Porphycene-Diketopyrrolopyrrole Conjugates As p-Type Organic Solar Cell Materials

Porphycene is a constitutional isomer of porphyrin. Porphycene has a lower LUMO level and smaller HOMO-LUMO difference than porphyrin since its molecular symmetry is lower than that of porphyrin.¹ These properties have allowed us to explore the possible applications of porphycenes in the fields of photodynamic therapy (PDT), photoinactivation of viruses and bacteria, protein mimicry, nonlinear optics, and catalysis. Recently, we have focused on the porphycene using as the semiconducting materials for organic solar cell (OSC). OSC materials require for the absorption covering the visible to NIR regions and appropriate HOMO and LUMO energy levels. In this presentation, we have designed, synthesized and properties of the porphycene–diketopyrropyrrole conjugate (Pc–DPP) though ethynyl linkages for the OSC as p-type materials. The absorption of the DPP unit appears at around 450-550 nm, while porphycene has an absorption valley around 400-550 nm. The combination of DPP and porphycene via ethynyl linkages is expected to generate absorption covering the visible to NIR regions of the spectrum. We have measured absorption spectra of Pc–­DPP and 2,7,12,17-tetrahexylporphycene (THPc) as reference compound in thin-film on glass substrate. THPc has strong Soret band at 400 nm and Q-bands around 550 to 700 nm. On the other hand, as the result of the connection with porphycene and DPP units, Pc–DPP has broad absorption covering the visible to near in-fared regions.  Based on these optical characters, we have fabricated bulk heterojunction (BHJ) OSC by solution process with Pc–DPP as a p-type material and PC₆₁BM as an n-type material. The active layer of the mixture of Pc–DPP and PC₆₁BM with 0.1% 1,8-diiodooctane containing chloroform was deposited on the PEDOT:PSS-treated ITO substrate by spin coating and then calcium and aluminum electrode were deposited on the active layer by vacuum process. After optimized the device conditions, we achieved the PCEs of 1.4% (J_sc = 4.88 mA cm^-2, V_oc = 0.81 V and FF = 0.37). We will also report the evaluations of film structures of these devices by AFM and XRD measurements.