Effect Of Interface Modification On The Performance Of Organic Solar Cells

Organic solar cells have been considered as a potential candidate for energy crisis and environmental pollution owing to low cost,simple preparation process,large area preparation,application to flexible devices and extensive sources of organic materials.In this paper,we present a systematic investigation of the effect of cathode interface modification on the performance and stability of organic solar cells;the main research contents include three parts as follows:(1)We report the fabrication of high performance inverted polymer solar cells(PSCs)with simply modified indium tin oxide(ITO)by an ultrathin aluminium(Al)and sodium chloride(NaCl),not only realizing high efficiency,but also greatly improving stability.The optimized device with P3HT: PCBM as the active layer under AM 1.5(100 mw cm-2)radiation achieved a high power conversion efficiency(PCE)of 3.88%,which is significantly higher than those of the inverted devices with only Al or NaCl as modification interlayer,respectively.More importantly,the stability is enhanced by about 1.7 times of the conventional device.The significant enhancement is attributed to the reduction of the work function of ITO electrode from 4.75 to 3.90 eV and the improvement of electrode interface.(2)The effect of organic small molecule cathode buffer layer on the performance and stability of organic optoelectronic devices was studied based on a blend of P3 HT and PCBM.Four kinds of cathode buffer layers: BCP,TPBi,Alq3 and Tm PyPB were inserted between the active layer and cathode,which played a leading role in the device’s performance.The performance of the device is greatly improved by using the cathode buffer layer above.The stability of these devices was further studied.The results indicated that device with cathode buffer layer TmPyPB exhibited better stability than other organic cathode buffer layers.Fifteen days later the device efficiency is still more than 80% of the original data,which can be comparabled with the inorganic materials.(3)Methods of solvent vapor and airflow annealing to deal with buffer layer ZnPc(OC8H17OPyCH3I)8 films on cathode of the inverted organic solar cells based on P3HT: PCBM were studied to investigate the effect of the annealing treatment methods on the device performance.Results indicate that annealing treatment can effectively improve the morphology of the buffer layer as demonstrated by atomic force microscopy(AFM).The PCE of the solar cell is improved from 2.14% to 3.76%,the Jsc increases from 8.12 mA/cm2 to 10.71 mA/cm2,and the FF is improved from 0.45 to 0.61 for the annealing process.More importantly,the stability is enhanced,with the device life being 1.4 times that of the conventional device.This simple cathode interface treatment method provides an effective way to improve the performance of polymer solar cells.