Physics:Tin-based perovskite solar cell

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A tin-based perovskite solar cell is a special type of perovskite solar cell, where the lead is substituted by tin. It has a tin-based perovskite structure (ASnX3), where 'A' is a 1+ cation and 'X' is a monovalent halogen anion. The methylammonium tin triiodide (CH3NH3SnI3) has a band gap of 1.2–1.3 eV, while formamidinium tin triiodide has a band gap of 1.4 eV. Tin-based perovskite solar cells are still in the research phase and there are relatively few publications about them, compared to their counterpart, lead-based perovskite solar cells. This is mainly due to the instability of the 2+ oxidation state of tin (Sn2+) in methylammonium tin iodide (CH3NH3SnI3), which can be easily oxidized to the more stable Sn4+,[1] leading to a process called self doping,[2] where the Sn4+ acts as a p-dopant leading to a reduction in the solar cell efficiency. Self-doping used to be believed to be caused by Sn vacancy defects; however, recent research indicates that this may not be complete.[3] In CsSnI3, Cs vacancies are the primary contributors of holes leading to self-doping.[3]

The maximum solar cell efficiency reported is 18.71% for methylammonium tin iodide (CH3NH3SnI3),[4] 5.73% for CH3NH3SnIBr2,[5] 3% for CsSnI3 (quantum dots of this material can yield efficiencies as high as 5.03%)[4]. and above 9% for formamidinium tin triiodide (CH(NH2)2SnI3).[6][7]

The main advantages of tin-based perovskite solar cells are that they are lead-free and that can help to further tune the band-gap of the active layer. There are environmental concerns with using lead-based perovskite solar cells in large-scale applications;[8][9] one such concern is that since the material is soluble in water, and lead is highly toxic, any contamination from damaged solar cells could cause major health and environmental problems.[10][11]

In spite of an earlier reported low efficiency, formamidinium tin triiodide may hold promise because, applied as a thin film, it appears to have the potential to exceed the Shockley–Queisser limit by allowing hot-electron capture, which could considerably raise the efficiency.[12]

Self Doping Mitigation techniques

Several techniques have been explored as a means of counteracting the self-doping of Sn-based perovskites. One method is the sealing of cells so that they are not exposed to oxygen.[13] Techniques that have been used to seal the cells include atomic layer deposition, roll lamination, using a heat sealer, and covering with glass sealed with adhesives cured by ultraviolet light.[13] Materials that have been used for this purpose include polymers such as poly(methyl methacrylate). [14]

Another option is adding reducing agents such as tin halides to the environment in which tin-based perovskite thin films are deposited to reduce perovskite oxidation.[13] They also act as a source of Sn, diminishing the likelihood of Sn vacancies (and, therefore, holes) forming; this improves the thin film structure.[13] Additional reducing agents include powdered Sn, gallic acid, and N2H4.[13] Adding certain organic compounds to precursor solutions can lead to the reduction of tin halides to metallic Sn, which can act as a sink for Sn(IV) ions formed during perovskite processing.[15]

A similar method is including a step in the perovskite film processing which removes Sn(IV) ions. This can be accomplished by coating the perovskite film with a material such as formamidinium hydrochloride (FACl) that forms a complex with Sn(IV) ions which can then be removed by heating to temperatures below 60C.[16] As long as the temperature to vaporize the complex is below that at which the perovskite loses mass, the perovskite film will remain intact after this processing step, save for the Sn(IV) ions which have been removed.[17] Another processing step which has been shown to reduce self-doping is annealing of perovskite films during deposition.[18]

A final possibility is improving the perovskite design itself to mitigate self-doping. One technique which can be used for this purpose in hybrid organic-inorganic perovskites is increasing the size of the organic component, which is believed to create a physical barrier to diffusion of oxygen.[19] Increasing the size of the organic cation of the perovskite (but not making it so large that a layered structure forms) has the additional benefit of decreasing the bulk Sn defect density, eliminating a site which impedes charge carrier motion and lowers efficiency.[20]


