Careful interpretation of time-resolved photoluminescence (TRPL) measurements can substantially improve our understanding of the complex nature of charge-carrier processes in metal-halide perovskites, including, for instance, charge separation, trapping, and surface and bulk recombination. In this work, we demonstrate that TRPL measurements combined with powerful analytical models and additional supporting experiments can reveal insights into the charge-carrier dynamics that go beyond the determination of minority-charge-carrier lifetimes. While taking into account doping and photon recycling in the absorber layer, we investigate surface and bulk recombination (trap-assisted, radiative, and Auger) by means of the shape of photoluminescence transients. The observed long effective lifetime indicates high material purity and good passivation of perovskite surfaces with exceptionally low surface recombination velocities on the order of about 10 cm=s. Finally, we show how to predict the potential open-circuit voltage for a device with ideal contacts based on the transient and steady-state photoluminescence data from a perovskite absorber film and including the effect of photon recycling.

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The interaction between conduction electrons and paramagnetic ions in metals has been investigated by observation pf the paramagnetic resonance pf gadolinium in alloys and intermetallic compounds. Spectra of Gd in powdered samples were observed at temperatures between 1. 4 and 500'K and frequencies between 10 and 80 kMc/sec. A single line has been observed with g values varying between 2.01 and 1.88. A striking correlation has been established between the g shifts and the susceptibility and the specific heat of the pure Rh-Pd and Pd-Ag alloys, leading tp the conclusion that the shifts are due to the interaction of the host conduction electrons with the paramagnetic ions. Linewidth cpnsideratipns indicate that this interaction is mostly of scalar form. From the observed dependence pf the g shift and linewidth on the magnetization we conclude that the interaction produces the electron Knight shift predicted by Yosida, rather than the shift predicted by Kittel and Mitchell. The observed negative shift indicates that there is a polarization of mostly negative sign in agreement with previous nuclear magnetic resonance observations on GdA12 by Jaccarino et al. A possible mechanism fpr this negative polarizatipn is the Anderson-Clogston mechanism. Some experiments on line brpadening due to different magnetic species, and their connectipn to the absence of the g shift of Gd and Mn in Ag are discussed briefly.

Hematite (α-Fe 2 O 3) is known for poor electronic transport properties, which are the main drawback of this material for optoelectronic applications. In this study, we investigate the concept of enhancing electrical conductivity by the introduction of oxygen vacancies during temperature treatment under low oxygen partial pressure. We demonstrate the possibility of tuning the conductivity continuously by more than five orders of magnitude during stepwise annealing in a moderate temperature range between 300 and 620 K. With thermoelectric power measurements, we are able to attribute the improvement of the electrical conductivity to an enhanced charge-carrier density by more than three orders of magnitude. We compare the oxygen vacancy doping of hematite thin films with hematite nanoparticle layers. Thereby we show that the dominant potential barrier that limits charge transport is either due to grain boundaries in hematite thin films or due to potential barriers that occur at the contact area between the nanoparticles, rather than the potential barrier within the small polaron hopping model, which is usually applied for hematite. Furthermore, we discuss the transition from oxygen-deficient hematite α-Fe 2 O 3−x towards the magnetite Fe 3 O 4 phase of iron oxide at high density of vacancies.

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