Publication Date

April 2019

Advisor(s)

Meng-ju Sher

Major

Chemistry

Language

English (United States)

Abstract

Hybrid organic-inorganic perovskites (HOIPs) are a class of semiconducting thin films, viable for solar cell applications, that have emerged as serious contenders to traditional silicon-based photovoltaic devices. Research over the past decade has shown that incorporating small amounts of either rubidium or cesium into these thin films further boosts device performance. At the same time, however, rubidium-doping has been observed to solve another device challenge called hysteresis, which is a variation in solar cell efficiency depending on the direction in which voltage is supplied, while cesium-doping is less effective at doing so. This point of difference raises the question as to how each type of perovskite behaves in terms of charge carrier transport—i.e. how the underlying physics of the perovskite may be changed with rubidium- or cesium-addition. In this thesis, the carrier dynamics of Rb-, Cs-, and RbCs-doped perovskite thin films were elucidated via pump-probe terahertz spectroscopy measurements, with systematic improvements for charge transport being found for all three doping conditions. The carrier mobility—or the extent to which free charges could move in response to an applied electric field—was found to be comparable between Rb-doped and Cs-doped samples. Furthermore, the carrier lifetime—or the extent to which a charge carrier remained in an excited state—was found to be the longest for RbCs hybrid samples. Furthermore, structural comparisons were made using scanning electron microscopy (SEM), which found a slight improvement in grain size for the less heavily doped Rb, Cs, and RbCs samples, as well as x-ray diffraction (XRD), which captured the steady degradation of perovskite into lead iodide over time.

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