The Research Of Interface Engineering And Ternary Device In Organic Solar Cells

The green and renewable solar energy is the most potential replacement for traditional energy.Bulk-heterojunction organic solar cells（OSCs）have been developed rapidly due to the key properties of great potential for low cost,straightforward fabrication processes and fabrication on large area and flexible substrate.While the power conversion efficiency（PCE）and life time still need further enhancement to satisfy the demand of industrial production.So the solution of how to improve the PCE and stability of OSCs has drawn momentous attention.There are many effective ways to achieve this goal,such as development of new donor/acceptor materials,introduction of electrode interface layer,fabrication of ternary or tandem OSCs and so on.The incorporation of interfacial compatilizer materials is available to improve the thermal stability of OSCs.This thesis will focus on the developing of the cathode interface,donor-acceptor interface of binary OSCs and the fabrication of ternary OSCs.The main achievements of this research are as follows:（1）The eco-friendly n-type water/alcohol-soluble conjugated polyelectrolyte PF_EOSO₃Li was applied as a cathode interfacial layer in non-fullerene OSCs.On account of self-assembly property of conjugated polyelectrolytes,theπ-delocalized polyfluorene backbone had an intimate connection with the hydrophobic active layer,and the side chain with lithium ion may move toward the ZnO layer.The self-assembly process can promote the formation of strong interfacial dipoles between ZnO and the active layer,which dramatically lowered the work function of ZnO.Meanwhile,the surface of ZnO became more hydrophobic after coating with PF_EOSO₃Li.The introduction of lithium ions as spectator cations may contribute to reduction of the intrinsic surface defects of ZnO.So the OSCs based on ZnO/PF_EOSO₃Li as ETLs show better device performance and stability.As a result,inverted organic solar cell devices with ZnO/PF_EOSO₃Li double-ETLs exhibit high efficiencies of 11.7%and 10.6%for PBDB-T:IT-M and PBDB-T:ITIC blend systems,respectively.（2）An industrially produced conjugate electrolyte small molecule 1-pyrenemethanol（PyM）with the advantages of low cost and environmentally friendly was effectively applied to modify ZnO in non-fullerene OSCs.PyM had good solubility in both methyl alcohol and chlorobenzene.Thus,after coating the active layer,the redundant PyM was washed away,a thin PyM layer distributed on the ZnO surface because of the hydrogen bond interaction and a small amount PyM blended with bottom active layer.Then the work function and surface defects of ZnO were reduced and the device performance was enhanced.As a result,the OSCs based on ZnO/PyM（thickness of PyM ranges from several to over one hundred nanometers）all showed better performance than bare ZnO devices.Correspondingly,the best device performances using PBDB-T:ITIC and PBDB-T:IT-M as the active layer based ZnO/PyM（¹0 nm）were 10.9%and 11.5%.（3）A straight forward synthetic amination-functionalized fullerene derivative PCBDCU has been utilized as an additive in the active layer with an inverted OSCs structure ITO/Donor:Acceptor:PCBDCU/MoO₃/Al.The PCBDCU will spontaneous moves to ITO because of self-assembly properties of molecules.Then a thin layer PCBDCU formed on ITO surface and acted as electron transport layer,which contributed to the lower work function of cathode and improved the device performance.Meanwhile,a small amount of PCBM will move towards ITO because the similar chemical structure to PCBDCU.As a result,the active layer showed reasonable vertical phase separation and the device performance was enhanced.When doped with 10 wt%PCBDCU（relative to PCBM）,the device parameters based on P3HT:PCBM:PCBDCU or PTB7-Th:PC₇₁BM:PCBDCU as the active layer were obviously enhanced.（4）An interface stabilizer based on alkylation-functionalized fullerene derivatives PCB-C8oc was successfully applied as the additive in the active layer of OSCs.The PCB-C8oc could distribute on the interface of donor and acceptor.The octyl groups of PCB-C8oc exhibited intermolecular interaction with the alkyl chain of P3HT or PTB7,and the fullerene unit of PCB-C8oc was in tight contact with PCBM.The dual functions of PCB-C8oc will inhibit the excessive phase separation between electron donor and acceptor,thereby improving the stability of devices under long-time thermal annealing at high temperature.When doped with 10 wt%PCB-C8oc,the PCE of the P3HT system decreased from 3.54%to 2.88%after 48 h of thermal treatment at 150°C,whereas the PCE of the reference device without PCB-C8oc dramatically dropped from 3.53%to0.73%.For the PTB7:PCBM-based devices,after adding only 5 wt%PCB-C8oc,the OPVs also exhibited thermally stable morphology and better device performances after 12h of thermal treatment at 150°C.（5）The small molecule TM25 was used as secondary donor in ternary OSCs.The introduction of TM25 can broaden the absorption spectra of PBDB-T:IT-M blend and improve the absorption of the sunlight.The open circuit voltage was gradually enhanced with the doping concentration of TM25.So,the working mechanism of TM25 can be explained by the parallel model,that is,the secondary donor TM25 has its own charge network system which can generate excitions and transport charge.As a result,the ternary OSCs with 20 wt%TM25 shows a proper PCE of 11.6%.