Synthesis and Photovoltaics of Novel 2,3,4,5-Tetrathienylthiophene-co-poly(3-hexylthiophene-2,5-diyl) Donor Polymer for Organic Solar Cell.

Morongwa E Ramoroka,Christopher J Arendse,Kwena D Modibane,Emmanuel I Iwuoha,Vivian S John-Denk,Siyabonga B Mdluli

doi:10.3390/polym13010002

Morongwa E Ramoroka, Christopher J Arendse + Show 4 more

Open Access

https://doi.org/10.3390/polym13010002

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Journal: Polymers	Publication Date: Dec 22, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of the Western Cape, University of Limpopo

Abstract

This report focuses on the synthesis of novel 2,3,4,5-tetrathienylthiophene-co-poly(3-hexylthiophene-2,5-diyl) (TTT-co-P3HT) as a donor material for organic solar cells (OSCs). The properties of the synthesized TTT-co-P3HT were compared with those of poly(3-hexylthiophene-2,5-diyl (P3HT). The structure of TTT-co-P3HT was studied using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transform infrared spectroscopy (FTIR). It was seen that TTT-co-P3HT possessed a broader electrochemical and optical band-gap as compared to P3HT. Cyclic voltammetry (CV) was used to determine lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy gaps of TTT-co-P3HT and P3HT were found to be 2.19 and 1.97 eV, respectively. Photoluminescence revealed that TTT-co-P3HT:PC71BM have insufficient electron/hole separation and charge transfer when compared to P3HT:PC71BM. All devices were fabricated outside a glovebox. Power conversion efficiency (PCE) of 1.15% was obtained for P3HT:PC71BM device and 0.14% was obtained for TTT-co-P3HT:PC71BM device. Further studies were done on fabricated OSCs during this work using electrochemical methods. The studies revealed that the presence of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on the surface of indium tin oxide (ITO) causes a reduction in cyclic voltammogram oxidation/reduction peak current and increases the charge transfer resistance in comparison with a bare ITO. We also examined the ITO/PEDOT:PSS electrode coated with TTT-co-P3HT:PC71BM, TTT-co-P3HT:PC71BM/ZnO, P3HT:PC71BM and P3HT:PC71BM/ZnO. The study revealed that PEDOT:PSS does not completely block electrons from active layer to reach the ITO electrode.

Highlights

Organic-based solar cells (OSCs) have attained considerable attention in the last decades and have been greatly studied because of their advantageous properties such as light weight, inexpensive, attractive colors and flexibility [1,2,3,4]
The research in the OSCs field focuses on designing low energy band gap donor polymers with engineered electrochemical energy levels for better charge separation which lead to an increase in the performance of OSCs [11,12,13]
The TTT-co-P3HT:PC71BM active layer has insufficient electron/hole pair separation and charge transfer at the interface, which was confirmed by photoluminescence quenching studies

Summary

Introduction

Organic-based solar cells (OSCs) have attained considerable attention in the last decades and have been greatly studied because of their advantageous properties such as light weight, inexpensive, attractive colors and flexibility [1,2,3,4]. Seibers et al [21] reported P3HT functionalized with porphyrin as an end group for use as OSC donor material Their findings revealed that porphyrin-functionalized P3HT have similar crystallinity, improved absorption properties and better OSCs performance when compared to pristine P3HT. From the conventional device fabricated during this study, the performance of P3HT based device was better than that of TTT-co-P3HT based device due to insufficient electron/hole separation and charge transfer of TTT-co-P3HT material. In both OSCs, PEDOT:PSS was used as an interlayer between ITO and active layer.

Synthesis of TTT-co-P3HT

Characterization Techniques

Fabrication of OSCs

Results and Discussion

Optical and Electrochemical Characterization

Conclusions