Synthesis Of Three N-type Organic Semiconducting Materials And The Study On Their Photovoltaic Property

Organic solar cells have great potential for practical application.Currently,the efficiency of organic solar cells have rexceeded 17%,but still lower than inorganic solar cells.Compared with inorganic semiconducting materials,organic semiconducting materials have the advantage that their photovoltaic properties can be improved by tuning their chemical structures.Fullerene and it derivatives were the best organic solar cell acceptors and solar cells based on them have achieved over 11%PCE.However,their low LUMO energy level and weak light absorption limit device performance further improvement.In order to overcome the disadvantages of fullerene acceptors,many new n-type organic semiconducting materials have been designed and synthesized.This thesis focuses on the design and synthesis of new non-fullerene n-type semiconducting materials and studies the relationship between the structures and photovoltaic properties.?1?Synthesis of naphthalimide polymers with different alkyl side chains and the study on their photovoltaic propertiesSide chain engineering plays an important role in tuning polymer photovoltaic properties.Naphthalimide polymers with different alkyl side chains,P?NDIEH-TH2?and P?NDIEH-TT?,were designed and synthesized.Due to the smaller steric effect of the side chain,P?NDIEH-TT?shows stronger?-?stacking,narrower band gap and poorer solubility than N2200.P?NDIEH-TH2?has better solubility than P?NDIEH-TT?and N2200 due to these hexyl side chains of the dithiophene.But these hexyl side chains are harmful to?-?stacking of polymer,P?NDIEH-TH2?has bigger band gap and lower electron mobility.The PBDB-T:P?NDIEH-TH2?device achieved a V_OC of 0.96 V and a PCE of 2.44%.?2?Synthesis of naphthalimide polymer with p-difluorobenzene electron-donating unit and the study on its photovoltaic propertyD-A copolymerization is an efficient way to design polymers with narrow band gap.The properties of polymer could be improved by tuning the structure of the electron-donating unit or electron withdrawing unit.This thesis synthesized P?NDIOD-S2BF?by introducing p-difluorobenzence into N2200.Due to the electron donating ability of benzene is weaker than thiophene,P?NDIOD-S2BF?has lower HOMO energy level and larger band gap than N2200.Hydrogen bonding cannot completely prevent the rotation of single bond which lead to high energy loss.The PBDB-T:P?NDIOD-S2BF?device achieved a PCE of 1.08%.?3?Synthesis of star small molecular acceptors and the study on their photovoltaic propertiesStar-shaped small molecular acceptors are expected to have better performanceh than the linear ones because of the stronger absorption,higher solubility and better film-forming properties.In this thesis,three star-shaped small-molecular acceptors TPA-ID,TPA-IC and TPA-ICF were synthesized,with triphenylamine as the core.Due to the weak electron withdrawing abilty of ID,TPA-ID has big band gap and high HOMO energy level.The energy levels of TPA-ID are similar to PBDB-T and device based on TPA-ID did not work;Due to the combination of electron-rich group triphenylamine and strong electron withdrawing terminal group?IC and ICF?,TPA-IC and TPA-ICF have narrow bandgap?1.48 and 1.52 eV?,high HOMO energy levels and low LUMO energy levels that are matched well with that of donor PBDB-T.TPA-IC and TPA-ICF devices had respectively achieved PCE of 4.61%and 3.78%and the energy loss of devices were only 0.64 eV.