Investigation of charge recombination lifetime in γ-WO3 films modified with Ag0 and Pt0 nanoparticles and its influence on photocurrent density

Abstract

In this communication, we report the growth of pure gamma-phase tungsten oxide (γ-WO 3 ) films on a conducting substrate (fluorinedoped tin oxide), followed by heat treatment at 500°C for 2 h, and finally modification with either silver (Ag 0 ) or platinum (Pt 0 ) metallic nanoparticles. These γ-WO 3 thin films can be obtained from a tungsten citrate solution by a drop-coating method, and their surfaces are modified with Ag 0 and Pt 0 nanoparticles by photoreduction. X-ray diffraction analysis indicates that all the thin films have a monoclinic structure. Field emission-scanning electron microscopy analysis reveals large and fine grains for pure γ-WO 3 film and modified WO 3 films, respectively, with an average grain size of~48 nm and thickness of~986 nm. Finally, an enhancement in photoelectrochemical performance by a factor of~2.5 is noted to modified γ-WO 3 films, which is attributed to superior electron-hole charge recombination lifetime under polychromatic irradiation. It is observed that, even under bias, an exponential reduction in photocurrent intensity is associated with charge recombination instead of mass transport conditions like diffusion. Keywords γ-WO 3 films . Ag 0 /Pt 0 nanoparticles . Recombination lifetime . Transient photocurrent

An investigation of photovoltaic devices based onp‐typeCu2Oandn‐typeγ‐WO3junction through an electrolyte solution containing a redox pair

“…We can note that the films showed negative photopotential, which is a characteristic behavior of n ‐type semiconductor. Similar results regarding this semiconductor were already discussed in works previously published by our group 56,62 …”

“…17003, with P2 1 /n space group 67 . The (002), (020), and (200) diffraction signals observed at 2θ equal to 23.14°, 23.61°, and 24.37°, respectively, are overlapped, suggesting that the films are composed of very small γ‐WO 3 particles 62 . The other planes observed in all samples were attributed to the FTO‐glass substrate, which exhibits the contribution of crystalline pattern signals associated with the SnO 2 :F phase in all samples.…”

“…The γ‐WO 3 thin films were deposited on FTO‐glass by the drop‐casting method from polymeric precursors containing tungsten. About 80 μL of the tungsten citrate precursor solution (9.3 × 10 −5 mol L −1 ) was dripped and spread on the FTO‐glass conductive surface, previously prepared by the complex polymerization (PC) method 56,62 . Then, the films were dried for 10 minutes at room temperature and heat‐treated at 500°C for 2 hours with a heating rate of 2°C minutes −1 in a muffle furnace.…”

“…Similar results regarding this semiconductor were already discussed in works previously published by our group. 56,62 From the photocurrent curves in Figure 5, we calculated the flat band potential (E fb ) values for the films. It is important to determine the E fb of a semiconductor before its application in photoelectrochemical processes 76 since from E BG and E fb values it is possible to estimate the positions of the relative CB and VB edges of the semiconductor.…”

“…This equation refers to the kinetic equation of the transient current (τ), defined by the ratio (R), R = (Jt − Jst)/(Jin − Jst), where J t is the photocurrent at time t, J st is the stationary photocurrent and J in is the photocurrent at initial time. 62,82 In this way, when a semiconductor is radiated, an initial photocurrent (J in ) peak is formed, indicating the occurrence of a charge separation process, forming an e − /h + pair. The reduction of photocurrent over time suggests the recombination process of photogenerated loads.…”