L. Cattin

MoO3 surface passivation of the transparent anode in organic solar cells using ultrathin films

An original surface passivation technique of indium tin oxide (ITO) used as anode in organic solar cells is proposed. We demonstrate that a thin MoO3 film (3.5±1 nm) at the interface ITO/organic donor allows improving significantly the devices’ performances. The devices are based on the multiheterojunction structure copper phthalocyanine (CuPc)/fullerene (C60)/aluminum tris(8-hydroxyquinoline) (Alq3). The deposition of MoO3 onto ITO improves the charge transfer from CuPc to ITO. The enhancement in the hole collection efficiency in the presence of an oxide layer can be explained in terms of the reduction in the effective barrier against hole transfer from CuPc into the ITO anode. The contact ITO/MoO3/CuPc behaves like a metal-insulator-semiconductor (MIS) structure, which allows reducing the energy barrier due to the difference between the work function of ITO and the highest occupied molecular orbital of CuPc. It is shown that the optimum MoO3 thickness corresponds to a compromise between an optimum ITO c...

Improvement of organic solar cell performances using a zinc oxide anode coated by an ultrathin metallic layer

The authors have achieved an efficient organic solar cell based on copper phthalocyanine (CuPc) layer as donor and fullerene (C60) as acceptor. The aluminum doped zinc oxide (ZnO:Al) instead of indium tin oxide (ITO) is used as the anode. An ultrathin gold film is introduced among ZnO:Al, transparent conductor oxide, and the CuPc donor layer. We show that the power conversion efficiency of this cell is enhanced by one order of magnitude compared to that achieved with a ZnO anode without ultrathin gold film. Therefore, the power conversion efficiency of this cell is comparable to that with an ITO anode.

Effect of the thickness of the MoO3 layers on optical properties of MoO3/Ag/MoO3 multilayer structures

The electrical and optical properties of MoO3/Ag/MoO3 multilayer structures have been studied using the Ag deposition rate and layer thicknesses as parameters. When the silver film is deposited at 0.20 nm/s rate, the silver layer thickness necessary to achieve the percolation threshold of the resistivity ρ towards conductive structures is 10 nm. Below 10 nm, the films are semiconductor and above the films are conductors. In the present work, the variation of the thicknesses of top and bottom MoO3 layers is shown to strongly modify the optical properties of the multilayer structures. By using a Ag thickness of 10 nm, we demonstrate an increasing of the transmittance of the MoO3/Ag/MoO3 structures by optimizing the MoO3 layers thicknesses. When the MoO3 bottom layer is 20 nm thick, and the MoO3 top layer is 35 nm, the maximum transmission is 86% at the wavelength of 465 nm, while the averaged transmission in the visible range (350 nm-800 nm) is 70%. The best measured conductivity, σ = 1.1 × 105 (Ω cm)-1, corresponds also to this MoO3 (20 nm)/Ag (10 nm)/MoO3 (35 nm) structure. A good qualitative agreement between the theoretical calculations of the variation of the optical transmittance and reflectance of the MoO3/Ag/MoO3 structures is also highlighted.

MoO3/Ag/MoO3 anode in organic photovoltaic cells: Influence of the presence of a CuI buffer layer between the anode and the electron donor

MoO3/Ag/MoO3 (MAM) multilayer structures (layers thickness 20 nm/10 nm/35 nm) are used as anode in CuPc/C60/Alq3/Al organic photovoltaic cells. The averaged transmittance (400 nm-800 nm) of these MoO3/Ag/MoO3 multilayer structures is 70% ± 2% and their sheet resistance is 3.5 ± 1.0 Ω/sq. When these multilayer structures are used as anode, the power conversion efficiency of the MoO3/Ag/MoO3/CuPc/C60/Alq3/Al cells is around 1%, this efficiency is increased of 50% when a thin CuI film (3 nm) is introduced at the interface between the anode and the organic film. This improvement is attributed to the templating effect of CuI on the CuPc molecules.

Current-voltage (I-V) studies of Mo/γ-In2Se3/ZnO : Al diode structures

Mo/?-In2Se3/ZnO?:?Al diode structures have been grown by vacuum deposition. In order to study the influence of the ZnO?:?Al electrode on the diode properties, ZnO?:?Al conductive and insulating films have been deposited by rf magnetron sputtering using a single Al2O3 doped ZnO target. These films have been characterized before their use in diodes. The electrical properties of ZnO?:?Al are controlled by the oxygen partial pressure during deposition. The effect of the composition on the I?V characteristics of ?-In2Se3 based diodes has been investigated. When ?-In2Se3 is doped with manganese there is no photovoltaic effect while there is when it is pure. It is shown that the I?V curves agree with Schottky theory only in the case of pure ?-In2Se3. When it is doped the I?V curves agree well with the trap-controlled space charge limited transport theory, which is attributed to the presence of a band of localized states present in the band gap of ?-In2Se3 after Mn doping.

