Erin E. Perry

Power Factor Enhancement in Solution‐Processed Organic n‐Type Thermoelectrics Through Molecular Design

A new class of high-performance n-type organic thermoelectric materials, self-doping perylene diimide derivatives with modified side chains, is reported. These materials achieve the highest n-type thermoelectric performance of solution-processed organic materials reported to date, with power factors as high as 1.4 μW/mK(2). These results demonstrate that molecular design is a promising strategy for enhancing organic thermoelectric performance.

Electronic structure and photovoltaic application of BiI3

Rapid recent improvement in photovoltaic efficiency in hybrid lead halide perovskite materials has provided the impetus for understanding other, related main-group halide systems. Here, we show that the closely related but less toxic bismuth iodide BiI3 can show promising optoelectronic properties. Layered binary BiI3 is used here as the active layer in planar solar cell architectures (efficiency approximately 0.3%). Experimental and computational studies of absolute band positions of BiI3 are also presented, to help in the rational design of device architectures that would allow efficient charge transfer at the interfaces.

Temperature-Dependent Polarization in Field-Effect Transport and Photovoltaic Measurements of Methylammonium Lead Iodide

While recent improvements in the reported peak power conversion efficiency (PCE) of hybrid organic-inorganic perovskite solar cells have been truly astonishing, there are many fundamental questions about the electronic behavior of these materials. Here we have studied a set of electronic devices employing methylammonium lead iodide ((MA)PbI3) as the active material and conducted a series of temperature-dependent measurements. Field-effect transistor, capacitor, and photovoltaic cell measurements all reveal behavior consistent with substantial and strongly temperature-dependent polarization susceptibility in (MA)PbI3 at temporal and spatial scales that significantly impact functional behavior. The relative PCE of (MA)PbI3 photovoltaic cells is observed to reduce drastically with decreasing temperature, suggesting that such polarization effects could be a prerequisite for high-performance device operation.

Charge transport in a two-dimensional hybrid metal halide thiocyanate compound

Solution-processable organic metal halide compounds, such as methylammonium lead iodide (CH3NH3PbI3), possess unique optical and electronic properties such as long carrier lifetimes and high charge carrier mobility. Here we study a layered, 2-dimensional hybrid halide compound: methylammonium lead thiocyanate iodide ((CH3NH3)2Pb(SCN)2I2). Films deposited from solution are observed to grow with strong preferential alignment of 2-dimensional layers parallel to the substrate. The charge-transport properties of carriers in the 2-dimensional planes of (CH3NH3)2Pb(SCN)2I2 were measured using the contactless electronic characterization technique time-resolved microwave conductivity (TRMC). TRMC measurements show that the sum of the electron and hole charge carrier mobilities in (CH3NH3)2Pb(SCN)2I2 is above 1 cm2 V−1 s−1 and that the carrier lifetime is relatively long.

Steady-state microwave conductivity reveals mobility-lifetime product in methylammonium lead iodide

Many time-resolved techniques to study charge carrier recombination involve pulsed high-power optical excitation and photo-generated carrier densities many orders of magnitude higher than present under typical solar cell operating conditions. In this report, we demonstrate a steady-state contactless microwave conductivity technique to evaluate the photoconductivity of carriers in semiconductors at low illumination intensity, as a function of optical power density. We studied characteristics of both thin films and single crystals of a hybrid halide perovskite compound, methylammonium lead iodide (MAPbI3). The aggregate mobility-lifetime product of majority and minority carriers in thin films of MAPbI3 was determined and found to be highly-dependent on incident optical power density, even at sub-1-sun illumination intensities, and attributed to trap states within the films.Many time-resolved techniques to study charge carrier recombination involve pulsed high-power optical excitation and photo-generated carrier densities many orders of magnitude higher than present under typical solar cell operating conditions. In this report, we demonstrate a steady-state contactless microwave conductivity technique to evaluate the photoconductivity of carriers in semiconductors at low illumination intensity, as a function of optical power density. We studied characteristics of both thin films and single crystals of a hybrid halide perovskite compound, methylammonium lead iodide (MAPbI3). The aggregate mobility-lifetime product of majority and minority carriers in thin films of MAPbI3 was determined and found to be highly-dependent on incident optical power density, even at sub-1-sun ...