On the contribution of fullerene to the current of planar heterojunction organic solar cells

L Cattin,E M El-Menyawy,Z El Jouad,M A Cherif,J C Bernède,H Ftouhi,L Arzel,M Addou,S Touihri,A El Mahlali,P Torchio

doi:10.1088/1361-6463/ab7c98

Abstract

Recently, significant progress in the field of organic photovoltaic cells was obtained by substituting new electron acceptor molecules to the fullerene, which was attributed to the fact that the fullerene absorption is quite small. Nevertheless, we demonstrate in the present work that, in the case of inverted cells, i.e. when the transparent bottom electrode is used as cathode, the contribution of fullerene to the Jsc short-circuit current of the cells, if not dominant, is not negligible; and that mainly in the short wavelength spectral range. The experimental results are confirmed by an optical simulation. Due to this significant contribution to Jsc, the light transmission of the transparent electrode towards the UV-part of the spectrum is crucial for inverse cell performances. When a transparent conductive electrode based on an alternative dielectric/metal/dielectric structure is substituted to ITO, such as ZnS/Ag/TiO2, the study allows to obtain promising results, although there is a loss of performance due to the decrease of transmission of TiO2 below 400 nm in wavelength.

Highlights

Due to their lightweight, flexibility, semi-transparency [1] organic photovoltaic cells (OPVs) are complementary to silicon cells
It was demonstrated that the open circuit voltage (Voc), the fill factor (FF) and the OPV efficiency ( ) depend on the morphology of the SubPc layer, which itself depends on its deposition rate
Taking advantage of our experience acquired with the CuPc [18] we undertaken the purification of SubPc by a series of initial deposits which aimed to optimize the efficiency of the cells

Summary

Introduction

Flexibility, semi-transparency [1] organic photovoltaic cells (OPVs) are complementary to silicon cells. It was shown that IOPVs are more stable than COPVs, the interest in studying these inverted structures, even if, at times, their performances are inferior to that of COPVs [6], but this is not sysyematically the case when the ED is SubPc [7] Whatever their geometry, IOPV or COPV, two configurations are possible for the organic layer, either bulk-heterojunction (BHJ) or planar-heterojunction (PHJ). As a matter of fact, in the present work, using SubPc/C60 as heterojunction ED/EA in PHJ-IOPVs, we show that, if the SubPc contribution to the external quantum efficiency (EQE), is dominant, that of C60 is far to be negligible This experimental result is comforted by optical simulation of the OPVs. On the other hand, it is well admitted that flexible optoelectronic is promised rapid development in the coming years [8]. We show that the transmission spectrum of the TCEs is primordial for OPVs performances

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Conclusion