Organic Solar Cells Performances Improvement Induced by Interface Buffer Layers

J. C. Bernede1, A. Godoy2, L. Cattin1, F. R. Diaz3, M. Morsli1 and M. A. del Valle3 1Universite de Nantes, Nantes Atlantique Universites, LAMP, EA 3825, Faculte des Sciences et des Techniques, 2 rue de la Houssiniere, BP 92208, Nantes, F-44000 2Facultad Ciencias de la Salud, Universidad Diego Portales. Ejercito 141. Santiago de Chile 3Facultatd de Quimica, PUCC, Casilla 306, Correo 22, Santiago, 1France 2,3Chile

Small molecules organic photovoltaic devices based on the planar heterojunction porphyrin derivates/fullerene

In this paper, we studied of photoelectric properties of multilayer organic photovoltaic cells (OPV cells). The active organic layers consisted of a planar heterojunction between a layer of (meso-tetrakis(5-bromo-2-thienyl)porphyrin), (TBrTP) as electron donor (ED) and a layer fullerene molecules. For the manufacture of photovoltaic devices we use a the technique of high vacuum by thermal sublimation that allows multilayer devices realization easily by successive depositions, and it does not require solvents, achieving purer films with reproducible characteristics. The TBrTP allows achieving OPVCs exhibiting promising efficiencies when the ABL is the MoO3/CuI DABL. The CuI improves the current in the organic layer by one order of magnitude, which allows decreasing the series resistance of the OPVCs and therefore improving the OPVCs.

J–V characteristics of dark and illuminated classical and inverted organic solar cells based on the CuPc/C60 heterojunction

A comparison of the performances of classical and inverted organic solar cells based on the junction copper phthalocyanine/fullerene (CuPc/C60) shows that the former devices give the best efficiency. The transport properties of charge carriers in the organic material and the interface properties have been investigated using a mathematical simulation taking into account the effect of bulk and interface properties. Good agreement between experimental and calculated values can be achieved using different parameter values following the type of solar cells. In classical solar cells, the current is space charge limited, while there is no barrier at the contact electrode/organic material. In the case of inverted solar cells it is necessary to introduce a barrier contact at these interfaces to achieve a good fit between experimental and theoretical values. Therefore, the lower efficiency of the inverted solar cells is due to the barrier contact at the interface and smaller electrode work function difference.

Synthesis and optical behavior of PLED devices based on (PMMA)/(PAA)/Er(AP) 6 Cl 3 complex and N,N′ -didodecyl-3,4,9,10-perylene tetracarboxylic diimide composites

The realization of efficient polymeric light emitting diode (PLEDs) in a double-layered configuration was investigated. The devices are composed by transparent conductive oxide (ITO)/MoO3/organic layers/aluminum/selenium, conformed by thin film sandwich structures obtained by vacuum evaporation. Two organic layers were developed. First a n-type organic layer of composite based on polymethylmethacrylate (PMMA)/polyacrilic acid (PAA)/Er(AP)6Cl3 complex and second a n-type organic semiconductor, N,N′-didodecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C12H25). The rare earth complex composites and the perilenic compound were synthesized and characterized using UV–Visible absorption, XPS, and NMR techniques, respectively. Driving voltage of devices was lowered by applying MoO3 thin film as buffer layer and high current intensity efficiency was obtained applying a perilenic film. The effect of MoO3 and PTCDI-C12H25 thin films, on the optical and the physical properties of the electroluminescent devices were discussed. I–V measurements have shown that the structures exhibit diode characteristics and the electroluminescent signal increases when PTCDI-C12H25 thin layer is introduced between the anode and the holes transporting layer. The morphology of the thin films with and without buffer layer indicates that introduction of this layer allows to obtain a homogeneous surface morphology. The results indicate that carrier injection ability and optimized charge balance is obtained to the lowest driving voltage and highest intensities efficiency among the referenced devices.

Organic solar cells using a multilayer structure MoO3/Ag/MoO3 as anode

Abstract MoO3/Ag/MoO3 structures have been grown and characterized. It is shown that the transmittance of the films increases when the silver thickness increase from 8 to 10 nm, whereas further increase induces transmittance decrease. The study of the variation of the conductivity vs. Ag thickness shows that the MoO3/Ag/MoO3 structures become highly conductive when the Ag thickness reaches 10 nm. Therefore, the optimum structure is obtained when the silver thickness is 10 nm. These MoO3/Ag/MoO3 structures have been used as anode in glass/anode/CuPc (35 nm)/C60(40 nm)/Alq3 (9 nm)/Al (120 nm) organic solar cells. These anodes permit achievable promising results, even if their efficiencies stay slightly smaller than that achieved with ITO based devices.