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Organic mixed ionic and electronic conductors (OMIECs) are an emerging class of materials that have been applied for a wide range of electrochemical applications. Due to the complexity inherent to the ionic-electroniccoupling, understanding the underlying mechanisms involved in the OMIEC operation is an exciting and very lively research field. In this work, we highlight the use of time-resolved Vis-NIR spectroelectrochemistry tocharacterize these materials. We discuss an example, where we show that by combining this tool with spectraldecomposition, we are able to understand fundamental aspects of the doping in an OMIEC film. The methodswe present here can be generalized and used to characterize any electrochromic material.

The power conversion efficiency of organic solar cells has seen a huge improvement in recent years with state-of-the-art solar cells showcasing efficiencies of ∼18.5 %, which is approaching the performance of inorganic and hybrid-perovskite solar cell technologies. This improvement can be mainly attributed to the discovery of highly efficient donor:acceptor blends with a near-zero energetic offset between the molecular orbital levels of the donor and the acceptor component. A distinctive feature of the high efficiency, low energy-offset blends is that they exhibit a concomitant increase in the short-circuit density and the open-circuit voltage of the solar cell. High open-circuit voltage results from the reduced photon energy loss in the exciton dissociation step, while a high short-circuit current density can be attributed to an efficient charge generation process. The reasons for the efficient exciton dissociation and subsequent separation of Coulomb bound electron-hole pair at negligible driving force is not well understood and, in this short review, we highlight recent results which shed light on the mechanism of charge generation in low energy-offset blends.

Understanding the electrochemical doping of organic semiconductors plays a crucial role in the current development of organic electronics. In this short review, we present how temperature- and time- dependent visible-near-infrared (Vis-NIR) spectro-electrochemistry and terahertz spectroscopy, combined with multivariate curve resolution analysis, can inform on the fundamental mechanisms governing the doping kinetics and efficiency of two archetypal semiconducting polymers (PEDOT and P3HT). We highlight the experimental procedures and data analysis performed to access (i) the thermodynamic parameters driving the extent and dynamics of electrochemical reactions in doped systems and (ii) how the density and nature of charged species (polarons, bipolarons) impact the charge carrier delocalization, effective THz mobility and hence short-range conductivity.

Organic solar cells consist of thin films combining an electron donor (often a conjugated polymer) with an electron acceptor (often a fullerene derivative), in a blend commonly referred to as bulk heterojunction material. Charge separation between the donor and the acceptor leads to the generation of carriers, which can be extracted from photovoltaic devices in the form of photocurrent. The generation mechanism of free, extractable charges has caused a lot of controversial discussion in literature. Our research has shown that all the steps involved in charge generation are strongly dependent on the arrangement of the donor and the acceptor (i.e. the structure) of the bulk heterojunction.

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a RuII(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the ?s time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor ? = 0.16 Å?1 observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface.