|HOMO / LUMO||HOMO = -5.34 eV, LUMO = -3.69 eV |
|Solubility/processing solvents||Dichlorobenzene or Chlorobenzene+dichlorobenzene (1:1 v/v) at elevated temperature ca. 110 °C|
|Classification / Family||Benzothiadiazole, Fluorinated benzothiadiazole, Heterocyclic five-membered ring, Organic semiconducting materials, Low band gap polymers, Organic Photovoltaics, Polymer Solar Cells|
PffBT4T-2OD (PCE11) is a low band-gap (1.65 eV) semiconducting polymer for organic photovoltaics (OPVs), which has reached power conversion efficiencies (PCEs) approaching 11% . These efficiencies are a result of the high crystallinity of the polymer, providing excellent hole transport mobilities on the order of 10-2 cm2V-1s-1, and the ability to use a thick active layer, resulting in improved light absorption.
The size and position of the alkyl chains of PffBT4T-2OD are critical to its temperature dependant aggregation properties, enabling control over the aggregation and crystallisation of the polymer to produce an efficient donor:acceptor film morphology.
Polymer PCE11 was targeted by reacting 4,7-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]-thiadiazole with 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene engaging Stille Coupling reaction.
PCE11 (PffBT4T-2OD) synthesis with 4,7-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-5,6-difluorobenzo[c][1,2,5]-thiadiazole with 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene as starting materials engaging Stille Coupling reaction.
The structure of the high-performance (10 - 11%) devices was:
ITO / ZnO / PffBT4T-2OD:PC70BM (200 – 300 nm) / MoO3 or V2O5 (20 nm) / Al (100 nm)
PffBT4T-2OD:PC70BM solution details:
- Blend ratio: 1:1.2,
- Polymer concentration: 9 mg/ml,
- Solvent: 1:1 blend of chlorobenzene and dichlorobenzene,
- Additive: 3% diiodooctane,
- Heating: 85°C for dissolution,
It is important to note that this solution (and the substrate being deposited onto) must be heated for spin casting, with the ideal temperature being 60 – 80°C. It is reported that a solution and substrate pre-heating temperature of 110°C should be used to allow for cooling that will occur before deposition.
Literature and Reviews
- Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells, Y. Liu, et al., Nat. Comm., 5, 5293 (2014)
- High-efficiency non-fullerene organic solar cells enabled by a difluorobenzothiadiazole-based donor polymer combined with a properly matched small molecule acceptor, J. Zhao et al., Energy Environ. Sci., 8, 520-525 (2015)