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Optimized spin-coating and blade-coating are found to produce similar performance yet notably different morphologies.

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Here we outline a methodology for the deposition of a highly crystalline transparent conductive metal oxide (ZnO) onto a functionalised organic thin film poly (3-hexylthiophene, P3HT) without degradation of the microstructural, optical or electronic properties of the organic layer. To confirm the absence of damage we have assembled a simple bilayer photovoltaic (PV) device. The processing methodology has enabled us to demonstrate hybrid photovoltaic (h-PV) device formation in the conventional architecture for the first time. The compatibility of this novel low temperature processing route with π-conjugated molecular materials has tremendous potential for applications including electron accepting layers and optical spacers in organic PVs and light emitting diodes, as transparent electrodes and all future devices reliant on flexible substrates. Submitted to IntroductionHybrid photovoltaic (h-PV) devices combine the favourable processing and absorption characteristics of π-conjugated molecular materials with the stability and electrical properties of inorganic materials.[1] In particular, the combination of a wide band-gap metal oxide e.g.ZnO or TiO 2 with a conjugated polymer presents a pairing of materials suitable for the production of scalable, stable, nanostructured and ultimately more efficient photovoltaic devices. Despite this promise, h-PVs have yet to be prepared with efficiencies approaching even modest organic photovoltaics (OPVs). 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. The preparation of the conventional configuration is more desirable as the transparent and metallic electrodes act as hole and electron acceptors respectively. Additionally, there is no contact between the metallic electrode and the organic material -thus avoiding unwanted reactions at this interface which have been shown to have a significant contribution to cell degradation. [19, Submitted to 20]. However the processing conditions used currently for oxide deposition mean that th...

A versatile method for the deposition of transparent conducting oxide (TCO) layers directly onto conjugated polymer thin film substrates is presented. Using pulsed laser deposition (PLD) we identify a narrow window of growth conditions that permit the deposition of highly transparent, low sheet resistance aluminiumdoped zinc oxide (AZO) without degradation of the polymer film. Deposition on conjugated polymers mandates the use of low growth temperatures (<200 C), here we deposit AZO onto poly-3hexylthiophene (P3HT) thin films at 150 C, and investigate the microstructural and electrical properties of the AZO as the oxygen pressure in the PLD chamber is varied (5-75 mTorr). The low oxygen pressure conditions previously optimized for AZO deposition on rigid substrates are shown to be unsuitable, resulting in catastrophic damage of the polymer films. By increasing the oxygen pressure, thus reducing the energy of the ablated species, we identify conditions that allow direct deposition of continuous, transparent AZO films without P3HT degradation. We find that uptake of oxygen into the AZO films reduces the intrinsic charge carriers and AZO films with a measured sheet resistance of approximately 500 U , À1 can be prepared. To significantly reduce this value we identify a novel process in which AZO is deposited over a range of oxygen pressuresenabling the deposition of highly transparent AZO with sheet resistances below 50 U , À1 directly onto P3HT. We propose these low resistivity films are widely applicable as transparent top-contacts in a range of optoelectronic devices and highlight this by demonstrating the operation of a semi-transparent photovoltaic device.

A B S T R A C THere we report a simple, solution based processing route for the formation of large surface area electrodes resulting in improved organic photovoltaic devices when compared with conventional planar electrodes. The nanostructured electrode arrays are formed using hydrothermally grown ZnO nanorods, subsequently infiltrated with blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and indene-C 60 bisadduct (IC 60 BA) as photoactive materials. This well studied organic photoactive blend allows the composition/processing/performance relationships to be elucidated. Using simple solution based processing the resultant nanostructured devices exhibited a maximum power conversion efficiency (PCE) of 2.5% compared with the best planar analogues having a PCE of around 1%. We provide detailed structural, optical and electrical characterization of the nanorod arrays, active layers and completed devices giving an insight into the influence of composition and processing on performance. Devices were fabricated in the desirable inverse geometry, allowing oxidation resistant high work-function top electrodes to be used and importantly to support the hydrothermal growth of nanorods on the bottom electrode -all processing was carried out under ambient conditions and without the insertion of a hole transport layer below the anode. The nanorods were successfully filled with the active layer materials by carrying out a brief melt processing of a spin-cast top layer followed by a subsequent thermal anneal which was identified as an essential step for the fabrication of operational devices. The growth method used for nanorod fabrication and the active layer processing are both inherently scalable, thus we present a complete and facile route for the formation of nanostructured electron acceptor layers that are suitable for high performance organic active layers.

Abstract. The formation of a well-defined, reproducible ZnO nanorod scaffold for hybrid photovoltaic applications has been investigated. A standard hydrothermal growth method was used and the influence of chemical additions in controlling length, width, density, and orientation was studied. The nanostructures prepared have been characterized by scanning electron microscopy, x-ray diffraction, UV-visible spectroscopy in addition to measurement of the wetting behavior. A standard procedure for the production of vertically orientated nanorods with a narrow size distribution, high areal density, and good wettability in aqueous solutions is presented. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

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