ZnO thin films fabricated by chemical bath deposition, used as buffer layer in organic solar cells (original) (raw)
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Solar Energy, 2018
Interfacial buffer layers such as electron and hole transporting layers are crucial in maximizing power conversion efficiencies of organic solar cell (OSC) devices. In this manuscript, we studied the role of solution processed ZnO as electron transport layer in devices with Aluminum (Al) cathode on opaque substrates in inverted device configuration where Al and Gold (Au) are used as cathode and anode, ZnO and MoO 3 are used as electron and hole transport layers respectively whilst P3HT:PC 60 BM is used as active layer (ActL). The results show that a thin layer of Aluminum Oxide (Al 2 O 3) present on thermally evaporated Al cathode acts as an electron transport layer (ETL) when ZnO is absent, with surface states present on Al 2 O 3 layer aiding the electron transport to cathode. The presence of ZnO as ETL between Al and active layer leads to a decrease in the efficiency of solar cell from 2.9% to 1.9%, attributed to the trapping of electrons at Al/ZnO interface due to unfavourable band alignment created by the presence of composite Al 2 O 3 /ZnO layer, implying that an additional ETL is not required when Al is used as a bottom electrode and could be an added advantage due to reduced processing steps.
A Transparent Electrode Based on Solution-Processed ZnO for Organic Optoelectronic Devices
Nature Communications
Achieving high-efficiency indium tin oxide (ITO)-free organic optoelectronic devices requires the development of high-conductivity and high-transparency materials for being used as the front electrode. Herein, sol-gel-grown zinc oxide (ZnO) films with high conductivity (460 S cm−1) and low optical absorption losses in both visible and near-infrared (NIR) spectral regions are realized utilizing the persistent photoinduced doping effect. The origin of the increased conductivity after photo-doping is ascribed to selective trapping of photogenerated holes by oxygen vacancies at the surface of the ZnO film. Then, the conductivity of the sol-gel-grown ZnO is further increased by stacking the ZnO using a newly developed sequential deposition strategy. Finally, the stacked ZnO is used as the cathode to construct ITO-free organic solar cells, photodetectors, and light emitting diodes: The devices based on ZnO outperform those based on ITO, owing to the reduced surface recombination losses at...
Organic Photovoltaic Cells Based on ZnO Thin Film Electrodes
Journal of Nanoscience and Nanotechnology, 2010
Due to its wide band-gap (ca. 3.4 eV), ZnO is a possible candidate material to be used as transparent electrode for a new class of photovoltaic (PV) cells. Also, an increased interest for the photovoltaic properties of several organic monomers and polymers (merocyanines, phthalocyanines and porphyrins) was noticed, because of their high optical absorption in the visible region of the spectrum allowing them to be used as potential inexpensive materials for solar cells. Preparation and properties of CuPc (copper phthalocyanine) based photovoltaic cells using ZnO thin films as transparent conductor electrodes are presented in this paper. ZnO layers are grown by pulsed laser deposition, while the organic layers are obtained by thermal evaporation. Structural characterization is performed by electron microscopy. Optical and transport properties of the mutilayered structures are obtained by electrical and spectro-photometric measurements. The influence of the ZnO-polymer interface on the external quantum efficiency (EQE) of the photovoltaic cell is clearly evidenced by our measurements.
ACS Applied Materials & Interfaces, 2015
The role of cathode buffer layer (CBL) is crucial in determining the power conversion efficiency (PCE) of inverted organic solar cells (IOSCs). The hallmarks of a promising CBL include high transparency, ideal energy levels and tendency to offer good interfacial contact with the organic bulk-heterojunction (BHJ) layers. Zinc oxide (ZnO), with its ability to form numerous morphologies in juxtapose to its excellent electron affinity, solution processability, and good transparency is an ideal CBL material for IOSCs. Technically, when CBL is sandwiched between the BHJ active layer and the indium-tin-oxide (ITO) cathode, it performs two functions viz, electron collection from the photoactive layer that is effectively carried out by morphologies like nanoparticles or nanoridges obtained by ZnO sol-gel (ZnO SG) method through an accumulation of individual nanoparticles and secondly, transport of collected electrons towards the cathode, which is more effectively manifested by 1D nanostructures like ZnO nanorods (ZnO NRs). This work presents the use of bilayered ZnO CBL in IOSCs of poly (3-hexylthiophene) (P3HT): [6, 6]-phenyl-C 60 -butyric acid methyl ester (PCBM) to overcome the limitations offered by a conventionally used single layer CBL. We found that the PCE of IOSCs with an appropriate bilayer CBL comprising of ZnO NRs-ZnO SG is ~18.21% higher than those containing ZnO SG-ZnO NRs. We believe that, in bilayer ZnO NRs-ZnO SG, ZnO SG collects electrons effectively from photoactive layer while ZnO NRs transport them further to ITO resulting significant increase in the photocurrent to achieve highest PCE of 3.70%. The enhancement in performance was obtained through improved interfacial engineering, enhanced electrical properties and reduced surface/bulk defects in bilayer ZnO NRs-ZnO SG. This study demonstrates that the novel bilayer ZnO CBL approach of electron collection/transport would overcome crucial interfacial recombination issues and contribute in enhancing PCE of IOSCs.
ACS Applied Materials & Interfaces, 2015
Surface treatments of various layers in organic solar cells play a vital role in determining device characteristics. In this manuscript, we report on the influence of surface treatment of indium tin oxide (ITO) electrode and of electron transport layer (ETL), ZnO, on the photovoltaic performance of inverted organic solar cells (IOSC) and their correlation with the surface chemistry and surface potential as studied using X-ray photoelectron spectroscopy and Kelvin probe force microscopy, using a device structure Glass/ ITO/ ZnO / P3HT: PCBM / MoO3 / Au or Ag (P3HT: Poly(3-hexylthiophene-2,5-diyl), PCBM: Phenyl-C61butyric acid methyl ester). Our results show that while ozonization of ITO leads to an improvement in the device power conversion efficiency, ozonization of subsequent ZnO layer results in a decreased performance, mainly due to decrease in the fill factor (FF). However, subsequent methanol (CH3OH) treatment of ZnO layer on ozonized ITO electrode shows substantial improvement with device efficiencies exceeding ~ 4% along with superior reproducibility of the devices. Further, a detailed analysis of the surface wettability, chemistry and surface potential using contact angle measurements, X-ray photoelectron spectroscopy (XPS), Kelvin probe force microscopy (KPFM) attribute the improvements to the elimination of surface defects and the changes in the surface potential. Finally, impedance analysis suggests that methanol treatment of the ZnO layers leads to the development of a favorable nano-phase structure having higher conductivity, which is otherwise indiscernible using microscopic methods.
Organic solar cells on indium tin oxide and aluminum doped zinc oxide anodes
Applied Physics Letters, 2007
The authors compare organic solar cells using two different transparent conductive oxides as anode: indium tin oxide ͑ITO͒ and three kinds of aluminum doped zinc oxide ͑ZAO͒. These anodes with different work functions are used for small molecule photovoltaic devices based on an oligothiophene derivative as donor and fullerene C 60 as acceptor molecule. It turns out that cells on ITO and ZAO have virtually identical properties. In particular, the authors demonstrate that the work function of the anode does not influence the V oc of the photovoltaic device due to the use of doped transport layers.