Ternary Blend Solar Cells Based on a Conjugated Polymer With Diketopyrrolopyrrole and Carbazole Units

Yanbin Wang,Ryo Iriguchi,Biaobing Wang,Hideo Ohkita,Jinxing Chen,Hyung Do Kim

doi:10.3389/fenrg.2018.00113

Yanbin Wang, Ryo Iriguchi + Show 4 more

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https://doi.org/10.3389/fenrg.2018.00113

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Abstract

Herein, we have synthesized a low-bandgap polymer (PCDPP4T) consisting of diketopyrrolopyrrole (DPP) and carbazole (Cz) units in the main chain. The absorption coefficient is as high as 1.3 ×10^5 cm−1 for PCDPP4T, which is slightly higher than 1.0 × 10^5 cm−1 for the monomer model compound (DPP4T-Cz). For ternary blend solar cells based on poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and only 3.4 wt% of PCDPP4T, the photocurrent increased and thus the power conversion efficiency (PCE) was improved by 30% compared to those of P3HT/PCBM binary reference cells. The improved photocurrent was ascribed partly to complementary absorption of PCDPP4T in the near-infrared (near-IR) region, and partly to efficient long-range energy transfer from P3HT to PCDPP4T, which can collect P3HT excitons that would be lost in large P3HT domains. We also discuss the origin for the improved photocurrent and requirements for further improvements.

Highlights

We synthesized a low-bandgap polymer, poly[N9′-ethylhexyl-2,7-carbazole-alt-3,6-bis(bithiophen-5-yl)-2,5 -diethylhexyl-2,5-dihydropyrrolo[3,4-]pyrrole-1,4-dione] (PCDPP4T). This polymer is based on diketopyrrolopyrrole (DPP) and carbazole (Cz) units, which are the same structure as the small conjugated molecule we reported previously: 3,6bis{5′-(9-(2-ethylhexyl)-9H-carbazol-2-yl)-[2,2′-bithiophen]-5yl}-2,5-bis(2-ethylhexyl)-pyrrolo[3,4-c]pyrole-1,4-dione (DPP4T-Cz) (Wang et al, 2018b)
The efficiency of ternary blend solar cells based on P3HT, phenyl-C61-butyric acid methyl ester (PCBM), and PCDPP4T was increased by 30% compared with P3HT/PCBM binary blend devices
The phase transition characteristics of PCDPP4T was measured by differential scanning calorimetry (DSC)

Summary

Introduction

Polymer solar cells based on donor and acceptor binary blends have been widely studied in the past three decades (Halls et al, 1995; Yu et al, 1995; Shaheen et al, 2001; Padinger et al, 2003; Li et al, 2005, 2016; Kim et al, 2006; Peet et al, 2007; Liang et al, 2010; Dou et al, 2011; Liu et al, 2014; Vohra et al, 2015; Bin et al, 2016). Ternary blend polymer solar cells exhibit improved photocurrent generation compared to binary blend counterparts. In some ternary blend polymer solar cells, the photocurrent is improved by the efficient energy transfer (Honda et al, 2009, 2010, 2011a; Xu et al, 2013; Lu et al, 2015a; Wang et al, 2015a, 2018a; Yang et al, 2017; Zhao F. et al, 2017).

Results

Conclusion