Research Of High Efficiency Ternary Organic Solar Cells Based On PTB7: PC₇₁BM System

The concept of ternary organic solar cell(TOSC)is a promising strategy to improve the performance of organic solar cell and more and more research groups around the world focus on it in recent years.In this paper,a small molecule Rubrene and a conjugated polymer poly{2,2’-(2,5-bis(2-octyldodecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)dithieno[3,2-b]thiophene-5,5’-diyl-alt-thiophe n-2,5-diyl}(PDPPBTT)are used as the third material into the dominating poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl})(PTB7): [6,6]-phenyl C71-butyric acid methyl ester(PC71BM)system to fabricate TOSC,respectively.Firstly,the effect of the small molecule Rubrene on the performance of PTB7: Rubrene: PC71 BM TOSC was investigated.Under a low Rubrene doping ratio of 1.0 wt%,the optimized device was achieved,resulting in a 21.7% improvement in power conversion efficiency from 6.60% to 8.03%.Improved photovoltaic performance of TOSC was mainly due to improved charge transportation by appropriate energy cascade alignment and enhanced light harvesting by strong Fo?rster resonance energy transfer from Rubrene to PTB7.Moreover,the appropriate location of Rubrene in the ternary blends optimized the blend morphology.Furthermore,the impedance spectroscopy results indicated that the incorporation of Rubrene can increase the number of photoconductive carriers and suppress the bimolecular recombination.Secondly,the effect of the conjugated polymer PDPPBTT on the performance of PTB7: PDPPBTT: PC71 BM TOSC was investigated.Under a low PDPPBTT doping ratio of 0.5 wt%,the optimized device was achieved,resulting in a 21.6% improvement in power conversion efficiency from 6.49% to 7.89%.Improved photovoltaic performance of TOSC was mainly attributed to good absorption in the infrared region,appropriate energy cascade alignment,efficient Fo?rster resonance energy transfer from PTB7 to PDPPBTT,and more balanced hole-electron mobility.Moreover,as a third component,PDPPBTT enhanced the crystallinity of PTB7 and optimized the morphology of ternary blends.It was also found that the incorporation of PDPPBTT increased the charge carrier lifetime,ensuring efficient charge carrier transport and collection with suppressed bimolecular recombination.In summary,the results of this work indicate that using small molecule Rubrene or conjugated polymer PDPPBTT as the third component in PTB7: PC71 BM blend is an effective method to improve the efficiency of organic solar cell.This work provides an effective solution for the realization of high performance TOSC.