An embedded interfacial network stabilizes inorganic CsPbI3 perovskite thin films.

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into otherwise-unstable CsPbI3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

All-Evaporated, All-Inorganic CsPbI3 Perovskite-Based Devices for Broad-Band Photodetector and Solar Cell Applications.

Following the rapid increase of organic metal halide perovskites toward commercial application in thin-film solar cells, inorganic alternatives attracted great interest with their potential of longer device lifetime due to the stability improvement under increased temperatures and moisture ingress. Among them, cesium lead iodide (CsPbI3) has gained significant attention due to similar electronic and optical properties to methylammonium lead iodide (MAPbI3), with a band gap of 1.7 eV, high absorption coefficient, and large diffusion length, while also offering the advantage of being completely inorganic, providing a higher thermal stability and preventing material degradation. On a device level, however, it seems also essential to replace organic transport layers by inorganic counterparts to further prevent degradation. In addition, devices are mostly fabricated by spin coating, limiting their reproducibility and scalability; in this case, exploring all-evaporated devices allows us to improve the quality of the layers and to increase their reproducibility. In this work, we focus on the deposition of CsPbI3 by CsI and PbI2 co-evaporation. We fabricate devices with an all-inorganic, all-evaporated structure, employing NiO and TiO2 as transport layers, and evaluate these devices for both photodetector and solar cell applications. As a photodetector, low leakage current, high external quantum efficiency (EQE) and detectivity, and fast rise and decay times were obtained, while as a solar cell, acceptable efficiencies were achieved. These all-inorganic, all-evaporated devices represent one step forward toward higher stability and reproducibility while enabling large area compatibility and easier integration with other circuitry and, in future, the possible commercialization of perovskite-based technology.

Solid-State Neutron Detection Based on Methylammonium Lead Bromide Perovskite Single Crystals.

Perovskite-based semiconductors, such as methylammonium and cesium lead halides (MPbX3: M = CH3NH3+ or Cs+; X = I-, Br-, or Cl-), have attracted immense attention for several applications, including radiation detection, due to their excellent electronic and optical properties.1,2,3,4,5,6 In addition, the combination of perovskites with other materials enables unique device structures. For example, robust and reliable diodes result when combined with metal oxide semiconductors. This device can be used for detection of nonionizing and ionizing radiation. In this paper, we report a unique perovskite single-crystal-based neutron detector using a heterojunction diode based on single-crystal MAPbBr3 and gallium oxide (Ga2O3) thin film. The MAPbBr3/Ga2O3 diodes demonstrate a leakage current of ∼7 × 10-10 A/mm2, an on/off ratio of ∼102, an ideality factor of 1.41, and minimal hysteresis that enables alpha particle, gamma-ray, and neutron detection at a bias as low as (-5 V). Gamma discrimination is further improved by 85% by optimizing the thickness of the perovskite single crystal. The MAPbBr3/Ga2O3 diodes also demonstrate a neutron detection efficiency of ∼3.92% when combined with a 10B neutron conversion layer.

Controlling Carrier Type and Concentration in NiO Films To Enable in Situ PN Homojunctions.

The oxygen partial pressure during NiO deposition in reactive sputtering of a Ni target is used to control its carrier type and concentration, obtaining both n- and p-type films. Carrier concentration can be controlled, ranging from 1019 to 1014 cm-3. Films deposition is performed at 200 °C, a relatively low temperature that enables the use of glass as substrate. Experimental band diagrams for n-type NiO are obtained for the first time. Finally, a NiO homojunction is demonstrated by introducing a low carrier concentration layer in between n- and p+-type NiO layers. Layers are deposited in situ, preventing contamination and improving the interface quality, as observed by TEM. The Ni:O ratio for each layer was also obtained by analytical TEM measurements, demonstrating the impact of the oxygen partial pressure on the films' stoichiometry and the simplicity of our process to control carrier type and carrier concentration in oxide semiconductors.

Tunable Electrical and Optical Properties of Nickel Oxide (NiO x) Thin Films for Fully Transparent NiO x-Ga2O3 p-n Junction Diodes.

One of the major limitations of oxide semiconductors technology is the lack of proper p-type materials to enable devices such as pn junctions, light-emitting diodes, and photodetectors. This limitation has resulted in an increased research focus on these materials. In this work, p-type NiO x thin films with tunable optical and electrical properties as well as its dependence with oxygen pressure during pulsed laser deposition are demonstrated. The control of NiO x films resistivity ranged from ∼109 to ∼102 Ω cm, showing a p-type behavior with Eg tuning from 3.4 to 3.9 eV. Chemical composition and the resulting band diagrams are also discussed. The all-oxide NiO x-Ga2O3 pn junction showed very low leakage current, an ideality factor of ∼2, 105 on/off ratio, and 0.6 V built-in potential. Its J- V temperature dependence is also analyzed. C- V measurements demonstrate diodes with a carrier concentration of 1015 cm-3 for the Ga2O3 layer, which is fully depleted. These results show a stable, promising diode, attractive for future photoelectronic devices.