18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

The development of A-DA 'D-A type small molecule acceptors (SMAs) has promoted the rapid progress of polymer solar cells (PSCs) in recent years. The outer side chains on the terminal thiophene ring and inner side chains on nitrogen atoms of the pyrrole ring of the DA 'D fused ring play important roles in the photovoltaic performance of the SMAs. Here, we synthesized two new SMAs, 2,2'-((2Z,2 'Z)-((12,13bis(2-ethylhexyl)-3,9-bis(4-(2-ethylhexyl) thiophen-2-yl)12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2.,3.: 4',5'] thieno[2', 3': 4,5] pyrrolo[3,2-g] thieno[ 2', 3':4,5] thieno [ 3,2- b] indole- 2,10- diyl)bis(methaneylylidene))bis (5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (T2EH) and 2,2 '-((2Z,2 'Z)-((12,13-bis(2ethylhexyl)-3,9-bis(3-(2-ethylhexyl)phenyl)-12,13-dihydro- [1,2,5]thiadiazolo[3,4-e]thieno[2.,3.:4',5']thieno[2',3':4,5] pyrrolo[3,2-g]thieno[2',3':4,5]thieno[ 3,2- b]indole-2,10diyl)bis( methaneylylidene))bis( 5,6-difluoro-3-oxo-2,3dihydro-1H-indene-2,1-diylidene) (P2EH), with 2-ethylhexyl beta-substituted thienyl or phenyl as the outer side chains, respectively, to improve the photovoltaic properties of the SMAs. Compared with P2EH, T2EH exhibits closer p-p stacking, slightly red-shifted absorption, and higher electron mobility. Moreover, the active layer of T2EH blended with the low-cost polymer donor poly[(thiophene)-alt-(6,7-difluoro- 2-(2-hexyldecyloxy)quinoxaline)] (PTQ10) possesses higher mobilities, a longer lifetime, and less recombination of the charge carriers in comparison with that of the PTQ10:P2EH active layer. Eventually, the PTQ10:T2EH-based PSCs showed an outstanding power conversion efficiency (PCE) of 18.55%, while the PSC based on PTQ10:P2EH displayed a PCE of 17.50%. Importantly, 18.55% is the highest PCE in the PTQ10-based binary PSCs so far. The results indicate that T2EH is one of the best SMAs for the PTQ10-based PSCs and is a promising SMA for the application of PSCs.

Automated summary

The development of A-DA 'D-A type small molecule acceptors has greatly advanced polymer solar cell technology. By modifying the outer and inner side chains of the acceptor, the photovoltaic properties can be improved. T2EH has been identified as one of the best acceptors for PTQ10-based polymer solar cells.