Performance Study Of Flexible Organic Solar Cells Based On PEDOT:PSS Electrode

Organic solar cells(OSCs)are considered as a new generation of green energy technology with great industrial prospects because of their light weight,low cost,flexibility and large area preparation.Among them,flexible organic solar cells have attracted significant attentions because of their future prospects in wearable energy and building integrated photovoltaic energy.ITO(indium tin oxide)is the most widely used electrode material because of its high transmittance and conductivity.However,this material is brittle,easy to crack,scarce and has both complex manufacturing process and poor mechanical performance,which limited its application for low-cost,flexible large-area optoelectronic devices.Therefore,it is urgent to find a new transparent conductive electrode to replace ITO in the field of flexible organic optoelectronics.Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PEDOT:PSS)conductive polymer is considered as one of the most promising flexible transparent conductive electrodes because of its high light transmittance,good flexibility,high work function(5eV)and good thermal stability.However,the pristine PEDOT:PSS films cannot meet the requirements of transparent electrode materials due to their low conductivity.Although a lot of research has been done to improve the conductivity of PEDOT:PSS,there were still some shortcomings,which need to be further overcame.At present,the method of wet processing films is spin coating,but it is not suitable for large-area manufacturing.Furthermore,its low material utilization and other shortcomings have made it to be unsuitable for large-area flexible organic solar cells.Drop coating is a simple and fast film preparation process,which has high material utilization rate and matches with large area preparation technology.In this paper,we use drop coating method to prepare modified PEDOT:PSS film as an anode in organic solar cells to explore its influence on the photovoltaic performance of organic solar cells.The main contents are as follows:(1)A series of PEDOT:PSS thin films doped with different concentration of ethylene glycol(EG)with an area of about 5.0 cm~2 were prepared by drop coating method.The effects of different doping concentration on the properties of PEDOT:PSS films were investigated.The experimental results showed that when the doping concentration is 6%,the quality factor(FoM)of the prepared PEDOT:PSS films can be increased from 0.059(undoped)to 47.24.The reasons for the improvement of the quality factor of PEDOT:PSS films were analyzed by means of ultraviolet-visible transmission spectroscopy,atomic force microscopy(AFM),X-ray photoelectron spectroscopy(XPS).The results showed that the morphology of PEDOT:PSS films doped with EG has changed.Doping can effectively separate the PEDOT and PSS in the films,promote PEDOT to form a double continuous interpenetrating network structure,which is conducive to charge transfer and thus improve the conductivity of the films.The fill factor(FF)and photoelectric conversion efficiency(PCE)are 66.12%and 8.89%respectively for the normal flexible organic solar cells prepared by drop coating method,which are close to the efficiency of the same devices prepared by spin coating method and slightly lower than that of the rigid devices using ITO as the anode.(2)On the basis of the previous experiment,five kinds of PEDOT:PSS films were prepared by drop coating method,including dimethyl sulfoxide(DMSO),ethylene glycol(EG)doping,methanesulfonic acid(MSA)surface treatment and the combination of the two treatments.It was found that the properties of the films treated by double treatment were better than those treated by single treatment,and the FoM value of PEDOT:PSS films treated by DMSO/MSA was the highest,reaching 64.35.Through a series of characterization of film properties,it was found that the doping of DMSO and EG polar solvents resulted in the phase separation of PEDOT and PSS in the film.MSA treatment reduced the PSS composition of insulation in the film,thus improving the conductivity of the film.These films were used as transparent anodes instead of ITO glass to fabricate organic solar cells on flexible PET substrates.Among them,the FF of DMSO/MSA treated PEDOT:PSS films as electrodes reached 70.74%and PCE reached 10.23%,which was higher than that of single treatment,and the efficiency of flexible devices fabricated by spin coating was almost the same as drop coating method.The efficiency of all-wet fabrication of flexible devices by drop coating method is more than 10%.It shows good application prospects in the field of flexible large-area fabrication of organic optoelectronics.