Silicon Phthalocyanines as Acceptor Candidates in Mixed Solution/Evaporation Processed Planar Heterojunction Organic Photovoltaic Devices

Marie Faure,Benoît Lessard,Trevor Grant

doi:10.3390/coatings9030203

Abstract

Silicon phthalocyanines (SiPc) are showing promise as both ternary additives and non-fullerene acceptors in organic photovoltaics (OPVs) as a result of their ease of synthesis, chemical stability and strong absorption. In this study, bis(3,4,5-trifluorophenoxy) silicon phthalocyanine ((345F)2-SiPc)) and bis(2,4,6-trifluorophenoxy) silicon phthalocyanine ((246F)2-SiPc)) are employed as acceptors in mixed solution/evaporation planar heterojunction (PHJ) devices. The donor layer, either poly(3-hexylthiophene) (P3HT) or poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), was spin coated followed by the evaporation of the SiPc acceptor thin film. Several different donor/acceptor combinations were investigated in addition to investigations to determine the effect of film thickness on device performance. Finally, the effects of annealing, prior to SiPc deposition, after SiPc deposition, and during SiPc deposition were also investigated. The devices which performed the best were obtained using PCDTBT as the donor, with a 90 nm film of (345F)2-SiPc as the acceptor, followed by thermal annealing at 150 °C for 30 min of the entire mixed solution/evaporation device. An open-circuit voltage (Voc) of 0.88 V and a fill factor (FF) of 0.52 were achieved leading to devices that outperformed corresponding fullerene-based PHJ devices.

Highlights

Organic photovoltaics (OPVs) have been of major interest over the past years as a potentially lightweight, flexible, and semi-transparent renewable energy source
We reported the use of bis(6-azidohexanoate)silicon phthalocyanine ((HxN3 )2 -silicon MPcs (SiPc)) as the first dual function ternary additive for OPV, which improved the device stability through cross linking while simultaneously increasing the power conversion efficiencies (PCEs) by absorbing in the near IR region [49]
OPV devices devices were were fabricated fabricated by by spincoating either layer followed by the thermal evaporation spincoating either P3HT or PCDTBT onto a PEDOT:PSS layer followed by the thermal evaporation ofofbis(3,4,5-trifluorophenoxy) or bis(2,4,6-trifluorophenoxy) bis(3,4,5-trifluorophenoxy) silicon siliconphthalocyanine phthalocyanine((345F)

Summary

Introduction

Organic photovoltaics (OPVs) have been of major interest over the past years as a potentially lightweight, flexible, and semi-transparent renewable energy source. The most common OPV device configuration is a bulk heterojunction (BHJ), which is based on a random network of electron donating semiconductive polymers and electron accepting small molecules [3]. BHJ OPV devices have reached high PCEs (sometimes above 15%) when employing small band gap polymers and non-fullerene acceptors (NFAs) [7,8,9,10]. In a BHJ, the active layer is a kinetically trapped blend of acceptor and donor materials that, with time and heat, will undergo a detrimental phase separation [11,12]. The active layer blend morphology is a function of the processing conditions and will depend on factors such as shearing speed and drying time, presenting significant challenges in transitioning from lab-scale device fabrication to scale-up and commercialization. The use of a planar heterojunction (PHJ), where the donor/acceptor bilayer is Coatings 2019, 9, 203; doi:10.3390/coatings9030203 www.mdpi.com/journal/coatings

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