Influence of the Active Layer Structure on the Photovoltaic Performance of Water-Soluble Polythiophene-Based Solar Cells

Abstract

A new side-chain C60-fullerene functionalized thiophene copolymer bearing tributylphosphine-substituted hexylic lateral groups was successfully synthesized by means of a fast and effective post-polymerization reaction on a regioregular ω-alkylbrominated polymeric precursor. The growth of the polymeric intermediate was followed by NMR spectrometry in order to determine the most convenient reaction time. The obtained copolymer was soluble in water and polar solvents and was used as a photoactive layer in single-material organic photovoltaic (OPV) solar cells. The copolymer photovoltaic efficiency was compared with that of an OPV cell containing a water-soluble polythiophenic homopolymer, functionalized with the same tributylphosphine-substituted hexylic side chains, in a blend with a water-soluble C60-fullerene derivative. The use of a water-soluble double-cable copolymer made it possible to enhance the control on the nanomorphology of the active blend, thus reducing phase-segregation phenomena, as well as the macroscale separation between the electron acceptor and donor components. Indeed, the power conversion efficiency of OPV cells based on a single material was higher than that obtained with the classical architecture, involving the presence of two distinct ED and EA materials (PCE: 3.11% vs. 2.29%, respectively). Moreover, the synthetic procedure adopted to obtain single material-based cells is more straightforward and easier than that used for the preparation of the homopolymer-based BHJ solar cell, thus making it possible to completely avoid the long synthetic pathway which is required to prepare water-soluble fullerene derivatives.

Ionic Push–Pull Polythiophenes: A Further Step towards Eco-Friendly BHJ Organic Solar Cells

“…Indeed, by mixing the ionic push–pull polymers with ionic PT6buP , used as ionic electron donor material, a less strong but even more clear tendency of this class of materials to act as EA derivatives is displayed, representing a promising and interesting alternative solution to the use of fullerene derivatives in BHJ devices. Moreover, despite quite reduced PCE values being obtained compared to the photovoltaic performances of the former polymers/ C 60 -Ser blends, comparable values to 2.29% as PCE of the PT6buP/C 60 -Ser blend previously reported in the literature [ 33 ] are given, as PCE values ranging between 1.71–1.93% were produced ( Table 4 ). Similarly to serinol-fullerene blends, the EQE profiles of the cells ( Figure 4 d) follow the trend observed in the UV–Vis spectra of ionic polymers in thin film, indicating that the whole absorption can effectively contribute to the photocurrent, especially in the case of P2b , which also give the best photovoltaic performance.…”

“…The synthesis and characterization of poly{3-[6-(tributylphosphonium)-hexyl]-thiophene-2,5-diyl bromide} ( PT6buP ) and malonodiserinolamide fullerene ( C 60 -Ser ) as ionic ED and EA BHJ blend counterparts, respectively, were previously reported [ 33 ]. The ionic push–pull polythiophene-based materials, characterized by D-A or D-A-D sequence and based on conjugated 3-(6-bromohexyl)thiophene (ED) and benzothiadiazole (EA) moieties as building blocks, were obtained through a stepwise procedure involving the synthesis of non-ionic polymeric precursors P1 and P2 , prepared, respectively, by MW-assisted Suzuki cross-coupling polymerization [ 34 ] or oxidative coupling with FeCl 3 [ 24 ] of monomers 1 and 2 ( Scheme 2 ).…”

“…Moreover, the LUMO energy level of C 60 -Ser is close to that of PCBM (−3.91 eV) [ 47 ], whereas the HOMO of PT6buP is very close to that of P3HT (−4.76 eV) in agreement with the expected non-interaction of the ionic groups at the end of the side chain with the electronic setup of the conjugated polymer even in the solid state. The LUMO energy level of PT6buP could be established by its optical band gap ( , 2.16 eV) [ 33 ], determined by the onset absorption wavelength in thin film of the material. Indeed, through the relation HOMO + , the LUMO energy level of PT6buP is therefore −2.62 eV.…”

Strategies for the synthesis of water-soluble conjugated polymers

“…Oxygen-, sulfur-, and nitrogen-based nucleophiles are all suitable options to achieve such a modification, as demonstrated by Shida and colleagues [63]. With this method, positively or negatively charged groups can be added on the polymer structure, thus leading to a water-soluble material [64][65][66].…”

1,4-Bis((9H-Carbazol-9-yl)Methyl)Benzene-Containing Electrochromic Polymers as Potential Electrodes for High-Contrast Electrochromic Devices

“…π–conjugated polymers have recently attracted an increasing interest due to their superior benefits such as their ease of solution processing, rapid switching speeds, high coloration efficiency, and rich color palette during usage for electrochromic devices. π–conjugated polymers have a wide range of optical and electrochemical applications in field-effect transistors [ 6 , 7 ], capacitors [ 8 , 9 ], photovoltaic cells [ 10 , 11 ], light-emitting diodes [ 12 , 13 ], catalyst supports [ 14 , 15 ], and sensors [ 16 , 17 ].…”