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Biology

Indacenodithienothiophene-Based Ternary Organic Solar Cells: Concept, Devices and Optoelectronic Analysis

Published: February 01, 2016
, , , , , , , , , ,
1Institute of Materials for Electronics and Energy Technology (I-MEET),Friedrich-Alexander-University Erlangen-Nuremberg, 2Macromolecular Chemistry Group (buwmakro) and Institute for Polymer Technology,Bergische Universität Wuppertal, 3Department of Materials Science Engineering,University of Ioannina, 4Advent Technologies SA, 5National Hellenic Research Foundation (NHRF), 6Bavarian Center for Applied Energy Research (ZAE Bayern)

Summary

In this study, in addition to the synthesis of a novel polymer, we fully characterize a ternary bulk-heterojunction solar cell, with a power conversion efficiency exceeding 4.6%, with the complementary use of optical and electrical techniques.

Abstract

We report on a novel ternary bulk-heterojunction solar cell by implementing a novel conjugated polymer (ADV-2) containing alternating pyridyl[2,1,3]thiadiazole (PT) between two different donor fragments, dithienosilole (DTS) and indacenodithienothiophene (IDTT), into a host system of indacenodithieno[3,2-b]thiophene,2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). A clear absorption contribution in the near infrared (NIR) region leads to a power conversion efficiency (PCE) exceeding 4.6% in ternary device processed by doctor blading in air, fully avoiding any thermal treatment. Current-voltage (J-V) characteristics, external quantum efficiency (EQE) spectrum, charge extraction (CE) as well as photo-induced absorption (PIA) spectroscopy reveal the higher charge carrier generation in the ternary devices compared to the reference binary cells. Despite an enhancement of about 20% in the short circuit current density (Jsc), the lower fill factor (FF) achieved in PIDTTQ:ADV-2:PC71BM ternary system limits the solar cell performance. With the complementary use of photoinduced charge carrier extraction by linearly increasing voltage (photo-CELIV) and transient photovoltage (TPV) measurements, we found that the ternary cells suffer from a lower mobility-lifetime (µτ) product, adversely impacting the FF. However, the significant improvement of light harvesting in the NIR region, compensating the transport losses, results in an overall power conversion efficiency enhancement of ~7% for ternary blends as compared to the PIDTTQ: PC71BM devices.

Introduction

During the last decades, the power conversion efficiency (PCE) of organic bulk-hetorojunction (BHJ) solar cells based on donor/acceptor blends surpassed the 10% threshold, mainly due to the discovery of novel materials as well as device structure engineering.1,2,3,4,5,6 Nowadays, one of the main challenges in order to further boost the PCE of organic solar cells is to achieve better absorption match to the solar irradiance spectrum, by extending the narrow absorption window of organic polymers. In this regards, two main concepts have been developed: tandem and ternary organic solar cells.7,8,9,10,11,12,13,14,15,16,17 The former are based on a complex multi-layer stack with the main challenge of designing a robust solution-processed intermediate layer.18 The latter, made of two donors and one acceptor, mixed together in a unique solution, overcomes the complexities of the tandem device architecture, maintaining the easy processability of a single junction organic BHJ solar cell.19,20,21,22,23,24,25 To date, polymers,20 small molecules,21 dyes,26 quantum dots27 and fullerene derivates,23 have been adopted as "guest" in the polymer-fullerene "host" system.

In addition to the need for donor materials with the complementary absorption, one of the key points to surpass the performance of binary cells in ternary devices is to find donor materials with compatible physical and chemical natures.20 This can prevent the formation of recombination centers, or morphological traps, that deteriorate the photovoltaic properties.28,29

Here, we report a ternary organic solar cell system processed in air that shows a pronounced sensitization effect, resulting in a power conversion efficiency of more than 4.6%. As a sensitizer, we incorporate the near infrared (NIR) polymer ADV-2 that contains alternating pyridyl[2,1,3]thiadiazole (PT) between two different donor fragments, dithienosilole (DTS) and indacenodithienothiophene (IDTT), into a host system of indacenodithieno[3,2-b]thiophene,2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ)30 blended with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). In fact, in order to have components with a similar chemical nature in the ternary blend system, we used two polymers with the same backbone unit of indacenodithienothiophene for the host and the guest donors. We studied the aforementioned ternary system by employing various optoelectronic techniques such as current-voltage (J-V) characteristics, external quantum efficiency (EQE), photoinduced charge carrier extraction by linearly increasing voltage (photo-CELIV), charge extraction (CE), transient photovoltage (TPV) measurements and photo-induced absorption (PIA) spectroscopy.

