Thermal degradation of lead halide perovskite surfaces

Commercial use of lead halide perovskites requires improved ther mal stability and therefore a better understanding of their degrada tion mechanisms. The thermal degradation of three clean perovskite single crystal surfaces MAPbI3, MAPbBr3, FAPbBr3 was investigated using synchrotron based photoelectron spectroscopy. Central find ings are that the halide has a large impact on thermal stability and that the degradation of formamidnium results in the formation of a new organic species at the FAPbBr3 crystal surfac

The Complex Degradation Mechanism of Copper Electrodes on Lead Halide Perovskites

Lead halide perovskite solar cells have reached power conversion efficiencies during the past few years that rival those of crystalline silicon solar cells, and there is a concentrated effort to commercialize them. The use of gold electrodes, the current standard, is prohibitively costly for commercial application. Copper is a promising low cost electrode material that has shown good stability in perovskite solar cells with selective contacts. Furthermore, it has the potential to be self passivating through the formation of CuI, a copper salt which is also used as a hole selective material. Based on these opportunities, we investigated the interface reactions between lead halide perovskites and copper in this work. Specifically, copper was deposited on the perovskite surface, and the reactions were followed in detail using synchrotron based and in house photoelectron spectroscopy. The results show a rich interfacial chemistry with reactions starting upon deposition and, with the exposure to oxygen and moisture, progress over many weeks, resulting in significant degradation of both the copper and the perovskite. The degradation results not only in the formation of CuI, as expected, but also in the formation of two previously unreported degradation products. The hope is that a deeper understanding of these processes will aid in the design of corrosion resistant copper based electrode

Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping

A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite Cs_<i>x</i>FA_<i>y</i>MA_<i>z</i>Rb_{1‑<i>x</i>‑<i>y</i>‑<i>z</i>}PbBr_<i>q</i>I_3‑<i>q</i>. This paper continues this trend by exploring doping of mixed lead halide perovskites, FA_0.83MA_0.17PbBr_0.51I_2.49, with an extended set of alkali cations, i.e., Cs⁺, Rb⁺, K⁺, and Na⁺, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV–vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs⁺ can replace the organic cations in the perovskite structure, but Rb⁺, K⁺, and Na⁺ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance

Preparation of mixed ion and inorganic perovskite films using water and isopropanol as solvents for solar cell applications

CsyFA1−yPb(IxBr1−x)3 perovskite solar cells were prepared using non-hazardous solvents and metallic nitrate precursor films for the material synthesis.</p

Probing and Controlling Surface Passivation of PbS Quantum Dot Solid for Improved Performance of Infrared Absorbing Solar Cells

Surface properties of colloidal quantum dots (CQDs) are critical for the transportation and recombination of the photoinduced charge carrier in CQD solar cells, therefore dominating the photovoltaic performance. Herein, PbS CQD passivated using liquid-state ligand exchange (LSLX) and solid-state ligand exchange (SSLX) strategies are in detail investigated using photoelectron spectroscopy (PES), and solar cell devices are prepared to understand the link between the CQD surface properties and the solar cell function. PES using different energies in the soft and hard X-ray regime is applied to study the surface and bulk properties of the CQDs, and the results show more effective surface passivation of the CQDs prepared with the LSLX strategy and less formation of lead-oxide. The CQD solar cells prepared with LSLX strategy show higher performance, and the photoelectric measurements suggest that the recombination of photoinduced charges is reduced for the solar cell prepared with the LSLX approach. Meanwhile, the fabricated solar cells exhibit good stability. This work provides important insights into how to fine-tune the CQD surface properties by improving the CQD passivation, and how this is linked to further improvements of the device photovoltaic performance