2, University of California, Santa Barbara, Santa Barbara, California, United States
Understanding charge dynamics in semiconductors for solar cells is critical to their identification, development and potential commercial implementation. Optical spectroscopic techniques such as photoluminescence spectroscopy, transient absorption spectroscopy, time-resolved microwave conductivity and terahertz spectroscopy are traditionally employed to elucidate optoelectronic properties in these systems. Yet many such techniques involve high-power optical sources and photo-generated carrier densities many orders of magnitude higher than present under typical solar cell operating conditions. An alternative approach is to study carrier dynamics using steady-state illumination rather than with high-fluence pulsed optical sources. In this presentation I describe a simple and versatile contactless technique to study the photoconductivity of a semiconductor, as function of incident optical power-density, at optical power densities ≤ 1 sun. By employing thin solution-processed films of the highly-studied, high-performance hybrid-halide perovskite methylammonium lead iodide ((MA)PbI3), I evaluate a proxy for mobility-lifetime product, with a strong dependence on incident optical power densities even below 1 mW/cm2.