Enhanced Performance in Bulk Heterojunction Polymer Solar Cell Using Water Soluble Conjugated Polymer

Abstract

We have synthesized water-soluble polymer, poly[(9,9-bis((6'-(N,N,N-trimethylammonium)hexyl)-2,7-fluorene))-alt-bisphenylfumaronitrile]dibromide (AHF-alt-PFN), the polymer typically obtained by the Suzuki type of polymerization reaction and shows good solubility in methanol. Bulk heterojunction polymer solar cells (BHJ-PSCs) fabricated by using water soluble conjugated polymer and positive (Cs+) and negative (F-, CO2-(3)) charge ions doping as an interfacial layer for poly(3-hexylthiophene):phenyl-C61 butyric acid methyl ester (P3HT:PCBM). We have achieved an enhancement of the short circuit density and power conversion efficiency in solar cell by introducing poly(AHF-alt-PFN) layer between the active layer and the cathode metal. The device with poly(AHF-alt-PRN) layer containing F-, CO2-(3) showed a short circuit current density more 1.3, 2.3 times higher than those of the device without poly(AHF-alt-PFN) + ion layer. We explain the better performance in solar cell with poly(AHF-alt-PFN) + ion layer was due not only to the increase of electron mobility in poly(AHF-alt-PFN) layer but also to the decrease of the electron barrier near cathode by the addition of the negative ions.

Water/Ethanol Soluble p-Type Conjugated Polymers for the Use in Organic Photovoltaics

“…Although tremendous efforts have been put into the molecular design of conjugated polymers to push up the power conversion efficiencies (PCE) of single junction OPVs up to 18% (Liu et al, 2020), harmful, halogenated solvents such as chloroform, chlorobenzene or ortho-dichlorobenzene (o-DCB) are still widely used to dissolve the high-performing active materials for processing (Wang et al, 2017;Li X. et al, 2019;Fan et al, 2020). Using the materials that can only be processed with harmful solvents is undesirable for large-scale printing of OPVs due to the large quantities of solar ink required (Krebs et al, 2009(Krebs et al, , 2010, and diverges from the environmentally friendly aim of OPV (Søndergaard et al, 2011;Park et al, 2015). Recent research activities have studied more environmentally benign solvents such as anisole (Venkatesan et al, 2014), o-xylene (Xu et al, 2017;Yu et al, 2017), 2-methyl-tetrahydrofuran (Me-THF) (Fan et al, 2017;Li et al, 2018) and cyclopentyl methyl ether (Li Z. et al, 2019) for OPV manufacturing, achieving comparable or even better device performance to the OPVs fabricated using halogenated solvents.…”

“…In another approach, water/alcohol soluble conjugated polymers (WS) have been investigated as active layer materials for water/alcohol-based solar inks. Through the side-chain engineering (Huang et al, 2010;Mei and Bao, 2013;He et al, 2014;Hu et al, 2015;Park et al, 2015;Wu et al, 2016) i.e., replacing the hydrophobic aliphatic substituent with hydrophilic polar side groups, for example, ionic moieties [e.g., sulfonate groups (Mwaura et al, 2005), quaternary ammonium salt (Hu et al, 2015)] and non-ionic functional groups such as tertiary amine (Duan et al, 2013;Li et al, 2013;Lv et al, 2014;Ma et al, 2014;Cai et al, 2015) and oligoethylene glycol (OEG) (Søndergaard et al, 2011;Nguyen et al, 2017;Kim et al, 2018;Lee et al, 2018). However, the ionic moieties have been reported to act as charge carrier traps/recombination site (Yang et al, 2007;Duan et al, 2013), and the WSCPs designed based on this approach have only been successfully applied as interface layer materials for OPVs (Huang et al, 2010;Wu et al, 2016;Xu B. et al, 2016).…”