Synthesis and Characterization of Diketopyrrolopyrrole‐based D‐π‐A‐π‐D Small Molecules for Organic Solar Cell Applications

Abstract

Four new small molecules – CTDP, BCTDP, CFDP, and BCFDP having D‐π‐A‐π‐D molecular architecture, possessing carbazole and benzocarbazole as electron donors, diketopyrrolopyrrole core as acceptor and thiophene/furan acting as spacer/bridge between donor (carbazole and benzocarbazole) and acceptor (diketopyrrolopyrrole) units are synthesized. All the four compounds exhibited absorption in the range of 300 to 700 nm, and, in particular, more intense absorption found in the 500 to 660 nm region. The estimated band gaps are found to be 1.92 eV for CTDP, 1.92 eV for BCTDP, 1.94 eV for CFDP, and 1.92 eV for BCFDP from their intersection point of absorption and emission spectra. The electrochemical studies revealed that the highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels of all the four compounds, CTDP (−5.03/−3.65 eV), BCTDP (−5.03/−3.65 eV), CFDP (−4.94/−3.65 eV), and BCFDP (−4.90/−3.62 eV) are well matched with PCBM and expected to be act as donor materials in small molecule bulk hetero junction organic solar cells. All the compounds are thermally stable up to 382–416°C.