Contrastive manipulations on vertical stratifications by a fluorescent guest component in ternary nonfullerene and fullerene organic solar cells

Herein, a simple fluorescent material TPA2O (5,5'-((4'-(diphenylamino)-[1,1'-biphenyl]-2,6-diyl)bis(meth-aneylylidene))bis(1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione)) is designed and successively introduced into both polymer:nonfullerene and polymer:fullerene blends to construct ternary organic solar cells with an inverted structure of ITO/ZnO/active layer/MoO3/Ag. Remarkably improved power conversion efficiency by up to 25% (from 9.21% to 11.47%) and sufficiently enhanced photocurrent (from 21.01 to 25.25 mA cm(-2)) are realized in nonfullerene ternary devices by incorporating a small amount of TPA2O, while reduced PCE is found in ternary fullerene systems. Characterizations have proven that efficient Forster resonance energy transfer (FRET) exists between TPA2O and the host PTB7-Th donor. And the distinguishable device performance in different ternary systems is determined by the contrastive influences on lateral and longitudinal direction morphologies. Specifically, by incorporating TPA2O, the cross-section morphology is degenerated in ternary fullerene blends but stable in ternary nonfullerene blends. More interestingly, for vertical-section morphology, PTB7-Th is more enriched in the upper layers in ternary nonfullerene blends, which is close to hole-transport MoO3 and inducing more efficient hole transport. Whereas PTB7-Th is less concentrated within the top layers in ternary PC71BM-based blends. Moreover, remarkably enhanced thermal stability is observed in TPA2O-based nonfullerene devices, with 94% of the initial PCE after baking at 80 degrees C for 144 h, compared to 75% and 62% of IEICO-4F and PC71BM binary devices, respectively.

Automated summary

Here, a simple fluorescent material TPA2O is introduced into both polymer:nonfullerene and polymer:fullerene blends to construct ternary organic solar cells. The addition of TPA2O significantly improves the power conversion efficiency and photocurrent in nonfullerene systems, while reduced efficiency is found in fullerene systems. The study also reveals the influence of TPA2O on the morphology of the devices and the enhanced thermal stability in nonfullerene devices.