The Influence of Fluorination on Nano-Scale Phase Separation and Photovoltaic Performance of Small Molecular/PC71BM Blends.

Zhen Lu,Wanning Li,Jicheng Zhang,Wen Liu,Jingjing Li,Tao Fang,Feng Feng,Wenhua Li

doi:10.3390/nano6040080

Zhen Lu, Wanning Li + Show 6 more

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https://doi.org/10.3390/nano6040080

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Abstract

To investigate the fluorination influence on the photovoltaic performance of small molecular based organic solar cells (OSCs), six small molecules based on 2,1,3-benzothiadiazole (BT), and diketopyrrolopyrrole (DPP) as core and fluorinated phenyl (DFP) and triphenyl amine (TPA) as different terminal units (DFP-BT-DFP, DFP-BT-TPA, TPA-BT-TPA, DFP-DPP-DFP, DFP-DPP-TPA, and TPA-DPP-TPA) were synthesized. With one or two fluorinated phenyl as the end group(s), HOMO level of BT and DPP based small molecular donors were gradually decreased, inducing high open circuit voltage for fluorinated phenyl based OSCs. DFP-BT-TPA and DFP-DPP-TPA based blend films both displayed stronger nano-scale aggregation in comparison to TPA-BT-TPA and TPA-DPP-TPA, respectively, which would also lead to higher hole motilities in devices. Ultimately, improved power conversion efficiency (PCE) of 2.17% and 1.22% was acquired for DFP-BT-TPA and DFP-DPP-TPA based devices, respectively. These results demonstrated that the nano-scale aggregation size of small molecules in photovoltaic devices could be significantly enhanced by introducing a fluorine atom at the donor unit of small molecules, which will provide understanding about the relationship of chemical structure and nano-scale phase separation in OSCs.

Highlights

Organic solar cells (OSCs) have received great attention due to their advantages of solution processability, light weight, low cost, and flexibility [1,2,3,4]
Our results demonstrated that the nano-scale aggregation size of small demonstrated that the nano-scale aggregation size of small molecules in photovoltaic devices could molecules in photovoltaic devices could be significantly enhanced by introducing a fluorine atom at be significantly enhanced introducing fluorine atom the donor in unit small design molecules, which the donor unit of small by molecules, whicha provided usefulatinformation theoffurther of high provided useful information in the further design of high efficiency small molecular donors for efficiency small molecular donors for organic solar cells (OSCs)
Level of TPA-BT-TPA, DFP-BT-TPA, and DFP-BT-DFP was gradually decreased; similar tendency could be observed for DPP based small molecular donors, inducing high V oc for DFP based OSCs

Summary

Introduction

Organic solar cells (OSCs) have received great attention due to their advantages of solution processability, light weight, low cost, and flexibility [1,2,3,4]. Bulk-heterojunction architecture was adopted with the electron-efficient conjugated polymer or small molecule as the donor and electron-deficient fullerene derivative such as (6,6)-phenyl-C71 -butyric acid methyl ester (PC71 BM) as the acceptor [5,6,7]. In comparison to widely investigated polymeric counterparts, small molecule-based OSCs have distinct advantages of well-defined chemical structures, easy purification, and high purity without batch-to-batch variation [5,6,8,9]. Driven by the developing of high efficiency small molecular donors and the investigation of nano-scale phase separation at Nanomaterials 2016, 6, 80; doi:10.3390/nano6040080 www.mdpi.com/journal/nanomaterials. Nanomaterials 2016, 6, 80 donor/acceptor interfaces, power conversion efficiency (PCE) of nearly 10% for small molecule-based single-junction OSCs has been achieved [10,11].

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