Control of Photocurrent Generation in Polymer/ZnO Nanorod Solar Cells by Using a Solution-Processed TiO₂ Overlayer

Abstract

We report herein the fabrication of hybrid conjugated polymer/ZnO photovoltaic devices using ZnO nanorod structures prepared by electrodeposition and study the effect of introducing a second metal oxide overlayer using a TiCl 4 post-treatment. We use transient absorption spectroscopy, scanning electron microscopy, and photovoltaic device measurements to study the microstructure and charge generation properties of the hybrid films and the performance of the resulting devices. We show how the ZnO nanostructure can be controlled via the nanorod growth conditions and demonstrate that photovoltaic device performance can be optimized by controlling the nanostructure in this way. Moreover, we show that a large increase in photocurrent generation can be achieved by coating the ZnO surface with a thin layer of titanium oxide by treating the ZnO nanostructure with a TiCl 4 solution.SECTION Electron Transport, Optical and Electronic Devices, Hard Matter P hotovoltaic devices based on molecular and nanostructured semiconductors are an alternative to conventional inorganic solar cells. The materials used in these types of devices present several advantages, such as easy processing, mechanical flexibility, and the potential low cost of large-area fabrication. They also offer potential applications in other optoelectronic devices such as light-emitting diodes and sensors. [1][2][3] One of the more interesting advantages of hybrid solar cells based on conjugated polymers and metal oxides is the high electron mobility of the inorganic phase compared with that of available organic acceptor materials, particularly n-type polymers. An inorganic acceptor phase can be utilized to overcome the limited electron mobility in organic materials and so to help balance charge transport. 4,5 In addition, another important property of the inorganic materials is their higher physical and chemical stability relative to that of organic materials.It is well-known that the morphology and the nanostructure of the different phases that form the devices have an important influence on the final properties. 5-9 For example, in the case of the inorganic phase, there are many examples of different kinds of metal oxide nanostructures that have been successfully integrated in devices, for instance, nanoparticles, 10 nanorods, 9,11 nanotubes, 12 or mesoporous networks, 13 giving in many cases an improved photovoltaic effect relative to that of simple layered structures. 5,11 One of the most widely studied metal oxide semiconductors is zinc oxide, which is attractive for a variety of practical applications 14 due to its exceptional electrical, optical, and magnetic properties. 15 One important characteristic of ZnO is the huge family of structures that have been reported, such as nanowires, nanorods, tetrapods, and nanoribbons/belts among many others. 15 Moreover, there are several techniques that have been developed for the growth of ZnO nanostructures, including thermal evaporation, metal-organic vaporphase epitaxy (MOVPE), metal-organic chemical vapor depos...

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

“…To aid nucleation and vertical alignment a 130 nm ZnO have reported on having to cast F8BT from 10 mg/ml solutions four times via spin coating in order to create a layer thick enough to fully infiltrate their InGaN/GaN NRA [35] , but few experimental details are given in this respect in other published NR HyLED reports and complete infiltration is often presumed. There are extensive reports within hPV literature, however, that show the need for post-deposition thermal treatment to overcome wetting issues between the polymer and the NRA [20,36,37] .…”

Building on Soft Foundations: New Possibilities for Controlling Hybrid Photovoltaic Architectures

“…Attempts to address this challenge have mostly focused on morphological and microsturctural control of the active layer. [2][3][4] At present, h-PV devices are prepared either by i) deposition of the organic phase into a pre-grown metal-oxide layer, [5,6] or ii) co-deposition of both the inorganic and organic species.…”

“…Attempts to address this challenge have mostly focused on morphological and microsturctural control of the active layer. [2][3][4] At present, h-PV devices are prepared either by i) deposition of the organic phase into a pre-grown metal-oxide layer, [5,6] or ii) co-deposition of both the inorganic and organic species. [4] The deposition of highly crystalline metal-oxide directly on to any π-conjugated functional material, whilst maintaining the inherent integrity and properties of the organic layer, has yet to be demonstrated -primarily due to the elevated deposition or annealing temperatures of vacuum based processes or the requirements for substrate conductivity or harsh chemical conditions for solution-based processing methods.…”

“…Attempts to address this challenge have mostly focused on morphological and microsturctural control of the active layer. [2][3][4] At present, h-PV devices are prepared either by i) deposition of the organic phase into a pre-grown metal-oxide layer, [5,6] or ii) co-deposition of both the inorganic and organic species.[4] The deposition of highly crystalline metal-oxide directly on to any π-conjugated functional material, whilst maintaining the inherent integrity and properties of the organic layer, has yet to be demonstrated -primarily due to the elevated deposition or annealing temperatures of vacuum based processes or the requirements for substrate conductivity or harsh chemical conditions for solution-based processing methods.For PV devices two distinct architectures may be prepared, namely the conventional [17] and the so-called inverted [18] structures. The conventional geometry requires first the deposition of the organic component onto the transparent electrode, typically indium tin oxide (ITO) coated glass, followed by the deposition of the organic material and metallic electrode.…”

Synthesis of flower‐like zinc oxide and polyaniline with worm‐like morphology and their applications in hybrid solar cells

“…The large exciton binding energy (60 MeV) of ZnO has made it the suitable candidate for the exciton-related device applications compared to other wide band gap materials (e.g. Zinc oxide nanostructures such as wires, rods and tubes, and two-dimensional structures including sheets and ribbons have been synthesized [11,12] using various methods such as thermal evaporation, chemical vapor deposition, hydrothermal, etc. Zinc oxide nanostructures such as wires, rods and tubes, and two-dimensional structures including sheets and ribbons have been synthesized [11,12] using various methods such as thermal evaporation, chemical vapor deposition, hydrothermal, etc.…”