A mono(carboxy)porphyrin-triazine-(bodipy)2 triad as a donor for bulk heterojunction organic solar cells

Abstract

In the present article bulk heterojunction (BHJ) solution processed organic solar cells have been prepared using a mono(carboxy)porphyrin-triazine-(bodipy)₂ triad (PorCOOH)(BDP)₂ as a donor and ([6,6]-phenyl C₇₁ butyric acid methyl ester) (PC₇₁BM) as an acceptor. This donor–acceptor system aims to increase the light capturing process efficiency of the device. The solution processed BHJ organic solar cell with an optimized weight ratio of 1 : 1 (PorCOOH)(BDP)₂ : PC₇₁BM processed with THF as a solvent showed an overall power conversion efficiency (PCE) of 3.48% with short circuit current J_sc = 8.04 mA cm⁻², open circuit voltage V_oc = 0.94 V and fill factor FF = 0.46. The relatively high value of V_oc was attributed to the deeper highest occupied molecular orbital energy level of (PorCOOH)(BDP)₂. When the active layer of the solar cell was processed using a mixture of 4% v/v of pyridine in THF solvent, it achieved a PCE value of 5.29% with J_sc = 10.48 mA cm⁻², V_oc = 0.90 V and FF = 0.56. This was ascribed to the enhancement of both the J_sc and the FF values. The higher value of J_sc is explained by the increased absorption profile of the blend, the stronger incident photon to current efficiency (IPCE) response and the higher crystallinity of the active layer, induced by the solvent additive while the enhancement of FF may be due to the better charge transport capability and the charge collection efficiency in the later device.