Effects of Bithiophene Imide Fusion on the Device Performance of Organic Thin‐Film Transistors and All‐Polymer Solar Cells. Issue 48 (3rd November 2017) - Wang, Yingfeng
Abstract: Two new bithiophene imide (BTI)‐based n‐type polymers were synthesized. f‐BTI2‐FT based on a fused BTI dimer showed a smaller band gap, a lower LUMO, and higher crystallinity than s‐BTI2‐FT containing a BTI dimer connected through a single bond. s‐BTI2‐FT exhibited a remarkable electron mobility of 0.82 cm 2 V −1 s −1, and f‐BTI2‐FT showed a further improved mobility of 1.13 cm 2 V −1 s −1 in transistors. When blended with the polymer donor PTB7‐Th, f‐BTI2‐FT‐based all‐polymer solar cells (all‐PSCs) attained a PCE of 6.85 %, the highest value for an all‐PSC not based on naphthalene (or perylene) diimide polymer acceptors. However, s‐BTI2‐FT all‐PSCs showed nearly no photovoltaic effect. The results demonstrate that f‐BTI2‐FT is one of most promising n‐type polymers and that ring fusion offers an effective approach for designing polymers with improved electrical properties. Abstract : Best used fused : Two bithiophene imide (BTI)‐based n‐type polymer semiconductors were synthesized and characterized (see structures). Both showed substantial electron mobilities in organic thin‐film transistors; however, ring fusion of the BTI dimer drastically increased the device performance of the resulting polymer in all‐polymer solar cells, with remarkable power‐conversion efficiency up to 6.85 % and a large open‐circuit voltage of 1.04 V.