Synthesis And Performance Of Organic Photovoltaic Materials Based On Benzothiadiazole And Diketopyrrolopyrrole

Organic/polymeric solar cells (OSCs/PSCs) making use of clean and renewable solarenergy effectively, was regarded as one of the ways to relieve the energy crisis. The organicphotovoltaic donor materials have attracted public attention, which are important constitutein photo-active layer of photovoltaic cells. To study the relationship between the molecularstructure and photovoltaic performance, we designed and synthesized two classes of thedonor(D)-acceptor(A)-based organic photovoltaic donor materials, which contain a newclass of the Dn-A-based organic molecules based on benzothiadiazole (BT), diketo-pyrrolopyrrole (DPP) and triphenylamine (TPA), as well as another new class of D-D Apolymers pending BT or DPP in TPA as side chain. Their molecular structures wereconfirmed by1H NMR, elemental analysis and TOF-MS, respectively. Their photophysics,electrochemistry, and thermal stability were systematic characterized by UV-vis absorptionspectra, cyclic voltammetry (CV) and thermogravimetric analysis (TGA), respectively. Thebulk heterojunction (BHJ) organic solar cells using these small molecules or copolymers asthe donors and PCBM as the acceptor were made by solution process. The main researchresults are listed as follows.1. Four Dn-A organic small molecules used as photovoltaic donor materials (DPP-TPA,DPP-3TPA, BT-TPA and BT-3TPA) were prepared with the DPP or BT as acceptor unitsand TPA as donor unit, respectively. The influence of acceptor and number of donor in smallmolecules on photovoltaic performance in OSCs was investigated. Under the simulatedsunlight illumination of AM1.5,100mW/cm~2, the solution-processed BHJ-OSCs based onBT-3TPA showed the best device performance. The highest power conversion efficiency(PCE) of1.34%was observed with a short-circuit current (Jsc) of4.89mA/cm~2and anopen-circuit voltage (Voc) of0.82V.2. Two D-D A triphenylamine-alt-benzodithiophene copolymers of P1and P2, as well astwo D-D A triphenylamine-alt-indenofluorene copolymers of P3and P4were synthesizedwith the pending BT or DPP units as side chain. The photovoltaic performance of their BHJ-PSCs showed that the P3-and P4-based devices exhibited a higher Vocand a lower PCE thanthe P1-and P2-based devices. The P2and P4copolymers with a DPP side chain have goodfilm-forming property and broader absorption spectra. The P2-and P4-based cells presentedhigher Jsclevels. Under the simulated sunlight illumination of AM1.5,100mW/cm~2, thesolution-processed BHJ-OSCs using P1as donor showed the best device performance. Thehighest PCE of2.36%was observed with a Jscof7.12mA/cm~2and a Vocof0.84V.