Reducing Energy Loss in Organic Solar Cells by Changing the Central Metal in Metalloporphyrins

The effect of central donor core on the properties of A-pi-D-pi-A donors, where D is a porphyrin macrocycle, cyclopenta[2,1-b:3,4-b']dithiophene is the pi bridge, and A is a dicyanorhodanine terminal unit, was investigated for the fabrication of the organic solar cells (OSCs), along [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptor. A new molecule consisting of Ni-porphyrin central donor core (VC9) showed deep HOMO energy level and OSCs based on optimized VC9:PC71BM realized overall power conversion efficiency (PCE) of 10.66 % [short-circuit current density (J(SC))=15.48 mA/cm(2), fill factor (FF)=0.65] with high open circuit voltage (V-OC) of 1.06 V and very low energy loss of 0.49 eV, whereas the Zn-porphyrin analogue VC8:PC71BM showed PCE of 9.69 % with V-OC of 0.89 V, J(SC) of 16.25 mA/cm(2) and FF of 0.67. Although the OSCs based on VC8 showed higher J(SC) in comparison to VC9, originating from the broader absorption profile of VC8 that led to more exciton generation, the higher value of PCE of VC9 is owing to the higher V-OC and reduced energy loss.