Device Engineering On PBDB-T:N2200 Based All-Polymer Solar Cells

In recent years,the rapid development of the power conversion efficiency(PCE)of polymer-polymer(all-polymer)organic solar cells(OSCs)is mainly based on the spring up of new polymer materials.But research on the device engineering is relatively rare.Therefore,this thesis focuses on the effects of device fabrication conditions,processing techniques and device structure on the performance of all-polymer solar cell devices.The main contents of the thesis are as follows:Firstly,polymer/neat-C70 OSCs employing a series of novel narrow optical gap polymer PBDs have been successfully demonstrated with improved efficiency relative to the tranditional device based on PCBM.A best PCE of 6.1%with improved thermal stability and low cost has been achieved for such types of OSCs based on a tailored polymer PBD6.However,the fullerene material has insufficient ability to absorb sunlight in the visible light region,and the use of a polymer as an acceptor is expected to further improve the PCE of the device while ensuring good stability.Furthermore,the performance of polymer solar cells using polymers N2200 and PCBM as electron acceptors were systematically compared,respectively.In this chapter,the tolerant of moisture for different bulk heterojunction blends was first compared PCBM-based blends only maintain stable performamnce under humidity from 0%to 20%,while all-polymer blends exhibit unprecedentedly stable performance(best PCE approaching 9%)from 0%up to 80%.Next,a long-term stability characterization of unencapsulated organic solar cells was conducted.Encapsulation-free all-polymer solar cell devices exhibit excellent stability with/without thermal stress as well as aged at ambient condition(≈z25℃,relative humidity:20%).These results indicate that the all－polymer solar cell is significantly superior to the conventional polymer-fullerene solar cell in both PCE and preparation processMeanwhile,in order to further enhance the PCE of all-polymer solar cells by engineering the active layer,the effect of n-type dopants TBAX(TBAF,TBAC1,TBABr and TBAI)on the performance of all-polymer solar cells based on PBDB-T:N2200 were systematically investigated.With relatively low concentration n-doping(0.04 wt%),significantly increased fill factor(FF)and slightly increased short-circuit current density(Jsc)are observed in all cases.Expecialilly for TBAI,the PCEs increase from 5.8%to over 7.0%.The n-type molecular doping can efficiently suppress charge recombination,resulting in improved diode ideality factor,FF,and Jsc.Finally,a new device structure is explored to solve the problems of carrier recombination loss and transport bottleneck in the current all-polymer bulk heterojunction film,in order to improve the Jsc and FF of the device.An all-polymer P/N planar heterojunction prepared by low-temperature solution method have been proposed.Polymer donor(PBDB-T)and acceptor(N2200)were still used to prepare all-polymer solar cells with a highest PCE apporching 9.52%,significantly improved compared to that of 6-7%for conventional bulk heterojunction solar cells.Synergistic improvement in nearly all device parameters as well as enhanced device absorption,decreased geminate recombination and improved charge transport and collection.In summary,this thesis studied the morphology,electrical properties,stability of organic solar cells through the design and synthesis of new materials as well as device engineering(procssed conditions,doping treatment and device structure).This thesis provides new ideas and approaches to further improve the performance of organic solar cells,especially all-polymer solar cells.