Highlighting the possibility of parallel mechanism in planar ternary photovoltaic cells

L Cattin,N Stephant,L Arzel,F Martinez,A Khelil,J C Bernède,G Neculqueo,M B Siad,M Addou,M Mastropasqua Talamo,M Morsli,P Blanchard,A Mohammed Krarroubi,Z El Jouad

doi:10.1063/1.5037531

Abstract

Ternary and binary planar heterojunctions (PHJs) have been realized and characterized. The outer layers of the active organic layers are pentathiophene (5T) and fullerene (C60), while the intercalated layer is AlPcCl. The binary, 5T/C60, 5T/AlPcCl and ternary 5T/AlPcCl/C60 PHJs were characterized by J-V and EQE measurements. The morphology of the organic layers was studied by scanning electron microscopy and atomic force microscopy, while the band structure of 5T was estimated by cyclic voltammetry. The study shows that it is possible to overcome the difficulties linked to the need for the good band matching of the three successive organic layers by using as a first electron donor layer, a layer whose morphology allows the ternary structure to behave as it was two diodes in parallel. Actually, due to this specific morphology the intercalated layer is discontinuous, which allows achieving parallel mechanism in planar ternary photovoltaic cells. This parallel mechanism in the 5T/AlPcCl/C60 organic photovoltaic cells (OPVCs) allows achieving efficiency of 1.25%, which represents a 65 % increase by comparison with the best binary 5T/C60 OPVC. It means that the morphology of the 5T layer, with its many protrusions and holes, allows ternary OPVCs to behave like parallel-linkage diodes. This behaviour allows the ternary OPVCs to achieve efficiencies higher than those obtained with the binary 5T/C60 OPVCs.

Highlights

In the field of solar cells, Organic Photovoltaic Cells (OPVCs) can become complementary to those in silicon due to their advantage of lightweight, flexibility and material diversity.[1]
We have shown in an earlier publication,[11] that the best PV performance obtained with the binary OPVC based on the couple 5T/C60 was Power conversion efficiency (PCE) = 0.81%, with Voc = 0.40 V, Jsc = 3.64 mA/cm[2] and FF = 56%, the thickness of the 5T layer being 70 nm
Through the study of ternary OPVCs we show that if the band structure is decisive, the morphology of the organic layers is critical

Summary

Introduction

In the field of solar cells, Organic Photovoltaic Cells (OPVCs) can become complementary to those in silicon due to their advantage of lightweight, flexibility and material diversity.[1] The active layer of OPVCs consists in an organic couple electron donor/electron acceptor (ED/EA) either in. Films thickness (nm) AlPcCl Voc (V) Jsc (mA/cm2) FF (%) 38 39 37.5 η (%). 0.42 0.46 0.36 the form of bulk heterojunction (BHJ) or planar heterojunction (PHJ).[2] Power conversion efficiency (PCE) of OPVCs is continuously improved through the synthesis of new ED3 and, during the last years, new EA.[4,5]

Results

Discussion

Conclusion