NiO as Hole Transporting Layer for Inverted Perovskite Solar Cells: A Study of X‐Ray Photoelectron Spectroscopy

Abstract

Hygroscopic and acidic nature of organic hole transport layers (HTLs) insisted to replace it with metal oxide semiconductors due to their favorable charge carrier transport with long chemical stability. Apart from large direct bandgap and high optical transmittance, ionization energy in the range of −5.0 to −5.4 eV leads to use NiO as HTL due to good energetic matching with lead halide perovskites. Analyzing X‐ray photoelectron spectroscopic (XPS) data of NiO, it is speculated that p‐type conductivity is related to the NiOOH or Ni2O3 states in the structure and the electrical conductivity can be modified by altering the concentration of nickel or oxygen vacancies. However, it is difficult to separate the contribution from nonlocal screening, surface effect and the presence of vacancy induced Ni3+ ion due to very strong satellite structure in the Ni 2p XPS spectrum of NiO. Thus, an effective approach to analyze the NiO XPS spectrum is presented and the way to correlate the presence of Ni3+ with the conductivity results which will help to avoid overestimation in finding the oxygen‐rich/deficient conditions in NiO.

Nitrogen Calcination of MOF-74 Composite-Derived Materials for Enhanced Supercapacitor Performance

“…When the temperature is 300 °C, the structure of MOF-74 has not changed, which can be obtained from XRD results, so the XPS of N-1 obtains the positions of four peaks. The signals at 855.9 and 873.6 eV correspond to Ni 2p 3/2 and Ni 2p 1/2 , indicating the presence of Ni 2+ in the samples. − When the temperature is further increased, as shown in Figure f, peaks appear at 852.6 and 870.3 eV, corresponding to Ni 0 2p 3/2 and Ni 0 2p 1/2 , respectively, again proving the generation of Ni. − …”

Improving the Optoelectrical Properties of a Nickel Oxide Hole Transport Layer by Hydrogen Peroxide Treatment for Efficient Organic Solar Cells

“…Among various methods for obtaining the NiO x thin film, the combustion method has significant advantages over sol–gel, nanoparticles, electrochemical methods, and sputtering methods, which is notably simple and requires much lower processing temperatures around 150 to 200 °C. − The low process temperature not only reduces the production energy but also expands the diversity of substrates and compatibility with underlying organic layers. However, NiO x films by the combustion method still have an obstacle of insufficient surface NiOOH formation due to the presence of surface defects. − Thus, reducing the surface defects and increasing the proportion of NiOOH in the surface of the NiO x HTL are the crucial points for the high performance of NiO x -based OSCs.…”

Enhanced Conversion Efficiency in MAPbI3 Perovskite Solar Cells through Parameters Optimization via SCAPS-1D Simulation

“…CuI is chemically stable under a wide range of conditions and can be easily doped with various elements to fine-tune its electrical and optical properties [39]. P-type NiO x demonstrates a significant bandgap (greater than 3.5 eV) coupled with exceptional transparency within the visible spectrum [40]. This characteristic effectively reduces losses, including charge recombination, improves charge transport, and ensures ideal energy level alignment with diverse photoactive absorbers, attributed to its adequate conductivity and chemical stability [41][42][43].…”