Effects of Additives on Crystallization and Device Performance in CsPbI2Br Perovskite Solar Cells

HANBO JUNG^a^,^b, PANGPANG WANG^c, SUNAO YAMADA^c, Kaoru Tamada^d, Yue Hu^e, Shuhei Matsumura^f, Ayumi Ishii^f, Toshinori Matsushima^a^,^b^,^g, Zhanglin Guo^a^,^b^,^g

^aWPI-I2CNER, Kyushu University

^bCenter for Energy Systems Design (CESD), International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Japan

^cMaterials Open Lab., Institute of Systems, Information Technologies and Nanotechnologies (ISIT),

^dInstitute for Materials Chemistry and Engineering, Kyushu University

^eSchool of Chemistry, University of Edinburgh, Edinburgh

^fDepartment of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University

^gDepartment of Automotive Science, Graduate School of Integrated Frontier Sciences, Kyushu University

Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP27)

Fukuoka, Japan, 2027 January 18th - 20th

Organizers: Zhanglin Guo and Tingli Ma

Poster, HANBO JUNG, 111
Publication date: 22nd October 2026

All-inorganic CsPbI₂Br has a bandgap of approximately 1.92 eV, making it a promising absorber for the top subcell of tandem solar cells.[1] However, inverted (p–i–n) CsPbI₂Br devices exhibit substantial open-circuit voltage V_OC losses associated with halide inhomogeneity and nonradiative recombination.[2] Here, we show that adding 1 mol% PbCl₂ to a CsBr/PbI₂ precursor solution alters crystallization during both room-temperature resting and thermal annealing, yielding films with a more uniform halide distribution across their thickness.

To investigate the role of precursor–solvent coordination in crystallization,[3] we combined infrared and ¹³C NMR spectroscopy with quasi-in situ X-ray diffraction. Changes in the carbonyl and sulfoxide vibrational bands, together with shifts in the ¹³C NMR resonances, indicated that PbCl₂ modifies precursor interactions with DMF and DMSO. The integrated intensity of the perovskite (100) reflection began to rise earlier during room-temperature resting and increased more gradually during annealing, consistent with an earlier onset of crystallization followed by more gradual crystal growth.

Time-of-flight secondary ion mass spectrometry revealed pronounced depth-dependent variations in the iodide and bromide signals of the control films. Adding PbCl₂ yielded more uniform halide profiles, which can limit local bandgap fluctuations.[4] The modified films also exhibited smaller surface potential variations and greater resistance to light-induced halide segregation. The absolute photoluminescence quantum yield of the ITO/NiO_x/SAM/perovskite stack increased from 0.155% to 0.510%, corresponding to a reduction of approximately 31 mV in the nonradiative voltage loss.

The champion device containing 1 mol% PbCl₂ achieved a power conversion efficiency (PCE) of 16.34% and a V_OC of 1.25 V, compared with 12.40% and 1.16 V for the control. Under continuous illumination at 25 °C, encapsulated PbCl₂-modified devices retained 73% of their initial PCE after 500 h of maximum power point operation. These results link crystallization control during film formation to improved halide homogeneity, reduced voltage loss, and enhanced operational stability in inverted CsPbI₂Br solar cells.

References:

[1] l-Ashouri, A.; Köhnen, E.; Li, B.; Magomedov, A.; Hempel, H.; Caprioglio, P.; Márquez, J. A.; Morales Vilches, A. B.; Kasparavicius, E.; Smith, J. A.; Phung, N.; Menzel, D.; Grischek, M.; Kegelmann, L.; Skroblin, D.; Gollwitzer, C.; Malinauskas, T.; Jošt, M.; Matič, G.; Rech, B.; Schlatmann, R.; Topič, M.; Korte, L.; Abate, A.; Stannowski, B.; Neher, D.; Stolterfoht, M.; Unold, T.; Getautis, V.; Albrecht, S. Monolithic Perovskite/Silicon Tandem Solar Cell with >29% Efficiency by Enhanced Hole Extraction. Science 2020, 370, 1300–1309.

[2] Warby, J.; Zu, F.; Zeiske, S.; Gutierrez-Partida, E.; Frohloff, L.; Kahmann, S.; Frohna, K.; Mosconi, E.; Radicchi, E.; Lang, F.; Shah, S.; Peña-Camargo, F.; Hempel, H.; Unold, T.; Koch, N.; Armin, A.; De Angelis, F.; Stranks, S. D.; Neher, D.; Stolterfoht, M. Understanding Performance Limiting Interfacial Recombination in pin Perovskite Solar Cells. Adv. Energy Mater. 2022, 12, 2103567

[3] Wang, K.; Sun, W.; Liu, W.; Huo, X.; Yin, R.; Liu, J.; Gao, Y.; You, T.; Yin, P. Mitigating Interfacial and Bulk Defects via Chlorine Modulation for HTL-Free All-Inorganic CsPbI₂Br Carbon-Based Perovskite Solar Cells with Efficiency over 14%. Chem. Eng. J. 2022, 445, 136781

[4] Frohna, K.; Chosy, C.; Al-Ashouri, A.; Scheler, F.; Chiang, Y.-H.; Dubajic, M.; Parker, J. E.; Walker, J. M.; Zimmermann, L.; Selby, T. A.; Lu, Y.; Roose, B.; Albrecht, S.; Anaya, M.; Stranks, S. D. The Impact of Interfacial Quality and Nanoscale Performance Disorder on the Stability of Alloyed Perovskite Solar Cells. Nat. Energy 2025, 10, 66–76.

Acknowledgements:

This work was supported by the Iwatani Naoji Foundation; Royal Society International Science Partnerships Fund-International Collaboration Award 2025; JSPS KAKENHI (grant number 26K17944, 24H00486); Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST) (grant number JPMJPR23H8); New Energy and Industrial Technology Development Organization (NEDO), the Green Innovation Fund Project (grant number 21578635); Science and Technology Research Partnership for Sustainable Development (SATREPS), JST (grant number JPMJSA2306); ASPIRE FOR RISING SCIENTISTS, Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE) (grant number JPMJAP2332), JST; the Asahi Glass Foundation; Mitsui Chemicals, Inc.—Carbon Neutral Research Center (MCI-CNRC), International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University; and Kuma Foundation for the Promotion of Science, Technology and Culture. We acknowledge the donation of a research facility from KOREA KIYON Co., Ltd.

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