Polymer solar cell based on ternary active layer consists of medium bandgap polymer and two non-fullerene acceptors

An efficient PSCs consisting of a ternary active layer containing a medium bandgap conjugated polymer P and two well-known non-fullerene acceptors i.e. ITIC-m and Y6 was fabricated. An overall Power Conversion Efficiency (PCE) of about 15.13% was achieved, with the optimized ternary active layer consisting of 20 wt% of ITIC-m in acceptors i.e. P:ITIC-m:Y6 (1:0.3:1.2). This value is higher than that for the binary counter parts i.e. 12.10% and 13.16% for P:ITIC-m (1:1.5 w:w) and P:Y6 (1:1.5 w:w). The higher short circuit current density of the ternary active layer PSCs is related to the broader absorption spectra as compared to the binary active layer analogs. The open circuit voltage of this ternary active layer-based PSC is in between the PSCs based on P:ITIC-m and P:Y6, which may be related with the Lowest Unoccupied Molecular Orbital (LUMO) energy levels of both the acceptor and which form the alloy between the two acceptors. The overlapping of the absorption band of Y6 with the photoluminescence of ITIC-m confirm the energy transfer from ITIC-m to Y6, leading to the improvement in short circuit current. The balanced charge transport, the reduced charge recombination and the fast charge extraction in the ternary blend lead to the higher value of FF. Thus, all these combined effects lead to the high value of PCE.