Electrochemical Impedance Spectroscopy of All-Perovskite Tandem Solar Cells

This work explores electrochemical impedance spectroscopy to study recombination and ionic processes in all-perovskite tandem solar cells. We exploit selective excitation of each subcell to enhance or suppress the impedance signal from each subcell, allowing study of individual tandem subcells. We use this selective excitation methodology to show that the recombination resistance and ionic time constants of the wide gap subcell are increased with passivation. Furthermore, we investigate subcell-dependent degradation during maximum power point tracking and find an increase in recombination resistance and a decrease in capacitance for both subcells. Complementary optical and external quantum efficiency measurements indicate that the main driver for performance loss is the reduced capacity of the recombination layer to facilitate recombination due to the formation of a charge extraction barrier. This methodology highlights electrochemical impedance spectroscopy as a powerful tool to provide critical feedback to unlock the full potential of perovskite tandem solar cells

Robust and Recyclable Substrate Template with an Ultrathin Nanoporous Counter Electrode for Organic-Hole-Conductor-Free Monolithic Perovskite Solar Cells

A robust and recyclable monolithic substrate applying all-inorganic metal-oxide selective contact with a nanoporous (np) Au:NiO_<i>x</i> counter electrode is successfully demonstrated for efficient perovskite solar cells, of which the perovskite active layer is deposited in the final step for device fabrication. Through annealing of the Ni/Au bilayer, the nanoporous NiO/Au electrode is formed in virtue of interconnected Au network embedded in oxidized Ni. By optimizing the annealing parameters and tuning the mesoscopic layer thickness (mp-TiO₂ and mp-Al₂O₃), a decent power conversion efficiency (PCE) of 10.25% is delivered. With mp-TiO₂/mp-Al₂O₃/np-Au:NiO_<i>x</i> as a template, the original perovskite solar cell with 8.52% PCE can be rejuvenated by rinsing off the perovskite material with dimethylformamide and refilling with newly deposited perovskite. A renewed device using the recycled substrate once and twice, respectively, achieved a PCE of 8.17 and 7.72% that are comparable to original performance. This demonstrates that the novel device architecture is possible to recycle the expensive transparent conducting glass substrates together with all the electrode constituents. Deposition of stable multicomponent perovskite materials in the template also achieves an efficiency of 8.54%, which shows its versatility for various perovskite materials. The application of such a novel NiO/Au nanoporous electrode has promising potential for commercializing cost-effective, large scale, and robust perovskite solar cells

Thermal Reaction of 2,4-Dibromopyridine on Cu(100)

Nitrogen-containing aromatics have potential applications in surface functionalization, corrosion inhibition, and carbon-nitride materials. Reflection–absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and temperature-programmed reaction/desorption (TPR/D) have been employed to study the system of 2,4-C₅NH₃Br₂/Cu­(100). Our experimental results indicate that 2,4-C₅NH₃Br₂ is adsorbed predominantly in molecular form on Cu(100) at 100 K; however, a tiny fraction of the adsorbed molecules is subjected to debromination. The 2,4-C₅NH₃Br₂ undergoes partial C–Br dissociation below 400 K, forming C₅NH₃Br intermediate. Although after breaking both the C–Br bonds (>400 K), 2,4-pyridyne (C₅NH₃) can be formed, the possibility of Ullmann coupling reaction cannot be excluded. The NEXFAS study shows a ∼ 35° average inclination of the aromatic plane, with respect to the surface, in a packed 2,4-pyridyne adsorption layer. Thermal decomposition of the C₅NH₃ or its coupling reaction products on the Br/Cu(100) surface mainly occurs at a temperature higher than 550 K, generating H₂, HCN, HBr, and (CN)₂