# Side chain-property relationship in LBG polymers for organic photovoltaics

Alberto Gregori, Dargie Deribew, Simon A Dowland, Isabel Fraga Domínguez, Graham Morse, Agnès Rivaton, Michael Salvador, Andres Osvet, Hans-Joachim Egelhaaf, Christoph J Brabec, et al.

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## ► To cite this version:

Alberto Gregori, Dargie Deribew, Simon A Dowland, Isabel Fraga Domínguez, Graham Morse, et al. "Side chain-property relationship in LBG polymers for organic photovoltaics. The 12th International Symposium on Functional pi-Electron Systems (Fpi-12), Jul 2015, Seattle, United States." [hal-05328061]

HAL Id: hal-05328061

https://hal.science/hal-05328061v1

Submitted on 23 Oct 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Alberto Gregori¹,², Dargie Deribew², Simon A. Dowland², Isabel Fraga Domínguez⁴,⁵, Graham Morse³, Agnès Rivaton⁴,⁵, Michael Salvador⁶,⁷, Andres Osvet⁶, Hans-Joachim Egelhaaf⁷, Christoph J. Brabec⁶,⁷, Ahmed Allal¹, Roger C. Hiorns⁸, Andreas Distler², Christine Dagron-Lartigau¹*

1. IPREM /EPCP, Université de Pau et des Pays de l'Adour (UPPA), Pau, France

2. Belectric OPV GmbH, Nuremberg, Germany

3. Merck Chemicals Ltd., Southampton, United Kingdom

4. Université Blaise Pascal, ICCF, Équipe Photochimie, Clermont-Ferrand, France

5. CNRS, UMR 6296, ICCF, Équipe Photochimie, Aubière, France

6. I-MEET, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany

7. Bavarian Center for Applied Energy Research (ZAE Bayern), Erlangen, Germany

8. CNRS, IPREM /EPCP, CNRS-UMR 5254, Pau, France

E-mail: christine.dagron-lartigau@univ-pau.fr

## Synthesis

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## Thermal properties

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<figure><img src="image_5.png" /><figcaption>(a) Thermograms of the 3 polymers (N₂, 10°C/min) (b) Differential scanning calorimetry of PSBDPP_C12 (2° cycle at 2°C/min)</figcaption></figure>

## Electronic properties

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<table><thead><tr><th>Polymer</th><th>E<sub>HOMO</sub> (eV)</th><th>E<sub>LUMO</sub> (eV)<sup>2</sup></th><th>E<sub>g</sub> (eV)</th></tr></thead><tbody><tr><td>PSBDPP_C12</td><td>-5.3</td><td>-3.9</td><td>1.4</td></tr><tr><td>PSBDPP_C16</td><td>-5.3</td><td>-3.9</td><td>1.4</td></tr><tr><td>PSBDPP_C10C6</td><td>-5.4</td><td>-3.9</td><td>1.5</td></tr></tbody></table>

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<figure><img src="image_8.png" /><figcaption>Fig X – Cyclic voltammograms of PSBDPP_C12 (a), PSBDPP_C16 (b), PSBDPP_C10C6 (c)</figcaption></figure>

## Reference

1. Zhou, E.; Yamakawa, S.; Tajima, K.; Yang, C.; Hashimoto, K. Chem. Mater. **2009**, 21, 4055;

2. Cardona, C.M.; Li, W.; Kaifer, A.E.; Stockdale, D.; Bazan, G.C. Adv. Mater. **2011**, 23, 2367–2371

## Molecular weight and dispersity

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<table><thead><tr><th>Polymer</th><th>Mn (kg/mol)</th><th>Mw (kg/mol)</th><th>D</th></tr></thead><tbody><tr><td>PSBDPP_C12</td><td>19.1</td><td>100</td><td>5.2</td></tr><tr><td>PSBDPP_C16</td><td>21.9</td><td>76.9</td><td>3.5</td></tr><tr><td>PSBDPP_C10C6</td><td>31.5</td><td>125.3</td><td>4.0</td></tr></tbody></table>

GPC traces of PSBDPP series in Chlorobenzene at 50°C against Polystyrene

## Optical properties

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<figure><img src="image_11.png" /><figcaption>(a) Normalized Absorbance of polymers in o-xylene solution and films and (b) Normalized Absorbance and Photoluminescence of films</figcaption></figure>

<table><thead><tr><th>Sample</th><th>λ<sub>Max</sub> Abs. Sol. (nm)</th><th>λ<sub>Max</sub> Abs. Film (nm)</th><th>PL Max (nm)</th><th>E<sub>g</sub> opt (eV)*</th></tr></thead><tbody><tr><td>PSBDPP_C12</td><td>781</td><td>758</td><td>1145</td><td>1.31</td></tr><tr><td>PSBDPP_C16</td><td>781</td><td>762</td><td>1100</td><td>1.37</td></tr><tr><td>PSBDPP_C10C6</td><td>788</td><td>806</td><td>1050</td><td>1.38</td></tr></tbody></table>

$$ * E_{g}^{\text{opt}} (\text{eV}) = 1240 / \lambda_{\text{cut-off}} $$

## Devices characterization

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<table><thead><tr><th>Polymer</th><th>J<sub>SC</sub> (mA/cm<sup>2</sup>)</th><th>V<sub>OC</sub> (V)</th><th>FF</th><th>PCE (%)</th></tr></thead><tbody><tr><td>PSBDPP_C12</td><td>1,89±0.10</td><td>0.50±0.01</td><td>0.44±0.01</td><td>0.42±0.02</td></tr><tr><td>PSBDPP_C16</td><td>0.60±0.09</td><td>0.46±0.02</td><td>0.34±0.03</td><td>0.10±0.02</td></tr><tr><td>PSBDPP_C10C6</td><td>0.55±0.04</td><td>0.39±0.04</td><td>0.30±0.01</td><td>0.07±0.01</td></tr></tbody></table>

Fig X – J-V curves of inverted devices (glass/ITO/ZnO/Pol:PCBM (1:2 w/w)/PEDOT:PSS/Ag) (a) and EQE Vs absorption characteristic for PSBDPP_C12 (b)

## Conclusion

* GPC shows that a branched side chain permit higher molecular weights to be obtained with respect to linear chains;

* UV-vis absorptions vary for linear and branched side chains: in the case of linear chains the main vibronic peak is gaussian while for the branched there is a shoulder at higher energies;

* PL intensity is stronger for longer and branched side chains;

* TGA shows that in all cases the alkyl-chains on both units are completely removed in one step. In the case of the branched chain (2-hexyldecyl) the degradation occurs at higher temperatures;

* DSC shows a Tg at 40°C and a reduced crystallization at 230°C for PSBDPP_C12 and similar behaviour for the others

* From the CV we can see that for linear side chains there is little influence on electronic levels, while the branched chains reduce the HOMOs;

* However, the cell parameters show reduced photocurrents from long and branched side-chain polymers that affect the overall device performance;

* This is confirmed by the EQE that shows a small photocurrent contribution from the polymers in the region 400 to ca 700 nm.

## Acknowledgements

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2011 under grant agreement ESTABLIS n° 290022)

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