Parameters Influencing the Efficiency of Electron Injection in Dye-Sensitized Solar Cells

Abstract

In this paper we focus upon the electron injection dynamics in complete dye sensitized nanocrystalline titanium dioxide solar cells (DSSCs) employing the ruthenium bipyridyl sensitizer dye N719. Electron injection dynamics and quantum yields are studied by time resolved single photon counting and the results are correlated with device performance. In typical DSSC devices, electron injection kinetics were found to proceed from the N719 triplet state with an half time of 200 ± 60 ps and quantum yield of 84 ± 5 %. We find that these injection dynamics are independent of presence of iodide / triiodide redox couple and of the pH of the peptisation step used in the synthesis of the TiO 2 nanoparticles. They are furthermore found to be only weakly dependent upon the application of electrical bias to the device. In contrast, we find these dynamics to be strongly dependent upon the concentration of t-butyl pyridine (tBP) and lithium cations in the electrolyte. This dependence is correlated with shifts of the TiO 2 conduction band energetics as a function of tBP and Li + concentration, from which we conclude that a 100 meV shift in band edge results in approximately a two fold retardation of injection dynamics.We find that electron injection quantum yield determined from these transient emission data as a function of tBP and Li + concentration shows a linear correlation with device short circuit density J sc . We thus conclude that the relative energetics of the dye excited state versus the titanium dioxide acceptor states is a key determinant of the dynamics of electron injection in DSSC, and that variations in these energetics, and therefore in the kinetics and efficiency of electron injection, impact directly upon device photovoltaic efficiency. Finally we discuss these results in terms of singlet versus triplet electron injection pathways and the concept of minimisation of kinetic redundancy.

Ultrafast characterization of the electron injection from CdSe quantum dots and dye N719 co-sensitizers into TiO2 using sulfide based ionic liquid for enhanced long term stability

“…48 The component of the fast injection process measured here is as large as 76%, suggesting that the latter explanation is more reasonable. [47][48][49] As shown in Fig. 1(b), the TG response of N719 on TiO 2 measured in IL showed no qualitative change with respect to the electrode in air, see Fig.…”

“…Therefore, the "apparent disappearance" of the fastest decay processes in the IL electrolyte implies that the hole trapping/transfer to the S 2-ions, which are supposed to be strongly adsorbed onto the CdSe QD surface, can be too fast in these 47 The fast rise of the TG signal shown in Fig. 1(b 48,49 It has been reported that the electron injection rate from the singlet excited state of N719 to metal oxide electrodes is one order of magnitude faster than that from the triplet state. 38,46 Another explanation could be that both the two injection processes mostly correspond to electron injection processes from the triplet excited state due to some inhomogeneities in the TiO 2 nanoparticle surfaces, resulting in different electronic couplings between N719 and the TiO 2 .…”

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

“…These shifts occur when the acid/base characteristics of the electrolyte are changed intentionally, or change with time or light exposure. 41,42 . In DSSCs the shift in the capacitance curves has been assigned to adsorption/desorption of ions or dipoles that change the electric field between the TiO 2 and the electrolyte.…”

Spin–orbit coupling and Lorentz force enhanced efficiency of TiO2‐based dye sensitized solar cells

“…The relaxation for the spin selection rule through an intersystem crossing can take place by introducing the spin -orbit (s -o) coupling. [13] Over here the quantum state of the system is given by the total angular momentum, J = L + S, which may give weak spin forbidden bands with an overlap between the excited singlet excitonic levels and the excited triplet excitonic levels. Normally such an intersystem crossing enhances if the system consists of heavy atom molecules with a strong s -o coupling and in the presence of paramagnetic elements.…”

“…Here, we make use of the Di-tetrabutylammonium cisbis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II) photo sensitizer or commonly known as the N719 dye. The choice of N719 dye as the sensitizer for our studies has been motivated by the fact that the electron injection dynamics (EID) in the N719/TiO 2 system has been extensively studied in previous reports [13,[16][17][18] and hence there is a general consensus on the bi-phasic injection kinetics from the N719 dye LUMO to the TiO 2 acceptor states.…”