So-Huei Kang

Ternary solar cells with a mixed face-on and edge-on orientation enable an unprecedented efficiency of 12.1%

Ternary organic solar cells (OSCs), with a simple structure, can be easily adopted as sub-cells in a tandem design, thereby further enhancing the power conversion efficiency (PCE). Considering the potential to surpass the theoretical PCE limit in OSCs, we incorporated a benzo[1,2-b;4,5-b′]dithiophene-based small molecule into a poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl):[6,6]-phenyl-C71-butyric acid methyl ester host system. A hitherto unrealized PCE of 12.1% was achieved at the optimized composition of the ternary blend. The ternary blend surprisingly had a face-on and edge-on co-existent texture, which is far better than that of the face-on orientated host film. To the best of our knowledge, this intriguing result refutes for the first time a general paradigm that high-performance OSCs are unambiguously linked to face-on structures. Therefore, our study provides a new platform for refining the theoretical underpinning of multiple blending OSCs.

An efficient lactone-to-lactam conversion for the synthesis of thiophene Pechmann lactam and the characterization of polymers thereof

Despite having unique structural features, e.g., high co-planarity and a strong polar bicyclic lactam structure, thiophene bipyrrolylidene-2,2′(1H,1′H)-dione (TBPD) has been less explored as a dye, mainly due to the quite low yield in its synthesis via lactone-to-lactam conversion. We reported an efficient methodology for synthesizing TBPD in high yield using p-toluenesulfonic acid monohydrate and a catalytic amount of 4-dimethylaminopyridine in the chloroform solvent. From the newly synthesized series of TBPD-based donor–acceptor-type polymers, we fabricated organic field-effect transistors (OFETs), which were subjected to a systematic study on the relationship between film microstructure and charge transport. Among them, the annealed PTBPD-Th film revealed a more ordered lamellar packing with the highest number of interlayers and preferential edge-on orientation, yielding the best hole mobility (up to 0.46 cm2 V−1 s−1). The improved synthesis of TBPD and our findings concerning related polymers could promote further research and development associated with the TBPD unit.