Charge modulation spectroscopy of solution-processable field-effect transistors

Abstract

Recent development of cost-effective, flexible, and large area optoelectronic devices has increased demand for high-performance, solution-processable field-effect transistors (FETs) to drive active devices and circuits. Among the materials of choice to realize solution-processable FETs are organic conjugated polymers and hybrid organic-inorganic perovskite semiconductors, gifted by high charge carrier mobilities and compositionally tunable optoelectronic properties. Given the complexity of such systems compared to conventional inorganic semiconductors, the implementation and optimization of polymer and perovskite FETs requires deep understanding of their charge transport properties as well as their device physics. In this thesis work, we studied prototypical solution-processable semiconducting materials for unipolar, ambipolar, and light-emitting FETs. We employed charge modulation spectroscopy (CMS), a unique electrical pump-optical probe technique that allows selective unipolar excitation and in situ probing of charge transport characteristics of operating devices, with spatial resolution down to optical diffraction limit. By analyzing charge-induced absorption and vibrational features of polymer FETs, we were able to determine local charge carrier concentrations and distributions, and elucidate their relationship with structural characteristics of the active layers. Moreover, using an ambipolar hybrid organic-inorganic perovskite as active material, we realized the first perovskite light-emitting FET. Our results lay down the path for developing mathematical device models as well as optimizing the molecular design of organic and hybrid organic-inorganic semiconductors for the development of high-performance, solution-processable FETs, as well as high brightness light-emitting devices like gated light-emitting diodes and electrical injection lasers.