Tuning self-assembled monolayers of Me-4PACz with bisphosphonic acid groups to improve temperature and cycling stability of perovskite photovoltaics

Haonan Sun^a^,^b, Guibin Shen^c, Huei Min Chua^c, Darrell Jun Jie Tay^d, Yuanjie Su^e^,^f, Yahong Pu^e^,^f, Yanju Wang^c, Yeow Boon Tay^d, Hongkang Fu^a, Subodh G. Mhaisalkar^b^,^d, Shixuan Du^e^,^f, Nripan Mathews^b^,^d, Wei Lin Leong^b^,^c

^aInterdisciplinary Graduate Programme (IGP), Graduate College, Nanyang Technological University, Singapore, 637460 Singapore

^bEnergy Research Institute @ NTU (ERI@N), Nanyang Technological University, Singapore, 637553 Singapore

^cSchool of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 Singapore

^dSchool of Materials Science and Engineering, Nanyang Technological University, Singapore, 639798 Singapore

^eBeijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China

^fSchool of Physics, University of Chinese Academy of Sciences, Beijing, 100049 China

Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV26)

Uppsala, Sweden, 2026 May 18th - 20th

Organizers: Gerrit Boschloo, Ellen Moons, Feng Gao and Anders Hagfeldt

Poster, Haonan Sun, 139
Publication date: 11th March 2026

Buried interface quality in p-i-n perovskite solar cells (PSCs) is shown to improve via the use of a mixed self-assembled monolayer (SAM) of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me‐4PACz) and (9H,9'H-[3,3'-bicarbazole]-9,9'-diylbis(butane-4,1-diyl))diphosphonic acid (Bi4PACz), eschewing the need for a NiOx layer. The bisphosphonic acid-based Bi4PACz minimizes SAM aggregation and enhances wettability and uniformity. It also coordinates with the perovskite, passivating defects and suppressing PbI₂ aggregation, thereby minimizing recombination losses. The improved buried interface quality leads to power conversion efficiencies (PCEs) of 24.48%, 25.65%, and 22.60% for triple cation PSCs with bandgaps of 1.61, 1.58, and 1.68 eV, respectively, demonstrating the wide applicability of this approach. Under temperature conditions, the PSCs retained 84% of initial PCE after 1200 h at 85 °C, and 97% after 250 thermal cycles (-40 °C to +70 °C), indicating its potential for space-related applications. This mixed-SAM approach establishes a universal pathway toward efficient and temperature-stable perovskite photovoltaics.

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