Metal halide perovskite absorber materials are about to emerge as a high-efficiency photovoltaic technology. At the same time, they are suitable for high-throughput manufacturing characterized by a low energy input and abundant low-cost materials. However, a further optimization of their efficiency, stability and reliability demands a more detailed optoelectronic characterization and understanding of losses including their evolution with time. In this work, we analyze perovskite solar cells with different architectures (planar, mesoporous, HTL-free), employing temperature dependent measurements (current–voltage, light intensity, electroluminescence) of the ideality factor to identify dominating recombination processes that limit the open-circuit voltage (V_oc). We find that in thoroughly-optimized, high-V_oc (≈1.2 V) devices recombination prevails through defects in the perovskite. On the other hand, irreversible degradation at elevated temperature is caused by the introduction of broad tail states originating from an external source (e.g. metal electrode). Light-soaking is another effect decreasing performance, though reversibly. Based on FTPS measurements, this degradation is attributed to the generation of surface defects becoming a new source of non-radiative recombination. We conclude that improving long-term stability needs to focus on adjacent layers, whereas a further optimization of efficiency of top-performing devices requires understanding of the defect physics of the nanocrystalline perovskite absorber. Finally, our work provides guidelines for the design of further dedicated studies to correctly interpret the diode ideality factor and decrease recombination losses.

Solar energy is a clean source of energy that can help fulfill the increasing global energy demand.

Organic–inorganic lead halide perovskites have emerged as very promising semiconductors with efficiencies exceeding 22% making them a serious candidate for next generation solar cells. All current high performance perovskite solar cells (PSCs), including the most recent world records, were achieved using the so-called anti-solvent method. Here, an anti-solvent, typically chlorobenzene (CB), is used to induce rapid crystallisation of a liquid perovskite precursor resulting in highly homogenous, pinhole-free planar perovskite films. While this has yielded very impressive high-performance results, few efforts have been dedicated to the fundamental understanding of the anti-solvent method. In this work, a systematic study is employed to understand the influence of anti-solvent treatment on both morphological and optoelectronic characteristics of PSCs. Perovskite absorber films were treated using CB and isopropanol (IPA) for comparing anti-solvents with different polarities. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that IPA treated perovskite films have a more uniform morphology with larger grains in comparison to CB processed perovskite films. Despite the improved morphology and solar cell performance the devices with IPA treated perovskites suffer from higher hysteresis during current density–voltage (J–V) scans. We found that this enhanced hysteresis stems mainly from higher charge accumulation at the TiO₂/perovskite interface under illumination that could also lead to formation of excess electrostatic potential contributing to an increased open circuit voltage (V_oc). Our study provides a way for in-depth spectroscopic analysis methods aiding a deeper understanding of the interfacial charge characteristics and the fundamental mechanisms of PSCs.

Down-shifting QDs together with moisture-assisted film growth enable a highly efficient and stable inverted perovskite solar cell with efficiency of over 20%.

Surface passivation of organic–inorganic halide perovskites (OIHPs) is a crucial step to annihilate the surface defects and to control the deteriorated ion migration phenomenon. Here, we study the role of lead sulfate (PbSO₄) as an effective passivator in OIHP single crystals (SCs). Using impedance spectroscopy, we evaluate the ion migration and electrical properties of lead sulfate-passivated methylammonium lead tri-bromide (MAPbBr₃) SCs. We found that the low-frequency impedance response that is assigned to the ionic motion in the MAPbBr₃ SC is strongly affected by the inorganic PbSO₄ surface treatment. The activation energy corresponding to the ion migration of MAPbBr₃ SC is increased from 0.28 to 0.36 eV after PbSO₄ surface treatment. The temperature-dependent I–V hysteresis of the MAPbBr₃ SCs upon PbSO₄ passivation was also measured. We found that such PbSO₄ surface treatment stabilizes the crystal surface and improves the hysteresis properties of the crystals at elevated temperatures.