MoO 3 surface passivation of the transparent anode in organic solar cells using ultrathin films

Abstract

International audienceAn 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 (C-60)/aluminum tris(8-hydroxyquinoline) (Alq(3)). 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 coverage and a sufficient transparency of the trapezoidal barrier for the tunneling of the charge carriers. The MoO3 thin films are discontinuous, and the passivation effect is improved when the oxide thin film is covered by an ultrathin gold film. Such behavior is discussed in the light of band scheme structures after contact and of geometrical considerations

Relation between Interfacial Band‐Bending and Electronic Properties in Organic Semiconductor Pentacene

“…Metal oxides were used as buffer layer under the anodes to increase their work function (WF), and enhance hole transport across the organic/electrode interface. [11][12][13][14][15][16][17] The energy level alignment has been extensively argued in many reports; [18][19][20][21][22] several models have been proposed to understand their interfacial electronic structures. The electrostatic model based on the density of states in the organic semiconductor predicted the band-bending in organic semiconductors for different work functions.…”

Towards anode with low indium content as effective anode in organic solar cells

“…The has been used as buffer layer between the anode and the organic electron donor since it has been shown that it is very efficient in improving the hole collection and OPV cells performances [15]. It can be seen in Table 1 and Fig.…”

About the transparent electrode of the organic photovoltaic cells

“…The introduction of a thin anode buffer layer (ABL) between the ITO and the ED induces a significant improvement of the device efficiency [ 8]. For instance, we have shown that Au [ 9] and MoO x [10] allow achieving this goal, by simple vacuum deposition of an ultra -thin gold film or of a thin MoO x film when CuPc is the ED. Here, the effects of a gold or MoO x ABL onto the ITO anode are studied using ED with different HOMO.…”

“…The thicknesses were 40 nm, 9 nm and 130 nm for C 60 , BCP and Al respectively. The ABL thicknesses were 0.5 nm [9] and 3.5 nm [10] for Au and MoO 3 respectively. The thickness of the different ED layers have been optimized, they are 35 nm for CuPc, 25 nm for pentacene, 20 nm for DBP and T3PM.…”