pH Modulation for Self-Assembly-Monolayer Type Hole Transport Layer for Efficient and Stable Perovskite-Silicon Double-Junction Solar Cells

Runmin Tao^a^,^b, Guoliang Wang^a^,^b, Zhihao Li^c, Nan Sun^d, Jueming Bing^a^,^b, Tik Lun Leung^a^,^b, Fraser J. Angus^e, Jianbo Tang^f^,^g, Chwenhaw Liao^a^,^b, Jianpeng Yi^a^,^b, Christopher Bailey^a^,^b, Li Liu^h, Yu Wangⁱ, Gaosheng Huang^d, Andreas Lambertz^d, Songyan Yin^j, Bin Gong^j, Alex-Anthony Cavallaro^k, Drew Evans^k, Matthew Griffith^k, Kourosh Kalantar-Zadeh^f^,^h, Jianghui Zheng^a^,^b, Pablo Docampo^e, David R. McKenzie^a^,^b, Md Arafat Mahmud^a^,^b, Kaining Ding^d, Annita W.Y. Ho Baillie^a^,^b

^aSchool of Physics, The University of Sydney, Sydney, NSW 2006, Australia

^bSydney Nano, The University of Sydney, Sydney, NSW 2006, Australia

^cSchool of Nanoscience and Materials Engineering, Henan University, Kaifeng, 475004 P. R. China

^dMD-3 Photovoltaics, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany

^eDepartment of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, U.K.

^fSchool of Chemical Engineering, University of New South Wales (UNSW), Kensington, Sydney, NSW 2052, Australia

^gSchool of Engineering and Research Centre for Industries of the Future, Westlake University, Hangzhou 310030, China

^hFaculty of Engineering, School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW 2006, Australia

ⁱX-ray Diffraction Lab, SSEAU, Mark Wainwright Analytical Centre, University of New South Wales (UNSW), Kensington, Sydney, NSW 2052, Australia

^jSurface Analysis Laboratory, Mark Wainwright Analytical Centre, University of New South Wales (UNSW), Kensington, Sydney, NSW 2052, Australia

^kFuture Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia

^lAustralian Centre for Advanced Photovoltaics (ACAP), University of New South Wales, Sydney, NSW, 2052 Australia

Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP26)

Nagoya, Japan, 2026 January 13th - 15th

Organizers: Pablo P. Boix and Seigo Ito

Oral, Runmin Tao, presentation 086
Publication date: 5th November 2025

Self-assembled monolayer (SAM) hole transport layer are commonly used in state-of-the-art perovskite single- and multi-junction solar cells. Their precursor molecules are prone to aggregation. We report SAM-solution-pH-modulation that effectively suppresses aggregation, improving deposited film quality. We designed and synthesized a novel material, 6-aminohexylphosphonic acid hydrochloride (6AHPACl), to be added to the (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid) Me-4PACz solution as part of a co-SAM strategy. Apart from the advantage of pH-modulation, the inclusion of 6AHPACl improved SAM anchoring; SAM/perovskite interface energetics; wettability of the overlaying perovskite layer and therefore its quality. This co-SAM strategy enabled demonstrations of a wide-bandgap (1.67 eV) perovskite cell producing a champion efficiency of 22.8%, and a 1cm² monolithic perovskite-silicon double junction (2J) cell producing a certified efficiency of 29.1%. An encapsulated device retained 95% of its efficiency after 1010 Thermal Cycles (-40℃ to 85℃). Another encapsulated 2J device surpassed the International Electrotechnical Commission (IEC) 61215 Humidity Freeze test.

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