Effect Of Rapid Thermal Annealing Of ZnO Nanorods Buffer Layer On The Performance Of Polymer Solar Cells

Polymer solar cells(PSCs)have been favored by the majority of scientific researchers because of the advantages of low cost,flexible substrate fabrication and large area production.Inverted polymer solar cells(IPSCs),which replace air-sensitive Al cathode with more stable Au or Ag top anode and eliminate the use of PEDOT:PSS,improve the device stability and lifetime significantly.In recent years,IPSCs incorporating Zn O nanorod arrays(Zn O-NRAs)as cathode buffer layer(CBL)or acceptor have been considered as an “ideal” architecture that facilitate the carrier extraction and transportation.Embedded deep into polymer light absorber,the Zn O-NRAs increases the interface area between active layer and CBL and provides a robust electron transport path with high carrier mobility.However,both the sol-gel method for the fabrication of seed layer and the hydrothermal synthesis of Zn O-NRAs are low-temperature process and thus the one-dimensional nanorod arrys prepared is defect dominant and has poor crystallinity.The performance of IPSCs based on Zn O-NRAs is far from satisfactory and the power conversion efficiency(PCE)of the device has not been improved significantly compared to that of the IPSCs using Zn O film as CBL.In this thesis,rapid thermal annealing(RTA)technique was introduced to post-treat Zn O seed layer and Zn O-NRAs.Annealed at high temperature within a few seconds,the crystallinity of Zn O-NRAs and the performance of IPSCs can be greatly improved without damage to the substrate.The specific content of this thesis is as follows:First,The IPSCs with the configuration of ITO/Zn O-NRAs/P3HT:PCBM/Mo O3/Ag and ITO/Zn O-NRAs/PTB7:PC71BM/Mo O3/Ag were prepared and the processing parameters were optimized.The results show that the device PCE is maximal when the growth solution concentration is 0.040 mol/L.Compared to that of IPSCs using Zn O thin film as CBL,the short-circuit current of the IPSCs with the structure mentioned above was increased from 9.6 m A/cm2 to 12.0 m A/cm2,14.5 m A/cm2 to 17.6 m A/cm2 andthe PCE was increased from 2.95% to 2.95%,5.77% to 6.01% separately.Second,Zn O-NRAs CBL was treated with RTA and the effect of annealing temperature and time on the performance of IPSC with the structure of ITO/Zn ONRAs/PTB7:PC71BM/Mo O3/Ag was investigated.The results show that the PCE of the IPSC was 16% higher than that of the device using Zn O thin film as CBL and reached 7.0%when RTA temperature and time was 500℃ and 15 s separately.Finally,in order to further improve the device performance,the Zn O seed layer and Zn O-NRAs was RTA treated subsequently and the IPSC with the structure of ITO/Zn O-NRAs/PTB7:PC71BM/Mo O3/Ag was prepared.When the Zn O seed layer and Zn O-NRAs were annealed at 500℃ for 15 s,the short-circuit current of the IPSC was 19.2 m A/cm2 and the PCE reached7.7%,which was 20% higher compared to the IPSC device which treated Zn O-NRAs with RTA only.In this thesis,Zn O-NRAs was introduced as the cathode buffer layer in IPSC devices and both Zn O seed layer and Zn O-NRAs were post-treated with RTA technique to improve the crystallinity of the CBL.Compared with the traditional thermal annealing process,the device performance has been improved significantly and the post-treatment proposed here provides an effective way to fabricate low-cost,large scaling and easy processing IPSC devices.