Ultrafast laser-assisted synthesis of hydrogenated molybdenum oxides for flexible organic solar cells

Abstract

A novel method to synthesize a hydrogenated molybdenum oxide (H y MoO 3Àx ) thin film by irradiation of photons using a KrF laser (l ¼ 248 nm) on an ammonium heptamolybdate ((NH 4 ) 6 Mo 7 O 24 $4H 2 O) precursor layer is demonstrated. The laser-assisted synthesis is simple, and can be conducted in an ambient atmosphere without damaging the underlying bottom electrode and plastic substrate. The exposure time (30 ns) is extremely short compared to thermal annealing (>3 min). Because the highenergy photons are absorbed by the MoO 3 layer and provide the activation energy for the reaction, the hydrogen atoms that dissociate from the ammonium molecules bond to the MoO 3 ; this process yields a H y MoO 3Àx thin-film. By controlling the laser energy, the stoichiometry of the H y MoO 3Àx layer can be manipulated to simultaneously obtain advantageous electrical properties of both high work function (5.6 eV) and electrical conductivity (9.9 mS cm À1). The H y MoO 3Àx hole transport layer (HTL) is successfully demonstrated on flexible top-illuminated PTB7:PCBM organic solar cells (OSCs). This OSC has good mechanical flexibility, and 75% higher short-circuit current than the device with a PEDOT:PSS HTL.Finite-domain time-difference simulations were conducted to verify the enhancement of the photocurrent. The thin layer of H y MoO 3Àx was proven to be suitable for the microcavity condition which allows a resonant wavelength match to the PTB7:PCBM active layer.

Optical and Electrical Enhancement of Hydrogen Evolution by MoS2@MoO3 Core–Shell Nanowires with Designed Tunable Plasmon Resonance

“…The band at 962 cm −1 is assigned to the stretching vibration of terminal oxygen (OMo), whereas the peak at 733 cm −1 is attributed to the MoOMo vibrations of MoO 3 . When the MoO 3 is reduced with hydrogen, two new bands appear at 1141 and 3300 cm −1 , which are attributed to MoOH and OH vibration modes, respectively . In addition, the 1 H magic‐angle spinning (MAS) NMR results have been provided to further prove the formation of the H‐doped MoO 3 .…”

“…The spectrum of the pristine MoO 3 shows distinct absorption bands at 962 and 733 cm −1 . The band at 962 cm −1 is assigned to the stretching vibration of terminal oxygen (OMo), whereas the peak at 733 cm −1 is attributed to the MoOMo vibrations of MoO 3 . When the MoO 3 is reduced with hydrogen, two new bands appear at 1141 and 3300 cm −1 , which are attributed to MoOH and OH vibration modes, respectively .…”

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances

“…i) Change in photoconversion efficiency (PCE) by bending cycles at a radius of 0.48 cm. f–i) Reproduced with permission . Copyright 2016, The Royal Society of Chemistry.…”

“…Among TMOs, molybdenum oxide (MoO 3 ) has emerged as a promising candidate due to high transmittance, better air stability, and high work function (WF) . Dong et al suggested that by adopting a combination of solution processing and laser direct writing roll‐to‐roll fabrication along with the simultaneous patterning of the HTL material could be enabled (Figure f). They considered laser irradiation an alternative approach to create oxygen vacancies in MoO 3 for improving the electrical conductivity necessary for high HTL efficiency.…”

“…Laser systems operating in continuous‐wave (CW) or pulsed modes at wavelengths in the ultraviolet (UV), visible (vis), and infrared (IR) ranges have been employed to tailor the properties/functionality of metal oxides. Laser irradiation of a wide variety of MO films and nanostructures has been conducted for their applications in dielectric, ferroelectric, piezoelectric, and multiferroic magnetoelectric devices, photocatalysis, gas sensors, transparent conductors, field‐effect transistors, solar cells, and thermistors ( Figure ). Besides the overarching goal of tailoring of the physical and chemical properties, several interesting phenomena induced by laser irradiation have been reported, e.g., structural distortion and transformation, diamagnetic to ferromagnetic switching, modification of exchange bias, wettability switching, p‐type to n‐type conductivity transformation, resistive switching, metal‐to‐insulator transition (MIT), and electrochromic switching …”