Study On Polymer Solar Cells With Cesium Doped Zinc Oxide Electron-Transporting Layer

Polymer solar cells(PSCs) have received considerable attentions due to their advantages such as low cost, lightweight and flexibility. To improve the performance of PSCs, many research have been focused on the design and synthesis of new materials, interface engineering control, developing new device architectures. Interfacial layers between the active layer and electrodes are commonly employed to improve the efficiency of carriers collection. And solution-processed n-type Zn O film is widely used as electron transporting layer(ETL) between the active layer and ITO cathode in PSCs, due to its air stability, optical transparency and non-toxicity. However, the power conversion efficiency(PCE) of PSCs was still lower, owing to the low electron transporting ability of Zn O film due to the low temperature process.In this thesis, cesium doped Zn O(CZO) films was used as ETL for PSCs to improve the electrical conductivity. On the other hand, to diminish the energy barrier between the ETL and the active layer, surface modification for CZO film had been investigated using ethanolamine(EA) as a surface modifier. To increase the contact area between the active layer and ETL and further enhance the electron transporting ability, PSCs with Zn O nanorod ETL were fabricated and investigated. The introduction of vertically aligned Zn O nanorods can improve charge transport in the devices since they can act as well-defined charge transport paths with high carrier mobilities, reduce the bimolecular recombination and increase the thickness of active layer which is helpful to trap the incident light into the active layer. The doping of cesium and surface modification with EA solution were also used to improve the performance of PSCs. The detail results are as following:1. The CZO film was prepared by using sol-gel process and introduced in the PSC as ETL, surface modification for CZO film also was investigated to improve the interface contact quality between the active layer and CZO layer. The conductivity of 0.005 M CZO film was one order of magnitude higher than that of undoped Zn O film, the PCE of PSCs based on the configuration of ITO/CZO/P3HT:PC61BM/Mo O3 /Al was enhanced from 2.98% to 3.48%. Then the EA surface modifier was inserted between the CZO film and active layer to further improve the contact interface quality, the EA could spontaneously arise on Zn O film surface and formed an interfacial dipole layer, which resulting in the suppression of bimolecular recombination and enhancement of electron extraction. The PSC device using 1% EA modified 0.005 M CZO film as ETL showed the best performance and further enhanced the PCE to 4.03%.2. The CZO nanorod was processed by chemical bath deposition and introduced in the PSC as ETL, the device configuration was ITO/CZO nanorod/P3HT:PC61BM/ Mo O3/Ag. The PCE of the device was enhanced 50% by using 0.75 m M CZO nanorod as ETL. The surface modification for CZO nanorod also was investigated to improve the interface contact quality between the active layer and CZO nanorod. The PCE was enhanced to 2.99% by using 2% EA modified 0.75 m M CZO nanorod as ETL.In this thesis, Cs doping technique and surface modification by EA had been introduced during the fabrication of Zn O film and nanorod as ETL for PSC to improve their performance. This is a valid way to fabricate the high efficiency PSC and has a good application prospect.