Improving The Performance And Stability Of Polymer Solar Cells By Inserting Electron Transfer Layer

Polymer solar cells(PSCs) have attracted a great deal of research attention in the recent years owing to their low-cost and easy-processing features. Although the PSCs have been developed rapidly in the past decades, the power conversion efficiency(PCE) and device stability are still the bottlenecks for the large-scale applications. To solve these two problems, in addition to the continuous innovation and improvement of active layer material, the optimization of interface layer also plays a vital role. In this thesis, we mainly adopt two kinds of different methods to modify ITO: one is covalent surface grafting of aziridine; the other is spin-coating acridine orange hydrochlor hydrate(AOHH) as electron transfer layer(ETL). By using these two interlayers, the device performance and stability were improved.1. Lowering the work function(WF) of ITO by covalent surface grafting of aziridine: application in inverted PSCs. In order to enhance the solvent resistance of the ETL and achieve high-performance PSCs, the ITO substrates were covalently modified with surface grafting hyper-branched polymer of aziridine(SGHPA), 3-aminopropyltriethoxysilane(APTES), and the two layered film with SGHPA on top of APTES(SGHPA@APTES). The surface grafting polymerization of aziridine was employed to covalently modify the ITO substrates, by which the WF of the ITO was dramatically lowered, and the PCEs of the inverted PSCs were significantly improved. A champion PCE of 8.18% has been achieved, which increases 76% comparing with the PCE of 4.65% of the inverted PSC without ETL. Moreover, with the covalently bonded ETL, the stability of the inverted PSCs is greatly enhanced.2. The conjugated molecule AOHH was employed as ETL in both conventional and inverted PSCs. With existence of the AOHH layer, the surface WF of ITO can be lowered by 0.6 eV. The modified ITO substrates were applied in both PSCs with conventional and inverted configuration. The results showed that the PCE of the conventional PSCs were increased significantly. For the PSCs with conventional configuration, a champion PCE of 6.97% has been achieved, whereas the PCE of the device without ETL was 6.29%. For PSCs with inverted configuration, a champion PCE was 6.97%.In conclusion, the organic materials can effectively improve the device performance and air stability of PSCs. We hope that this work may lead to a new avenue for developing the covalently modified ETLs and solution processing material as ETLs, which can not only be used in PSCs, but also be extended to new types of solar cells.