The enhancement of the fill factor in the current generation of perovskite solar cells is the key for further efficiency improvement. Thus, methods to quantify the fill factor losses are urgently needed. Two methods are presented to quantify losses due to the finite resistance of the semiconducting layers of the solar cell as well as its contacts. The first method is based on the comparison between the voltage in the dark and under illumination analyzed at equal recombination current density and results in a voltage‐dependent series resistance. Furthermore, the method reveals the existence of a strong photoshunt under illumination. The second method is based on measuring the photoluminescence of perovskite solar cells as a function of applied voltage. Thereby, the recombination current is determined as a function of voltage from short circuit to open circuit, and the presence of the photoshunt is explained with a high resistance of the electron and/or hole transport layers combined with field screening in the absorber.

Quadruple cation mixed halide perovskite, GA(0.015)Cs(0.046)MA(0.152)FA(0.787)Pb(I0.815Br0.185)(3), single crystals were grown for the first time using an inverse temperature crystallization process. Solar cell devices in n-i-p stack configuration using thin films of the same materials showed power conversion efficiency above 20%. Complementary time-resolved spectroscopy confirmed that polycrystal-line thin films and single crystals identically composed exhibit similar carrier dynamics in the picosecond range. Cooling of excited carriers and bandgap renormalization occur on the same time scale of 200-300 fs. The radiative recombination coefficient (1.2 x 10(-9) cm(3)/s) is comparable to values reported for a GaAs semiconductor. At low excitation density, a long carrier lifetime of 3.2 mu s was recorded possibly due to the passivation of recombination centers. This study clarifies discrepancies about the lifetime of hot carriers, the impact of radiative recombination, and the role of recombination centers on solar cell performance. The quadruple cation perovskites displayed short time dynamics with slow recombination of charge carriers.

Hybrid organic inorganic perovskites are ideal candidates for absorber layers in next generation thin film photovoltaics. The polycrystalline nature of these layers imposes substantial complications for the design of high efficiency devices since the optoelectronic properties can vary on the nanometre scale. Here we show via scanning tunnelling microscopy and spectroscopy that different grains and grain facets exhibit variations in the local density of states. Modeling of the tunneling spectroscopy curves allows us to quantify the density and fluctuations of surface states and estimate the variations in workfunction on the nanometre scale. The simulations corroborate that the high number of surface states leads to Fermi-level pinning of the methylammonium lead iodide surfaces. We do not observe a variation of the local density of states at the grain boundaries compared to the grain interior. These results are in contrast to other reported SPM measurements in literature. Our results show that most of the fluctuations of the electrical properties in these polycrystalline materials arise due to grain to grain variations and not due to distinct electronic properties of the grain boundaries. The measured workfunction changes at the different grains result in local variations of the band alignment with the carrier selective top contact and the varying number of surface states influence the recombination activity in the devices.

Transient photoluminescence measurements of lead-halide perovskite layers with electron or hole transport layers provide insights into the interfacial charge transfer and recombination processes. However, analytically describing these measurements over a wide range of timescales is complicated by the combination of different physical effects such as transport within the perovskite, transfer to the transport layer, accumulation of charges and recombination at the interface. Therefore, numerical driftdiffusion simulations of photoluminescence transients as a function of laser fluence and interface properties are used to obtain a quantitative understanding of experimental results. Comparison between experiment and simulation combined with an analysis of the uniqueness of the result yields an interfacerecombination velocity that has to be around 200 cm s 1 for the perovskite-PC61BM interface in order to be consistent with data obtained at several laser fluences.

The transient photoluminescence of CH3NH3PbI3/PC61BM heterojunctions is simulated numerically allowing the extraction of the interfacial recombination velocity of experimentally measured samples.

An absorber layer that does not fully cover the substrate is a common issue for thin-film solar cells such as perovskites. However, models that describe the impact of pinholes on solar cell performance are scarce. Here, we demonstrate that certain combinations of contact layers suppress the negative impact of pinholes better than others. The absence of the absorber at a pinhole gives way to a direct electrical contact between the two semiconducting electron and hole transport layers. The key to understand how pinholes impact the solar cell performance is the resulting nonlinear diodelike behavior of the current across the interface between these two layers (commonly referred to as a shunt current). Based on experimentally obtained data that mimic the current–voltage characteristics across these interfaces, we develop a simple model to predict pinhole-induced solar cell performance deterioration. We investigate typical contact layer combinations such as TiO2/spiro-OMeTAD, poly(3,4-ethylenedioxythiophene)-p...