Thieno[3,2-b]indole (TI) Based Donor Materials For Organic Solar Cells:Design,Synthesis And Photovoltaic Properties

Organic photovoltaics(OPVs)have been a hot spot because of its low cost,good flexibility,large-area flexibility and so on.It is well known that the donor materials play an important role in improving the efficiency of the OPVs,so the study of the donor materials is meaningful.In this paper,A-D-A some small molecules and D-A conjugated polymers have been synthesized by using the rare donor unit thieno[3,2-b]indole(TI)as the central building block.And the UV spectra,electrochemistry and photovoltaic properties have also been studied,the main results of these materials are as follows:To reduce the degree of the PTITBT's confusion,the two TI units were self-coupled in different ways to get the new symmetrical donor units,then incorporating with BT to get polymers P1 and P2.The UV spectra showed that the absorptions of P1 and P2 were relatively widened and had slight redshift phenomenon.At the same time,the HOMO levels of P1 and P2 were-5.22 eV and-5.41 eV respectively,they were lower than PTITBT's.And the P1 showed a better FF of 62%,but sadly the PCEs of the P1,P2 based devices were not improved.The PCE of the P1 based device was 2.69%,that was relatively higher than P2.The polymer 2D-PTITBT was obtained by changing the PTITBT's alkyl side chain to alkoxylbenzene to broaden the absorption and increaseVoc.The results showed that the UV absorption was widened,but the gap was increased instead of reduced,that's why the Jsc of 2DPTITBT was only 3.21 m A/cm2.In fact the 2D-PTITBT's device efficiency was not improved even though its HOMO level was reduced to-5.50 eV.And the PCE of 2D-PTITBT was only 0.57% with theVoc of 0.43 V and FF of 41%.The BDT was chosen as the central building block because of its extended conjugation and planar structure,and the 3-ethylrhodanine was linked by TI derivatives to get A-D-A small moleculars SM1 and SM2.They both have a long conjugate chain and a large delimitation system.The UV spectra showed that SM1,SM2 were both having wide absorptions at 300-700 nm in the film.The HOMO levels of SM1,SM2 were-5.25 eV and-5.12 eV respectively,and band gaps were 1.55 eV and 1.45 eV respectively.And their device applications are still being explored.