Layered organohalide perovskite films consist of quantum wells with concentration distributions tailored to enhance charge transport. Whereas cascaded energy and charge funneling behaviors have been detected with conventional optical spectroscopies, it is not clear that such dynamics contribute to the efficiencies of photovoltaic cells. Experimental methods based on a wide range of physical principles are used to determine carrier mobilities for light-harvesting materials in photovoltaic cells. For example, in a time-of-flight experiment, carrier transport is initiated by a single pulse of light, and the timescale of carrier transport across the active layer of a device is determined. With our newly developed multidimensional Time-Of-Flight (TOF) named nonlinear photocurrent spectroscopy (NLPC), transient populations of quantum wells with different sizes are established by tuning the wavelengths of the laser pulses into their respective electronic resonances. Multidimensional TOF data suggest that such light-harvesting processes do not assist long-range charge transport due to carrier trapping at interfaces between quantum wells and interstitial organic spacer molecules. Further, the measured instantaneous drift velocities show that trap-induced carrier deceleration is more evident with higher concentrations of organic spacer cations. Overall, our measurements indicate that the majority of photocurrent is produced when the thickest quantum wells absorb light and transport carriers without charge transfer transitions involving smaller quantum wells.
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