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

Massimiliano Lanzi,Martina Marinelli,Elisabetta Salatelli,Filippo Pierini,Yasamin Ziai,Debora Quadretti

doi:10.3390/polym13101640

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.

Highlights

Conjugated polymer-based organic photovoltaic (OPV) solar cells are devices that can convert sunlight into electrical power via a multistep process: the generation of charged carriers upon light absorption, subsequent separation, transport, and collection to the respective electrodes [1]
2,5-dibromo-3-(6-bromohexyl)thiophene (2,5-BT6Br) [5,20] (p. 2,3); while the post-polymerization functionalization of PT6Br gave the corresponding water-soluble homopolymer PT6buP+, the water-soluble electron acceptor fullerene derivative (C603-Ser) of 19 was obtained from the properly functionalized serinol, according to the procedure shown in Scheme 1
PT6buP+, the water-soluble electron acceptor fullerene derivative (C60 -Ser) was obtained from the properly functionalized serinol, according to the procedure shown in Scheme 1

Summary

Introduction

Conjugated polymer-based organic photovoltaic (OPV) solar cells are devices that can convert sunlight into electrical power via a multistep process: the generation of charged carriers upon light absorption, subsequent separation, transport, and collection to the respective electrodes [1]. Among the different types of OPV cells, i.e., single layer and multilayer, the bulkheterojunction (BHJ) cells are undoubtedly the most attractive due to their ability to combine high efficiency with easy preparation [3]. The obtained heterojunction provides a high interface area between the two components, while promoting an efficient generation and transport of free-charge carriers. The phase separation that usually occurs with this type of system does not permit an ideal transport of charges and affects the blend morphology and its thermal stability, resulting in an important efficiency-limiting factor. The commonly reduced miscibility of the two components is an essential factor to be taken into account

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