Coordination complexes and polymers for Hybrid Photovoltaics Marina Freitag School of Natural and Enviromental Sciences, Newcastle University, UK Emerging energy conversion and storage technologies will be critical in resolving the current energy problem and achieving carbon net zero. They are currently constrained using inefficient, unstable, and expensive charge transport materials with limited tunability. And still, the development of novel charge transfer materials lags substantially behind attempts to produce light absorbing materials or other components in photovoltaics. 1 To develop efficient and sustainable hybrid solar cells, charge transport materials must meet the following criteria: I suitable energy levels adapted to the band gap of the absorbing material, ii) high conductivity, iii) simple processability, iv) chemical and thermal stability, and v) composition based on abundant elements, making coordination complexes and polymers (CCs and CPs) promising candidates. 2 Traditional redox mediators based on metal coordination complexes transport each electron through a change in the oxidation state of the metal centre. When preorganized ligands restrict coordination sphere reorganization, electron transfer kinetics are shifted toward favoured oxidation states. We recently developed a new dimeric copper (II/I) redox system in which the degree of oxidation/reduction of two metal centres governs the dynamic production of dimer and monomer complexes: the dimeric Cu(I) transitions to monomers of Cu (II). The unique two electron redox systems' bis(thiazole/pyrrole)-bipyridine tetradentate ligands stabilise both oxidation states. Through reduced recombination and quick charge transfer, dynamic dimer redox mediators provide a feasible two-electron redox mechanism for developing efficient hybrid solar cells. Inner reorganisation energies for single-electron transfer as low as 0.27 eV are shown by density functional theory calculations, making dimeric complexes preferable redox systems above single complexes as liquid and perhaps solid-state electrolytes. 4,5 In addition, we created low-dimensional, mixed-valence coordination polymers and the charge transport process and implemented them as hole conducting layers. CuII dithiocarbamate complexes influence the shape of 1D polymer chains connected by (CuI2X2) copper halide rhombi. The charge transport mechanism during the transition to band-like transport was established via collaborative theoretical and experimental efforts, with a predicted effective hole mass of 6 me. At ambient temperature, the iodide-bridged coordination polymer demonstrated high conductivity of 1 mS cm-1 and hole mobility of 5.8 10-4cm2Vs-1. Nanosecond photoluminescence of halide perovskite films recorded nanosecond selective hole injection into coordination polymer thin films. Coordination polymers are a long-term, tuneable alternative to the existing standard of extensively doped organic hole conductors. 3 References 1. Muñoz-García, A. B. et al. Chemical Society Reviews 50, 12450–12550 (2021)
2. Morritt, G. H. et al. Chemical Physics Reviews 3, 011306 (2022) 3. Michaels, H. et al. Journal of Materials Chemistry A (2022) 4. Freitag, M. et al. Nature Photonics 11, 372–378 (2017) 5. Benesperi, I. et al. Chem 8, 439–449 (2022)
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