Highly Efficient (15.08%) All-Small-Molecule Ternary Solar Cells Constructed with a Porphyrin as a Donor and Two Acceptors

A bis-porphyrin compound (VC7) has been used as a donor along with two acceptors, namely, PC71BM and IT-4F (non-fullerene), for the production of efficient all-small-molecule ternary organic solar cells (OSCs), and their performance has been compared with that of the binary counterparts. After optimization of the ternary blend VC7:PC71BM:IT-4F (1:0.3:0.9), organic solar cells showed an overall power conversion efficiency (PCE) of 15.08% (JSC = 23.74 mA/cm2, VOC = 0.87 V, and FF = 0.73), which is higher than the values obtained for the binary counterparts, i.e., 9.39 and 11.61% (JSC = 21.94 mA/cm2, VOC = 0.84 V, and FF = 0.63) for VC7:PC71BM and VC7:IT-4F, respectively. The improvement in the PCE for the ternary OSC is a consequence of the increase in the three parameters, VOC, JSC, and FF. The growth in the VOC value is associated with the upshifted LUMO level of PC71BM as compared to IT-4F. The increase in the JSC value is attributed to the higher exciton generation rate, which is associated with the effective utilization of excitons due to the broader absorption profile and energy transfer between the two acceptors (PC71BM to IT-4F). The higher FF value of the ternary OSCs is related to the more balanced charge transport and the reduced bimolecular and trap-assisted recombination, as evidenced by the increased charge carrier lifetime and low charge extraction time.