“N‐<i>π</i>‐N” Type Oligomeric Acceptor Achieves an OPV Efficiency of 18.19% with Low Energy Loss and Excellent Stability
Lili Zhang, Ziqi Zhang, Dan Deng, Huiqiong Zhou, Jianqi Zhang, Zhixiang Wei
Abstract
Abstract A novel “N‐ π ‐N” type oligomeric acceptor of 2BTP‐2F‐T, constructed by two small non‐fullerene acceptor (NFA) units linked with a thiophene π bridge is reported. The 2BTP‐2F‐T not only combines the advantages of small NFA and polymeric acceptors (PYF‐T‐ o ) with similar units but also exhibits superior characteristics of high absorption coefficient and high electron moblity( µ e) ) with less dependence on molecular packing. Using PM6 as the donor, a remarkable efficiency of 18.19% is obtained with an open circuit ( V oc ) of 0.911 V, short current circuit ( J sc ) of 25.50 mA cm −2 , and fill factor (FF) of 78.3%, which is much better than that of the corresponding monomer (16.54%) and PYF‐T‐ o (15.8%) based devices. The much‐improved efficiency results from two aspects: 1) an enhanced FF due to the largely improved µ e and well‐controlled morphology ; 2) a higher value of ( J sc × V oc ) due to its higher absorption coefficient and efficient charge generation at a similar low energy loss. Furthermore, the PM6/2BTP‐2F‐T device possesses the longest T 80 lifetime to light‐soaking and comparable high thermal stability with PM6/PYF‐T‐ o . The results indicate that the “N‐ π ‐N” type oligomeric acceptor has a great application prospect due to its superior high efficiency and improved stability in organic solar cells.