Charge carrier dynamics in PffBT4T-2OD: PCBM organic solar cells.

Abstract We investigate the charge carrier dynamics of inverted organic solar cells (OSCs) based on PffBT4T-2OD: PCBM and PTB7: PCBM – the two leading systems among the OSCs based on polymer-fullerene bulk-heterojunction – to elucidate the origin of their performance difference. Transient absorption spectroscopy (TAS) and photo-electrochemical impedance spectroscopy (photo-EIS) were employed to unravel the photo-physics that govern the cell operation of these two highly efficient bulk heterojunction OSCs. While photo-EIS indicates that the two systems under study exhibit similar behavior in terms of recombination, TAS results reveal that PffBT4T-2OD: PCBM systems not only have higher charge generation rate but also more efficient charge transfer than PTB7: PCBM systems, leading to the power conversion efficiency of PffBT4T-2OD: PCBM-based OSCs (9.16%) that is higher than that of PTB7: PCBM-based OSCs (6.44%). Graphical abstract Image 1 Highlights • Charge carrier dynamics of PffBT4T-2OD: PCBM and PTB7: PCBM OSCs have been compared. • TAS and Photo-EIS measurements along with optical simulation were carried out. • Higher PCE for PffBT4T-2OD: PCBM OSCs is due to better absorption and carrier collection efficiency. [ABSTRACT FROM AUTHOR]