Donor-Acceptor Copolymers Based On The Novel Donor Units: Densign,Synthesis And Investigation Of Photovoltaic Properties

Polymer Solar Cells?PSCs?have attracted an increasing amount of attention due to their potential as a low-cost clean means to convert solar energy into electricity,as well as applications in flexible,light-weight,transparent and large-area devices.the PCE of BHJ PSCs has been improved from below 1%to 12%rapidly during the past decades.Despite the development of PSC device fabrication technique,more promising candidate donor conjugated polymers are still extremely in demand.The design and synthesis of novel polymer materials has important significance for the improvement of device performance.To date,introducing the donor and the acceptor unit?D-A?in the conjugated backon is the most common and effective strategies.The main works of the thesis is to design and synthesize the D-A low bandgap conjugated polymer including the bridged or fused donor unit and apply in polymer solar cells.The completed works and the results are mainly summarized as follows:1.A facile synthetic strategy toward thieno[3,2-b]indole?TI?,structurally analogous to carbazole,was developed by the cadogan annulation method.Three donor-acceptor?D-A?conjugated polymers P1,P2 and P3 containing N-alkyl-TI as the donor unit and4,7-dithien-5-yl-2,1,3-benzodiathiazole?DTBT?as the acceptor unit were successfully synthesized and applied to BHJ?PSCs?.Different side chains were introduced to TI units?for P2?or DTBT units?for P3?,the results indicate that the bandgaps,energy levels and photovoltaic performance were finely tuned by the side chains in the TI-DTBT copolymer.PCE based on the device structure of ITO/PEDOT:PSS/polymer:PC₇₁BM/Ca/Al exhibit a large distinction?1.61%for P1,0.53%for P2 and 2.73%for P3?at the optimal device fabrication conditions.The optimized devices based on P3:PC₇₁BM blends with a relatively higher mobility(2.84×10^-5cm² V^–1s^–1)show the best PCE under air mass 1.5 global?AM 1.5 G?irradiation of100 mW cm^-2,which is in good agreement with its high current density and light absorption property.Accordingly,the TI unit can be used as the efficient donor units for D-A conjugated donor materials for PSCs application.In addition,this work suggests that the side chains on low bandgap polymers significantly impact theirproperties and the observed PCEs of the corresponding BHJ solar cells.2.Three D-A conjugated polymers?PTIBT,PTITBT and PTIDTBT?containing N-alkyl-TI as the donor units,2,1,3-benzodiathiazole?BT?as the acceptor units and none,single,double thiophene as the spacers were synthesized.The thiophene spacers show a dramatic impact on the physical and electrochemical properties of these copolymers.These polymer donors are subject to the fabrication of bulk heterojunction polymer solar cells?BHJ PSCs?.Preliminarily,PCEs based on the device structure of ITO/PEDOT:PSS/Polymer:PC₇₁BM/Ca/Al exhibit a large distinction?1.61%for PTIBT,5.83%for PTITBT and 1.79%for PTIDTBT?at the optimal device fabrication conditions.The device based on PTITBT:PC₇₁BM?1:3,w/w?shows the best PCE of 5.93%(V_OC=0.69 V,J_SC=13.92 mA cm^-2,FF=61.8%),which represents one of the best performances among PCDTBT analogues.In addition,the Jsc of 13.92 mA cm^-2is also among the highest J_SCvalues of all PCDTBT analogues.our results suggesting that incorporating thiophene unit into D-A conjugated polymers have a great influence on the property and the device performace of the materials.3.From the view of the structural isomerization,the isomer of IDT,namely iso-IDT,was designed and synthesized for the first time.The IDT and iso-IDT unit were copolymerized with DTBT acceptor by Stille polycondensation to afford the two copolymers,PIDTDTBT and Piso-IDTDTBT,respectively.By the theoretical calculation,It is found that backbone curvature of polymers were obviously different.Piso-IDTDTBT possess the stronger curvature leading to the weaker interchain interactions and the wider optical band gap,yet,PIDTDTBT with the weaker curvature showed wider and stronger absorption,the higher mobility and the better performance?5.28%?,Piso-IDTDTBT with the stronger curvature displayed lower the mobility and the device perfoemance?3.56%?,however,the deeper HOMO energy level for Piso-IDTDTBT caused the higher V_OC?about 1.0 V?.This work suggested that the structural isomerization of the donor unit leading to the different backbone curvature of polymer,which have a great influence on the absorption,energy level,mobility and the device performance.In addition,isomer chemistry could be used as an effective strategy for designing new organic semiconducting materials.4.A nonacyclic fused TIBDP unit,consisting of bridged-TI,was designed and synthesized.Two D-A copolymers PTIBDP-BT and PTIBDP-DTBT were developed in which TIBDP as the donor unit and 2,1,3-benzothiadiazole?BT?and 4,7-dithienyl-2,1,3-benzothiadiazole?DTBT?as the acceptor units by Suzuki and Stille coupling reaction,respectively.Meanwhile the thermal properties,absorption,and the electronic properties of the polymers were characterized and measured.when they applied to the organic solar cells,the devices based on the PTIBDP-BT and PTIBDP-DTBT exhibited the PCE of 4.02%and 3.72%under the thermal annealing,respectively.when they applied to the organic field effect transistor memory,PTIBDP-BT and PTIBDP-DTBT achieved a FET mobility of 1.3×10^-2cm² V^-1s^-1under DIO as the solvent additive,the I_on/offof PTIBDP-BT and PTIBDP-DTBT was 5×10³ and 1.82×10⁴,respectively.PTIBDP-BT and PTIBDP-DTBT possessed the memory window of 40 V and 86 V,This work suggesting that nonacyclic acene TIBDP as the donor unit based on TI can be used to construct the D-A polymer and applied to the polymer solar cells and OFET memory.