Efficient ternary bulk heterojunction solar cells with PCDTBT as hole-cascade material

Abstract

Ternary bulk hetero-junction (BHJ) architecture for organic solar cells has been developed to enhance the power conversion efficiency (PCE) by expanding the light absorption range and smoothing the energy level at the BHJ interface. In this work, we report on a ternary polymer blend solar cell with two donor materials, polythieno[3,4-b]-thiophene/benzodithiophene (PTB7), poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT), and using C71-butyric acid methyl ester (PC71BM) as acceptor material. The resultant device shows an optimized PCE of 7.81% (control sample, 7.06%), with an open circuit voltage (Voc) of 0.76V, a short circuit current (Jsc) of 15.4mA/cm2 and a fill factor (FF) of 66.7%. The improved device performance is mainly attributed to the enhanced charge separation, improved hole mobility, and better film morphology. And we find that the third component PCDTBT can reduce charge recombination in the ternary blend system as well. The results bring new insight into the future development of high efficiency ternary organic solar cells.