Enhanced Photoresponse of Inkjet-Printed ZnO Thin Films Capped with CdS Nanoparticles

Abstract

Composite semiconductors provide routes for realizing high-performance electronic devices, but for many applications of such devices, low-cost manufacturing techniques are desirable. We have engineered a 3 orders of magnitude enhancement of the ultraviolet photoresponse of ZnO thin films, fabricated "in situ" by drop-on-demand inkjet printing, and then capped with CdS nanoparticles by dip coating. As a consequence, the decay time of the photoresponse is reduced to about 4 ms. Thus, capping with CdS not only suppresses the detrimental passivation layer of ZnO thin films, but also generates an interfacial carrier transport layer to reduce the probability of carrier recombination.SECTION Electron Transport, Optical and Electronic Devices, Hard Matter Z inc oxide is a versatile technologically important material for developing optical and electronic components, especially in the emerging area of transparent electronics. Availability of more advanced facilities to synthesize and characterize materials at a nanoscale has revived interest to exploit the photoconductive properties of ZnO, especially in the UV regime, although such studies have been in progress for a long time since the 1950s. 1 The intrinsic UV properties of ZnO are very useful for developing nanoscale optoelectronic devices, because it is a wide bandgap semiconductor with good carrier mobility and can be doped to become both n-, and p-type. 2,3 However, it is difficult to obtain high UV conductivity from ZnO because of the existence of surface states that give rise to a high surface recombination velocity and thereby reduce the photocurrent generation and decreases the sensitivity. 4-6 One route to effectively passivate the unwanted surface states is to develop a second semiconductor layer. From this point of view, there are as of late a few studies on charge transfer at the interface between ZnO and the surrounding ambience in composites like CdS/ZnO, 7-9 SiO 2 /ZnO, 10,11 ZnO/PVK, 12 In 2 O 3 /SnO 2 /ZnO, 13 PVP/ZnO 14 mainly to understand the photoelectrochemical properties of such systems. Recently Fang et al. 8 have found that a CdScap layer acts as a passivating layer to suppress the detrimental surface states of ZnO nanowalls, which affects the intersurface carrier transport layer and thereby enhances the UV photoconductivity at the nanowalls. We have studied this phenomenon in inkjetted ZnO films with controlled porosity and film thickness.For cost-effective fabrication of device components, inkjet printing has emerged as an attractive direct patterning technique, especially for integrated circuit applications, because of its versatility of delivering picoliter volumes of solutions or suspensions in well-defined patterns with high spatial accuracy and noncontact deposition. 15-17 Recent reports on a few studies of inkjet-printed ZnO-based nanowire fieldeffect-transistors, indicate a promising future for inkjet printing to develop device applications. 18,19 On the basis of our earlier work, 20 in this letter, we demonstrate the possibility to eng...

Structure Optimization on the Photoelectric and Photocatalytic Properties of Cu2S and ZnO Complex Films

“…Of these, Cu 2 S is considered to be promising materials as absorbers of visible light, due to its band gap energy 1.2-2.4eV [1][2]. Besides, ZnO has been a heated object in recent years, as a potential ultraviolet, blue and other visible optical device materials owing to its wide and direct band gap 3.1-3.3eV [3][4][5][6]. Additionally, polycrystalline ZnO has been found for numerous interesting applications, such as piezoelectric transducers transparent conducting lms [7][8][9][10][11].…”

Ultraviolet light sensitive In‐doped ZnO thin film field effect transistor printed by inkjet technique

“…However, the fabrication methods used so far involve multistep photolithography and vacuum‐deposition processes which contribute to their high manufacturing costs. In comparison, direct printing of inorganic materials offers the possibilities of depositing thin films using direct additive patterning processes that enable the fabrication of high‐performance and ultra low‐cost electronic components 6–8. Recently, using inkjet printing Lee et al 7, 9, 10 reported amorphous IZO‐FETs with a mobility of 7.4 cm 2 V −1 s −1 .…”

Printing ZnO Inks: From Principles to Devices

“…In particular, some intriguing studies reported on enhanced photoresponse of inkjetted ZnO thin films by embedding other NPs to improve interfacial charge transfer. Wu and coworkers [126] demonstrated that the photoconductivity of ZnO NP thin films fabricated by DOD inkjet printing (treated at 400 • C to achieve crystallization) and then capped with CdS NPs, was improved by three orders of magnitude under UV irradiation, with respect to the pure ZnO film (Figure 16a-d). The decay time was also reduced to~4 ms.…”