Tetrathienodibenzocarbazole Based Donor-Acceptor Type Wide Band-Gap Copolymers for Polymer Solar Cell Applications

Two new donoracceptor alternating wide band gap copolymers, PTTDBC-PhQC8 and PTTDBC-BTC12, based on an electron-rich tetrathienodibenzocarbazole (TTDBC) donor have been designed and synthesized, wherein two additional thienyl rings are fused into a 2,7-dithienylcarbazole skeleton to reinforce the structural coplanarity and rigidity of polymers. The quinoid thiophene in TTDBC can endow not only a wide optical band gap (similar to 1.9 eV) but also a deep HOMO (similar to 5.3 eV) for the resulting polymers. The conventional configuration solar cells based on PTTDBC-BTC12 exhibit a large V-oc of 0.91 V and a power conversion efficiency of 4.30% (with a Jsc of 9.27 mA cm2 and a FF of 0.51), while a slightly higher PCE of 4.50% can be achieved for the inverted structure devices. We believe that these wide band gap polymers have potential to be used for tandem cell applications.