivated, new defects are constantly created during device operation due to redox reactions, which lead to ion migration and ultimately device performance degradation. Therefore, there is still work to be done to optimize this approach.
Oxidation of iodide during operation occurs not only in solar cells based on WBG perovskites but also perovskites with other compositions. In future work, the combined use of redox mediators and defect passivation can be explored to improve the device stability of these other perovskite solar cells. In tandem cells, instead, the redox and passivation approach developed by Jen and team could perhaps be combined with the optimization of the interconnect layer, perovskite/charge transport layer interfaces, or organic sub-cell to further improve the performance of the devices.
References .
Yu, X., Wang, Y. & Gao, P. ChemPhotoChem 7 , e202200311 (2023).
Article ? Google Scholar ?
Xu, Z. et al. ACS Energy Lett. 8 , 513–520 (2023).
Article ? Google Scholar ?
Wu, S. et al. Nat. Energy https://doi.org/10.1038/s41560-024-01451-8 (2024).
Article ? Google Scholar ?
Wang, L. et al. Science 363 , 265–270 (2019).
Article ? Google Scholar ?
Chang, Q. et al. Angew. Chem. Int. Ed. 60 , 25567–25574 (2021).
Article ? Google Scholar ?
Brinkmann, K. O. et al. Nature 604 , 280–286 (2022).
Article ? Google Scholar ?
Chen, W. et al. Nat. Energy 7 , 229–237 (2022).
Article ? Google Scholar ?
Yang, H. et al. Adv. Mater. 35 , 2208604 (2023).
Article ? Google Scholar ?
Xu, Z., Kerner, R. A., Berry, J. J. & Rand, B. P. Adv. Funct. Mater. 32 , 2203432 (2023).
Article ? Google Scholar ?
Download references
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Department of Physics, The University of Hong Kong, Hong Kong SAR, China
Aleksandra B. Djuri?i?
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Djuri?i?, A.B. Breaking the reaction chain. Nat Energy (2024). https://doi.org/10.1038/s41560-024-01503-z
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Published : 28 March 2024
DOI : https://doi.org/10.1038/s41560-024-01503-z
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