Diketopyrrolopyrrole-based Small Molecules with Simple Structure for High VOC Organic Photovoltaics

Abstract

In developing new conjugated organic materials for BHJ solar cells, a well-known architecture, alternatively composed of weak electron-donating and strong electron-accepting units, has been utilized to manipulate their electronic properties for high V oc. In this study, we have postulated that the introduction of electron-donating units with different aromatic resonance stabilization energy into the A-D-A type small molecule (SM), where A is thiophene-capped diketoppyrolopyrrole (TDPP) and D is an electron-donating unit such as thiophene (T) and phenylene (Ph), would precisely control the HOMO energy levels of the SMs for efficient OPVs. For this approach to be realized, a series of TDPP-based SMs, (TDPPh, T(TDPPh, and Ph(TDPPh, were synthesized. As expected, the HOMO energy level of T(TDPPh ( -5.17 eV) is slightly higher than that of (TDPP)2 ( -5.19 eV) due to a strong electron-donating thiophene bridge, while the HOMO energy level of Ph(TDPP)2 (-5.28 eV) is deeper than that of (TDPP)z due to the introduction of weak electron-donating phenylene bridge between two TDPPs. Consequently, the solar cell based on Ph(TDPP)2 achieved a PCE of 4.01% with high Voc of0.93 V.