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The device preconditioning dependent hysteresis and the consequential performance degradation hinder the actual performance and stability of the perovskite solar cells. Ion migration and charge trapping in the perovskite with large contribution from grain boundaries are the most common interpretations for the hysteresis. Yet, the high performing devices often include intermediate hole and electron transporting layers, which can further complicate the dynamical process in the device. Here, by using Kelvin Probe Force Microscopy and Confocal Photoluminescence Microscopy, we elucidate the impact of charge-transporting layers and excess MAI on the spatial and temporal variations of the photovoltage on the MAPbI3-based solar cells. By studying the devices layer by layer, we found that the light-induced ion migration occurs predominantly in the presence of an imbalanced charge extraction in the solar cells, and the charge transporting layers play crucial role in suppressing it. Careful selection and processing of the electron and hole-transporting materials are thus essential for making perovskite solar cells free from the ion migration effect.

A highly efficient organic photocatalyst (OPC) for photoinduced electron/energy-transfer reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization was identified through a systemat...

Single-walled carbon nanotubes (SWNTs) show high aspect ratio, thermal and chemical stability as well as charge mobility, and therefore appear ideally suited for improving charge extraction in organic photovoltaic (OPV) devices. Since typical charge extraction times in OPV devices are in the microsecond range, the interplay of the desired charged states with long-lived neutral states in SWNTs such as triplet excitons becomes important. Triplet excitons have recently been investigated in (6,5) SWNTs with an optical yield close to 32%. Here, we present transient absorption (TA) dynamics of (6,5)- and (7,5)-rich SWNT networks from the femtosecond to microsecond time scale. Comparing our TA spectra to results from a recent spectroelectrochemical study allows us to distinguish between contributions from charged and neutral photoexcitations. For long pump–probe delay times we identify an excess photobleach which we use as a chirality specific probe for the density of triplet excitons. We show that triplet energ...