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

Generation, transport, and detection of valley-locked spin photocurrent in WSe2-graphene–Bi2Se3 heterostructures

Quantum optoelectronic devices capable of isolating a tar-get degree of freedom (DoF) from other DoFs have allowed for new applications in modern information technology. Many works on solid-state spintronics have focused on methods to disentangle the spin DoF from the charge DoF1, yet many related issues remain unresolved. Although the recent advent of atomically thin transition metal dichalcogenides (TMDs) has enabled the use of valley pseudospin as an alternative DoF2,3, it is nontrivial to separate the spin DoF from the valley DoF since the time-reversal valley DoF is intrinsically locked with the spin DoF4. Here, we demonstrate lateral TMD?밽ra-phene?뱓opological insulator hetero-devices with the possibil-ity of such a DoF-selective measurement. We generate the valley-locked spin DoF via a circular photogalvanic effect in an electric-double-layer WSe2 transistor. The valley-locked spin photocarriers then diffuse in a submicrometre-long gra-phene layer, and the spin DoF is measured separately in the topological insulator via non-local electrical detection using the characteristic spin?뱈omentum locking. Operating at room temperature, our integrated devices exhibit a non-local spin polarization degree of higher than 0.5, providing the potential for coupled opto-spin?뱕alleytronic applications that indepen-dently exploit the valley and spin DoFs