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Lookup NU author(s): Dr Elisabetta Arca, Dr Pablo Docampo
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
This journal is © The Royal Society of Chemistry, 2025. Self-assembled molecules (SAMs) are widely used as hole-selective contacts in perovskite solar cells (PSCs). They are traditionally designed to facilitate charge injection by aligning their highest occupied molecular orbital (HOMO) with the perovskite's valence band. However, interfacial energy barriers may not necessarily hinder performance, and in some cases, can boost the devices' open-circuit voltage, thereby improving efficiency. This raises an important question: is injection through the SAM, to promote charge extraction, a necessary or even desirable criterion? To investigate this, we compare two Spiro-OMeTAD derivatives: Spiro-A, which is directly attached to the indium-doped tin oxide (ITO) anode by a carboxylic acid moiety, forcing the HOMO level to be in close proximity to the ITO, and Spiro-B, which incorporates a spacer group to separate the HOMO from ITO spatially. Contrary to expectations, Spiro-B achieves a higher open-circuit voltage (VOC) and power conversion efficiency (PCE) than Spiro-A despite having a lower built-in potential (VBI). Stabilise and pulse (SaP) measurements confirm that Spiro-B promotes charge accumulation by reducing interfacial recombination, thus increasing quasi-Fermi level splitting (QFLS). Furthermore, the carbazole-based reference SAM (Me-4PACz) achieves the highest VOC, demonstrating that direct charge injection is not always beneficial. These results challenge conventional molecular design strategies, emphasising the importance of controlling interfacial recombination over maximising charge injection. This work provides new insights for optimising SAMs in PSCs, offering a pathway toward higher efficiency through tailored energy barriers and charge accumulation dynamics.
Author(s): Angus FJ, Mackenzie L, Giza M, Wilkinson D, Arca E, Palomares E, Li W, Docampo P, Cooke G
Publication type: Article
Publication status: Published
Journal: Journal of Materials Chemistry A
Year: 2025
Volume: 13
Issue: 44
Pages: 38140-38148
Print publication date: 28/11/2025
Online publication date: 10/10/2025
Acceptance date: 01/10/2025
Date deposited: 07/01/2026
ISSN (print): 2050-7488
ISSN (electronic): 2050-7496
Publisher: Royal Society of Chemistry
URL: https://doi.org/10.1039/d5ta06749a
DOI: 10.1039/d5ta06749a
Data Access Statement: Data used to generate the main-text figures in this article are available at https://doi.org/10.5281/zenodo.15544593. Additional supporting data are provided in the supplementary information (SI). Supplementary information: complete synthetic procedure for Spiro-B. Additional characterisation of Spiro-B. Note on TRPL analysis. XPS spectra of all materials used and a table of associated data. Complete device parameters obtained from J–V characterisation. Stabilise and pulse measurement, VFlat analysis and stabilisation data from SaP measurement for all devices. See DOI: https://doi.org/10.1039/d5ta06749a
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