The Parallel Diode and Trap Behaviour of Ternary Polymer Solar Cells

This paper investigates the use of ternary blends (two donor polymers and fullerene acceptor) in bulk-heterojunction (BHJ) photovoltaic devices to compare the parallel diode and trap model. Our initial study involved the blending of equivalent quantities of two of the three chosen complimentary donor polymers (red, green, blue) with [60]PCBM. Through EQE measurements, it was shown that even devices with blends exhibiting poor efficiencies, caused by traps, both polymers contributed to the PV effect. However, traps were avoided to create a parallel-like BHJ when two polymers were chosen with the appropriate HOMO-HOMO energy band alignment. Ternary blend device performance is explained in terms of transport properties issued from photogenerated current vs. light intensity and bias polarization studies, as well as a dark conductivity vs. temperature investigation. Additionally, the parallel diode circuit model is implemented to calculate the blend combination which exhibits the highest power conversion efficiency. Device optimization issued from both models is compared