Emerging technologies in solar energy will be critical in enabling worldwide society in overcoming the present energy challenges and reaching carbon net zero. Inefficient and unstable charge transport materials limit the current emerging energy conversion and storage technologies. Low-dimensional coordination polymers represent an alternative, unprecedented class of charge transport materials, comprised of molecular building blocks. Here, we provide a comprehensive study of mixed-valence coordination polymers from an analysis of the charge transport mechanism to their implementation as hole-conducting layers. CuII dithiocarbamate complexes afford morphology control of 1D polymer chains linked by (CuI2X2) copper halide rhombi. Concerted theoretical and experimental efforts identified the charge transport mechanism in the transition to band-like transport with a modeled effective hole mass of 6me. The iodide-bridged coordination polymer showed an excellent conductivity of 1 mS cm−1 and a hole mobility of 5.8 10−4 cm2 (V s)−1 at room temperature. Nanosecond selective hole injection into coordination polymer thin films was captured by nanosecond photoluminescence of halide perovskite films. Coordination polymers constitute a sustainable, tunable alternative to the current standard of heavily doped organic hole conductors.
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In 2017, the group of Prof. Dr Wilfried Wurth (University of Hamburg/DESY) and Dr Giuseppe Mercurio helped characterize thin films of our coordination polymers with X-ray photoelectron spectroscopy. Prof. Wurth passed away unexpectedly in May 2019 at the age of 62 and our heartfelt condolence shall be expressed to those around him. We appreciate experimental assistance from Aneta Andruszkiewicz, Zackary Ashworth, Olle Gustafsson (Uppsala) and Dr Jamie Gould (Newcastle) and owe gratitude to Dr Pablo Docampo (Glasgow/Newcastle) for discussions and access to his laboratory. Our appreciation goes out to Prof. Andrew Houlton for helpful suggestions and discussion. M. F. acknowledges the support by the Royal Society University Research Fellowship (URF\R1\191286), Research Grant 2021 (RGS\R1\211321), Göran Gustafsson Young Researcher Prize and EPSRC New Investigator Award (EP/V035819/1). H. M. acknowledges support from the European KIT InnoEnergy PhD program. M. J. G. is funded by the Royal Society of Chemistry. A. W. is supported by a Royal Society University Research Fellowship. Via the membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service. We are grateful to the UK Materials and Molecular Modelling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1). This research was supported by the Swedish Energy Agency (42037-1 and 43294-1), the STandUP for Energy program, and the National Research Foundation of Korea (NRF-2020R1A6A3A03039130). The authors thank the Diamond Light Source for access to beamline I19 in remote-access mode (beam-time award CY22240).
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