References

  1. ↑ Lee, S.J., et al., "Fabrication of Efficient Formamidinium Tin Iodide Perovskite Solar Cells through SnF2-Pyrazine Complex". Journal of the American Chemical Society, 2016.14.
  2. ↑ Takahashi, Y., et al., "Charge-transport in tin-iodide perovskite CH3NH3SnI3: origin of high conductivity". Dalton Transactions, 2011. 40(20): pp. 5563–p-5568.
  3. ↑ 3.0 3.1 Zhang, Jiajia, and Yu Zhong. “Origins of P‐Doping and Nonradiative Recombination in CsSnI 3.” Angewandte Chemie, vol. 134, no. 44, Nov. 2022. DOI.org (Crossref), https://doi.org/10.1002/ange.202212002.
  4. ↑ 4.0 4.1 Xu, Ke. Development of Tin-Based Perovskite Materials for Solar Cell Applications: ...: EBSCOhost. https://web-s-ebscohost-com.turing.library.northwestern.edu/ehost/pdfviewer/pdfviewer?vid=0&sid=09c3a302-4cac-4600-8961-89bfef27428b%40redis. Accessed 15 Oct. 2022.
  5. ↑ Hao, F., et al., "Lead-free solid-state organic-inorganic halide perovskite solar cells". Nature Photonics, 2014. 8(6): pp. 489–494.
  6. ↑ Shuyan Shao, Jian Liu, Giuseppe Portale, Hong‐Hua Fang, Graeme R. Blake, Gert H. ten Brink, L. Jan Anton Koster, Maria Antonietta Loi (2018). "Highly Reproducible Sn‐Based Hybrid Perovskite Solar Cells with 9% Efficiency". Advanced Energy Materials 8 (4): 1702019. doi:10.1002/aenm.201702019. 
  7. ↑ Efat Jokar, Cheng-Hsun Chien, Cheng-Min Tsai, Amir Fathi, and Eric Wei-Guang Diau, "Robust Tin-Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10%" Adv. Mat. 1804835 (2018)doi:10.1002/adma.201804835.
  8. ↑ Espinosa, N., et al., "Solution and vapour deposited lead perovskite solar cells: Ecotoxicity from a life cycle assessment perspective". Solar Energy Materials and Solar Cells, 2015. 137: pp. 303–310.
  9. ↑ Zhang, J., et al., "Life Cycle Assessment of Titania Perovskite Solar Cell Technology for Sustainable Design and Manufacturing". ChemSusChem, 2015. 8(22): pp. 3882–3891.
  10. ↑ Benmessaoud, I.R., et al., "Health hazards of methylammonium lead iodide based perovskites: cytotoxicity studies". Toxicology Research, 2016.
  11. ↑ Babayigit, A., et al., "Assessing the toxicity of Pb-and Sn-based perovskite solar cells in model organism Danio rerio". Scientific Reports, 2016. 6: p. 18721.
  12. ↑ Fang, Hong-Hua; Adjokatse, Sampson; Shao, Shuyan; Even, Jacky; Loi, Maria Antonietta (January 16, 2018). "Long-lived hot-carrier light emission and large blue shift in formamidinium tin triiodide perovskites". Nature Communications 9 (243): 243. doi:10.1038/s41467-017-02684-w. PMID 29339814. Bibcode: 2018NatCo...9..243F. 
  13. ↑ 13.0 13.1 13.2 13.3 13.4 Cao, Jiupeng, and Feng Yan. “Recent Progress in Tin-Based Perovskite Solar Cells.” Energy & Environmental Science, vol. 14, no. 3, 2021, pp. 1286–325, https://doi.org/10.1039/D0EE04007J.
  14. ↑ Yin, Yongqi, et al. “Stable and Efficient Tin-Based Perovskite Solar Cell via Semiconducting–Insulating Structure.” ACS Applied Energy Materials, vol. 3, no. 11, Nov. 2020, pp. 10447–52. DOI.org (Crossref), https://doi.org/10.1021/acsaem.0c01422.
  15. ↑ Hu, Shuaifeng, et al. “Mixed Lead–Tin Perovskite Films with >7 Μs Charge Carrier Lifetimes Realized by Maltol Post-Treatment.” Chemical Science, vol. 12, no. 40, 2021, pp. 13513–19, https://doi.org/10.1039/D1SC04221A.
  16. ↑ Zhou, Jianheng, et al. “Chemo-Thermal Surface Dedoping for High-Performance Tin Perovskite Solar Cells.” Matter, vol. 5, no. 2, Feb. 2022, pp. 683–93. DOI.org (Crossref), https://doi.org/10.1016/j.matt.2021.12.013.
  17. ↑ Zhou, Jianheng, et al. “Chemo-Thermal Surface Dedoping for High-Performance Tin Perovskite Solar Cells.” Matter, vol. 5, no. 2, Feb. 2022, pp. 683–93. DOI.org (Crossref), https://doi.org/10.1016/j.matt.2021.12.013.
  18. ↑ Mu, Haichuan, et al. “Effects of In-Situ Annealing on the Electroluminescence Performance of the Sn-Based Perovskite Light-Emitting Diodes Prepared by Thermal Evaporation.” Journal of Luminescence, vol. 226, Oct. 2020, p. 117493. ScienceDirect, https://doi.org/10.1016/j.jlumin.2020.117493.
  19. ↑ Lanzetta, Luis, et al. “Two-Dimensional Organic Tin Halide Perovskites with Tunable Visible Emission and Their Use in Light-Emitting Devices.” ACS Energy Letters, vol. 2, no. 7, July 2017, pp. 1662–68, https://doi.org/10.1021/acsenergylett.7b00414.
  20. ↑ Chang, Bohong, et al. “Efficient Bulk Defect Suppression Strategy in FASnI3 Perovskite for Photovoltaic Performance Enhancement.” Advanced Functional Materials, vol. 32, no. 12, Mar. 2022, p. 2107710. onlinelibrary-wiley-com.turing.library.northwestern.edu (Atypon), https://doi.org/10.1002/adfm.202107710.



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