Protocol

1. Planning of experiment Identify two donor copolymers with complementary absorption in the visible-NIR range and with suitable energy levels in comparison with the fullerene derivative acceptor (PC71BM). 2. Synthesis of M1 Add a 10 mL freshly distilled toluene solution containing 5,5'-bis(trimethylstannyl)-3,3'-di-2-ethylhexylsilylene-2,2'-bithiophene (0.372 g, 0.5 mmol, the quantity as well as the representative mmol corresponds to 5,5&#…

Representative Results

 Figure 1 shows 1H and 13C NMR spectra of M1 (a-b, respectively) and ADV-2 (c-d, respectively) with their respectively list of peaks. Figure 2 shows the synthetic route for the low band gap donor-acceptor copolymer ADV-2. Figure 3 shows the absorption spectrum of ADV-2 in DCB solution and as solid. The copolymer for both cases shows a single band in the high energy region which is assigned to a localized π−π* transition and another a…

Discussion

We reported a novel ternary system with a clear contribution in the incident photon-to-current efficiency in the near IR region. A Jsc improvement of around 20% was obtained for PIDTTQ:ADV-2:PC71BM (0.85:0.15:2) ternary devices compared to PIDTTQ:PC71BM binary cells. However, the low FF limited the performances of the ternary BHJ solar cells.

We found that by adding ADV-2 into the host system of PIDTTQ:PC71BM the μ&#96…

Disclosures

The authors have nothing to disclose.

Acknowledgements

This project has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under the Grant Agreement n° 607585 project OSNIRO. In addition, this project has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under the Grant Agreement no. 331389. C. L. C. acknowledges the financial support of a Marie Curie Intra European Fellowship (FP7-PEOPLE-2012-IEF) project ECOCHEM. G. P. would like to thank the Ministry of Education and Religious Affairs in Greece for the financial support of this work provided under the co-operational program “AdvePol: E850″. The authors gratefully acknowledge the support of the Cluster of Excellence ”Engineering of Advanced Materials” at the University of Erlangen-Nuremberg, which is funded by the German Research Foundation (DFG) within the framework of its ”Excellence Initiative”, Synthetic Carbon Allotropes (SFB953) and Solar Technologies go Hybrid (SolTech).

Materials

1,2-Dichlorobenzene Aldrich 606078 solvent
1-Chloronaphtalene Aldrich 970836 solvent
chloroform  Aldrich 1731042 solvent
PC71BM Solenne 07099 BHJ material
Toluene Aldrich 2036259 solvent
Chloroform-d Aldrich 1697633 solvent
trichlorobenzene  Aldrich 956819 solvent
5,5’-bis(trimethylstannyl)-3,3’-di-2-ethylhexylsilylene-2,2’-bithiophene Aldrich 143367-56-0 starting material
Pd(PPh3)4  Aldrich 14221-01-3 catalyst
source measurements unit  BoTEst
Solar simulator Oriel Sol 1A Newport
Spectrometer Lambda 950 Perkin Elmer
EQE setup Enlitech
oscilloscope DSO-X 2024A Agilent Technologies 
NMR setup Bruker AVANCE III 600 
GPC setup Alliance 2000 
Doctor blade Zehntner ZAA 2300
evaporator mbraun
glove boxes mbraun
Laser 405 nm THORLABS
funtion generator Agilent Technologies 33500B series
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References

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Biologyternary organic solar cellsindacenodithienothiophenephoto-CELIVTransient PhotovoltageCharge extractionPhoto-induced absorption spectroscopy
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Gasparini, N., García-Rodríguez, A., Katsouras, A., Avgeropoulos, A., Pagona, G., Gregoriou, V. G., Chochos, C. L., Allard, S., Scherf, U., Brabec, C. J., Ameri, T. Indacenodithienothiophene-Based Ternary Organic Solar Cells: Concept, Devices and Optoelectronic Analysis. J. Vis. Exp. (Pending Publication), e54007, doi: (2016).
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