Cathode Interface Engineering In Polymer Solar Cells And Fabrication Of Ultrathin Metal Transparent Electrodes

Polymer solar cells(PSCs)have attracted much attention as a result of their light weight,low cost,high mechanical flexibility,and large area devices fabrication through roll-to-roll techniques.The power conversion efficiency(PCE)of PSCs has improved rapidly over the past few years with the development of new conjugated polymers and donor,the application of new devices structure and interface engineering.And the highest PCE of single-junction PSCs has exceeded 12%.However,PSCs are still inferior to inorganic thin film photovoltaics in efficiency and stability.To further improve the performance of PSCs,the leitmotif of this work is achieving high performance PSCs by cathode interface engineering and fabricating ultrathin metal transparent electrodes,and the main studies are summerized as follows:(1)Water-or alcohol-soluble polymer PFEOSO3Na was introduced to conventional PSCs as cathode interlayers(CILs).By optimizing devices preparation process,PFEOSO3Na CILs were well applied in PSCs based on P3HT:PCBM,PCDTBT:PC71BM,PBDTTT-C:PC71BM,PDPP3T:PCBM and PTB7:PC71BM active layers.These results demonstrated the universality of PFEOSO3Na CILs.The absorption of PDPP3T:PCBM film and a-Si film was very complementary.The spectral range of organic/a-Si hybrid tandem device based on PDPP3T:PCBM Bottom-cell and a-Si Top-cell was extended to 950 nm.And PFEOSO3Na CILs was used to modify PDPP3T:PCBM based organic solar cell.A high PCE of 7.49%was obtained for organic/a-Si hybrid tandem solar cells.PFEOSO3Na CILs were dissolved in methanol.Methanol treatment on PTB7:PC7iBM active layer could improve the surface potential of active layer and riched PC71BM at the surface of PTB7:PC71BM active layer.Conventional polymer solar cells based on PTB7:PC71BM with power conversion efficiencies increased to>9%by methanol treatment and PFEOSO3Na CILs was obtained.(2)ZnO/PFEOSO3Na double CILs were used to fabricate high performance inverted PSCs.Compared to ZnO modified ITO,ITO modified by ZnO/PFEOSO3Na possessed high transmittance,smoothened surface,and lower work function.And the electron mobility in the ZnO/PFEOSO3Na films was higher than that in the ZnO films.ZnO/PFEOSO3Na double CILs modified devices achieved lower dark current and possessed more favorable energy level alignment.Inverted PSCs based on PTB7:PC7iBM containing ZnO/PFEOSO3Na double CILs exhibited a high PCE of 8.49%,exceeding that of the control devices with ZnO CILs(7.48%).Meanwhile,PTB7-Th:PC7iBM inverted PSCs containing ZnO/PFEOSO3Na double CILs achieved a high PCE of 9.41%.(3)Low cost 1-Pyrenemethanol(PyM)was firstly introduced to modify ZnO in inverted PSCs.Intimate interfacial contact was developed between PyM and ZnO,which was attributed to the hydrogen bond interaction between PyM and ZnO.PyM could be self-assembled on ZnO surface and the surface of ZnO could be well modified by PyM.The electron mobility of ZnO/PyM modified devices was an order of magnitude higher than that in the ZnO modified devices.PTB7-Th:PC7iBM devices modified by ZnO/PyM CILs achieved a high PCE of 8.27%,improved about 20%compared to ZnO modified control devices.The introduction of PyM could efficiently improve Jsc and FF.And the PCE of PTB7-Th:PC7iBM devices modified by ZnO/PyM CILs was insensitive to the thickness of PyM,which was benefited for large area devices fabrication through roll-to-roll techniques.ZnO/PyM CILs was also applied in PSCs based on PTB7:PC7iBM.And ZnO doped with PyM also well applied in inverted PSCs based on PTB7:PC71BM.(4)Ultrathin metal transparent electrodes were constructed by thermal evaporation.The introduction of 2 nm Au seed layer made it possible to develop a continuous Ag film with only 4 nm Ag.Glass/MoO3(3nm)/Au(2nm)/Ag(4nm)possessed much homogenous surface than ITO glass.ZnO film could not only improve the transmittance of metal electrode but also modify the work function of it.27 nm ZnO film modified metal electrode had an average transmittance up to 80%from 480 to 680 nm,and the ultrathin metal electrode could be directly used as cathode in polymer solar cell,a PCE of 5.20%was achieved in PTB7:PC71BM based inverted polymer solar cell.