Universal Features of Electron Dynamics in Solar Cells with TiO₂ Contact: From Dye Solar Cells to Perovskite Solar Cells

The electron dynamics of solar cells with mesoporous TiO₂ contact is studied by electrochemical small-perturbation techniques. The study involved dye solar cells (DSC), solid-state perovskite solar cells (SSPSC), and devices where the perovskite acts as sensitizer in a liquid-junction device. Using a transport-recombination continuity equation we found that mid-frequency time constants are proper lifetimes that determine the current–voltage curve. This is not the case for the SSPSC, where a lifetime of ∼1 μs, 1 order of magnitude longer, is required to reproduce the current–voltage curve. This mismatch is attributed to the dielectric response on the mid-frequency component. Correcting for this effect, lifetimes lie on a common exponential trend with respect to open-circuit voltage. Electron transport times share a common trend line too. This universal behavior of lifetimes and transport times suggests that the main difference between the cells is the power to populate the mesoporous TiO₂ contact with electrons

Universal Features of Electron Dynamics in Solar Cells with TiO₂ Contact: From Dye Solar Cells to Perovskite Solar Cells

The electron dynamics of solar cells with mesoporous TiO₂ contact is studied by electrochemical small-perturbation techniques. The study involved dye solar cells (DSC), solid-state perovskite solar cells (SSPSC), and devices where the perovskite acts as sensitizer in a liquid-junction device. Using a transport-recombination continuity equation we found that mid-frequency time constants are proper lifetimes that determine the current–voltage curve. This is not the case for the SSPSC, where a lifetime of ∼1 μs, 1 order of magnitude longer, is required to reproduce the current–voltage curve. This mismatch is attributed to the dielectric response on the mid-frequency component. Correcting for this effect, lifetimes lie on a common exponential trend with respect to open-circuit voltage. Electron transport times share a common trend line too. This universal behavior of lifetimes and transport times suggests that the main difference between the cells is the power to populate the mesoporous TiO₂ contact with electrons

Morphology and Kinetics of Aggregation of Silver Nanoparticles Induced with Regioregular Cationic Polythiophene

The aggregation kinetics of negatively charged borate-stabilized silver nanoparticles (NPs) induced by the cationic regioregular polythiophene polyelectrolyte poly­{3-[6-(1-methylimidazolium-3-yl)­hexyl]­thiophene-2,5-diyl bromide} (PMHT-Br) and the morphology of formed aggregates have been investigated via ultraviolet–visible light (UV-vis) spectroscopy, transmission electron microscopy (TEM), zeta (ζ) potential measurements, dynamic light scattering (DLS), and time-resolved small-angle X-ray scattering (SAXS). Two or three populations of NPs are formed within milliseconds upon mixing the components, which differ in the mean size, extent of polymer coating, and time stability. These characteristics are primarily controlled by the PMHT-Br to Ag-NPs ratio. Population of single NPs of a mean size of ∼5 nm is present in every system and is mostly stable for a long time. At low ratios, the single NPs are most probably almost free of polymer chains and the second population includes slow, but in a limited extent, growing NPs in which single NPs might be interconnected by polymer chains. At the ratios corresponding to the charge balance in the system (ca. zero ζ-potential of NPs), the NPs aggregate, forming a second population that continuously grows in size, and finally undergo sedimentation. At the high ratios, three long-time stable populations of NPs are observed, having mean sizes of ca. 5, 13, and 35 nm; all NPs should be fully coated with PMHT-Br, giving them a positively charged stabilizing shell

Triazatruxene-Based Hole Transporting Materials for Highly Efficient Perovskite Solar Cells

Four center symmetrical star-shaped hole transporting materials (HTMs) comprising planar triazatruxene core and electron-rich methoxy-engineered side arms have been synthesized and successfully employed in (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite solar cells. These HTMs are obtained from relatively cheap starting materials by adopting facile preparation procedure, without using expensive and complicated purification techniques. Developed compounds have suitable highest occupied molecular orbitals (HOMO) with respect to the valence band level of the perovskite, and time-resolved photoluminescence indicates that hole injection from the valence band of perovskite into the HOMO of triazatruxene-based HTMs is relatively more efficient as compared to that of well-studied spiro-OMeTAD. Remarkable power conversion efficiency over 18% was achieved using 5,10,15-trihexyl-3,8,13-tris­(4-methoxyphenyl)-10,15-dihydro-5<i>H</i>-diindolo­[3,2-<i>a</i>:3′,2′-<i>c</i>]­carbazole (<b>KR131</b>) with compositive perovskite absorber. This result demonstrates triazatruxene-based compounds as a new class of HTM for the fabrication of highly efficient perovskite solar cells