Hybrid Organic-Inorganic Coordination Complexes as Tunable Optical Response Materials.

Will Travis,Hugo Bronstein,Jeremy K Cockcroft,Alex M Ganose,Panagiota Kafourou,David O Scanlon,Christopher N Savory,Zainab Sharif,Xingchi Song,Robert G Palgrave,Caroline E Knapp

doi:10.1021/acs.inorgchem.5b02749

Will Travis, Hugo Bronstein + Show 9 more

Open Access

https://doi.org/10.1021/acs.inorgchem.5b02749

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Abstract

Novel lead and bismuth dipyrido complexes have been synthesized and characterized by single-crystal X-ray diffraction, which shows their structures to be directed by highly oriented π-stacking of planar fully conjugated organic ligands. Optical band gaps are influenced by the identity of both the organic and inorganic component. Density functional theory calculations show optical excitation leads to exciton separation between inorganic and organic components. Using UV-vis, photoluminescence, and X-ray photoemission spectroscopies, we have determined the materials' frontier energy levels and show their suitability for photovoltaic device fabrication by use of electron- and hole-transport materials such as TiO2 and spiro-OMeTAD respectively. Such organic/inorganic hybrid materials promise greater electronic tunability than the inflexible methylammonium lead iodide structure through variation of both the metal and organic components.

Highlights

Solar energy is regarded as perhaps the most promising alternative to fossil fuels.[1]
MAPI is unstable in moist air and rapidly degrades when held at operating temperatures, forming methylammonium iodide and PbI2.12
Four post-transition metal iodide dipyrido coordination complexes have been synthesized and structurally characterized. These materials demonstrate promising tunability of their optical, structural, and electronic properties and show promise for potential applications as PV absorbers. They represent a possible alternative to the perovskite structure, which offers very little compositional flexibility

Summary

Introduction

Solar energy is regarded as perhaps the most promising alternative to fossil fuels.[1] In recent years, solar cells based on hybrid organic−inorganic absorbers with perovskite structure have shown potential as an alternative to silicon solar cells.[2] Perovskite solar cells already show efficiencies surpassing those of dye-sensitized, organic, and amorphous silicon solar modules.[3] The archetypal perovskite solar cell absorber material is methylammonium lead(II) iodide (CH3NH3PbI3 or MAPI) and has significant advantages over competing commercial and emerging technologies: synthesis is achieved from available and cheap starting materials via solution processes[4] or scalable vapor-phase deposition methods,[5] making possible large-scale industrial production.[6] efficiencies of MAPI solar cells have exceeded 20%.4b,7 Such high efficiencies have been achievable due to MAPI’s high optical absorption coefficient, excellent defect tolerance,[8] ambipolar charge transport,[9] and very long electron−hole diffusion lengths[10] which result from high minority-carrier lifetime (τ) and mobility (μ).10b,11 An important factor in each of these properties is thought to be the three-dimensional (3D) connectivity of the inorganic (lead iodide) sublattice in the perovskite structure. MAPI is unstable in moist air and rapidly degrades when held at operating temperatures, forming methylammonium iodide and PbI2.12

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