The nature of excitons in PPDT2FBT:PCBM solar cells: Role played by PCBM

Abstract

In organic semiconductor based bulk heterojunction solar cells, the presence of acceptor increases the formation of charge transfer (CT) excitons, thereby leading to higher exciton dissociation probabilities. In this work we used steady state electroabsorption (EA) measurements to probe the change in the nature of excitons as the blend composition of the solar cell active layer material is varied. We investigated blends of poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) and (6,6)-Phenyl C71 butyric acid methyl ester (PCBM). Analysis of the EA spectra showed that in presence of fullerene based acceptor, like PCBM, CT characteristics of the excitons were modified, though, no new CT signature was observed in the blend. Enhancement in the CT characteristic in the blend was reflected in the photoluminescence (PL) measurements of the blends, where, PL quenching of $\sim$ 63\% was observed for 1\% PCBM. The quenching reaches saturation at about 20\% PCBM. However, efficiency of the device increased with PCBM percentage beyond 20\%. The maximum efficiency was obtained for the blend having 50\% PCBM, among the blend compositions studied in this work, indicating the optimum concentration of PCBM for best power conversion efficiency to be around that value. Comparing experimental results with simulations, the variation of the device efficiency with PCBM percentage was shown to be arising from multiple factors like increase in polarizability and dipole moment of excitons, and the efficiency of the carrier collection from the bulk of the active layer.

Exploring pristine and transition metal doped SiP2 monolayer as a promising anode material for metal (Li, Na, Mg) ion battery

“…Graphene is the lightest 2D material reported for LIBs. For LIB electrode materials many well-known 2D materials -such as phosphorene, 7,8 arsenene, 9 transition metal dichalcogenides (TMDs), 10,11 transition metal carbides, 12 and nitrides (MXenes), 13 transition metal oxides, 14,15 Janus transition metals 16,17 have been synthesized and investigated. While many new 2D material families are being explored in lithium-ion battery technology, the lithium atom content on Earth is limited.…”

Spectroscopic Identification of the Charge Transfer State in Thiophene/Fullerene Heterojunctions: Electroabsorption Spectroscopy from GW/BSE Calculations

“…19 EA spectra are commonly fitted to first and second derivative lineshapes of the linear optical absorption spectrum. 20 external field are used to explain how first and second derivative lineshapes arise in EA spectra of model systems constructed from ammonia and borane molecules. ΔA(ω) is the change in linear optical absorption spectrum induced by an external electric field.…”

“… 19 EA spectra are commonly fitted to first and second derivative lineshapes of the linear optical absorption spectrum. 20 Splittings of FR states induced by the Coulomb interaction in excited singlet states and strong changes in wave function character of CT states induced by an external field are used to explain how first and second derivative lineshapes arise in EA spectra of model systems constructed from ammonia and borane molecules. Δ A (ω) is the change in linear optical absorption spectrum induced by an external electric field.…”

“…Signals attributed to CT states in these systems have been observed in EA spectroscopy. 20 , 23 , 28 , 29 However, polaron absorption in conjugated polymers also lies in the range 1.0 to 1.6 eV, where CT states also lie. Polaron optical absorption in a conjugated polymer has recently been reinterpreted.…”

Density functional theory study on the interaction of C60 fullerene with PCBM

“…[1][2][3][4][5][6] The most common fullerene derivative in organic electronics is Phenyl-C 61 -butyric acid methyl ester (PCBM). [7][8][9][10] Various similar compounds, such as C 60 , have been synthesized and used as n-type semiconductors. For a decade, PCBM has been investigated for use in various thin-film organic electronics applications.…”