Research Of Novel Additives Processed Active Layers For Polymer Solar Cells

Polymer solar cells(PSCs)have attracted great attention because of their advantages of low cost,flexibility,light weight and simple fabrication,which are compatible with the demands of large-scale manufacture.Recently,the highest power conversion efficiency(PCE)of single junction PSCs have exceeded 18%.With the development of the material system,it is necessary to simplify the device processing,improve the active layer thickness processing window and enhance the stability of devices.It is proved that solvent additives play an important role in improving the photovoltaic performance of PSCs,which is also a simple and effective strategy.However,some issues are still existed in traditional solvent additives,such as remaining in the active layer because of their high boiling points(bp.),high toxicity of some halogen solvent additives and so on,which require some new solvent additives to be developed.In this paper,some new solvent additives have been developed and applied to the processing of PSCs especially non-fullerene solar cells.In the first chapter,we introduced the development of PSCs and their solvent systems,while the fabrication and test of devices were described in second chapter.For developing new additives,the following works have been done:In the third chapter,two low bp.additives 1,1-Dimethoxyethylbenzene(DMB)and 6-Mercapto-1-hexanol(MHA)were used in the active layer processing of non-fullerene system.Compared with the traditional additives,the two additives have lower bp.,which can be removed easily from the active layer,so additional processes such as vacuum evaporation can be avoided.Herein,DMB and MHA were applied in the processing of PTB7-Th:EH-IDTBR non-fullerene active layer.The two additives afforded better device performance,higher efficiency of thick film devices,and superior device stability.Structurally,DMB is an aromatic additive while MHA is a nonconjugated additive,which showed a great difference in modifying morphology of the active layer.The MHA based blend film had larger domain size than the DMB based blend film.This is related to their different solubilities to the PTB7-Th and EH-IDTBR components.An optimal PCE of 11.36%was obtained in the MHA based thin film device,higher than the 10.41%of as-cast device.Therefore,the results showed that DMB and MHA have great potential to improve the performance of non-fullerene solar cellsIn the fourth chapter,a nonhalogenated solvent system based on host solvent o-xylene(o-XY)and low boiling solvent additive butyl phenyl ether(BPE)was used to modify several non-fullerene active layers.As a result,the device efficiency based on the nonhalogenated solvent system was approached to that of the traditional halogenated solvent system(chlorobenzene with 1,8-diiodooctane).Towards J35Si:IT-4F active layer,the device efficiencies based on single solvent o-XY,nonhalogenated solvent system and traditional solvent system were 11.78%,12.81%and 12.86%,respectively.These results indicated the great potential of this nonhalogenated solvent system in processing non-fullerene PSCs.In the fifth chapter,we investigated the effect of hindered amine stabilizer on the thermal stability and light stability of PTB7-Th:PC71BM system.We found that adding 2%hindered amine N,N'-(Hexane-1,6-diyl)bis(N-(2,2,6,6-tetramethylpiperidin-4-yl)formamide(HTPF)can significantly improve the device current from 16.74 mA/cm2 to 18.11 mA/cm2,and the corresponding PCE can be elevated from 9.10%to 9.45%.In addition,the thermal stability and light stability of the device were improved mainly because of the short-circuit current was well retained.The Fourier transform infrared spectroscopy(FTIR)spectrum shows that HTPF may form hydrogen bonds with the donor and acceptor,which can slow down the aggregation of fullerenes and prevent the expansion of domain size when the device suffered the heat or light,improving the stability of the device.