Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic ...neutron scattering measurements showing that dipolar CH3NH3(+) ions reorientate between the faces, corners or edges of the pseudo-cubic lattice cages in CH3NH3PbI3 crystals with a room temperature residence time of ∼14 ps. Free rotation, π-flips and ionic diffusion are ruled out within a 1-200-ps time window. Monte Carlo simulations of interacting CH3NH3(+) dipoles realigning within a 3D lattice suggest that the scattering measurements may be explained by the stabilization of CH3NH3(+) in either antiferroelectric or ferroelectric domains. Collective realignment of CH3NH3(+) to screen a device's built-in potential could reduce photovoltaic performance. However, we estimate the timescale for a domain wall to traverse a typical device to be ∼0.1-1 ms, faster than most observed hysteresis.
Three organic or hybrid photovoltaic technologies are compared with respect to performance and stability under the harsh regime of concentrated light. Although all three technologies show ...surprisingly high (and linear) photocurrents, and better than expected stability, no golden apples are awarded.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Stable and efficient dye‐sensitized solar cells based on water‐containing electrolytes are shown. For water contents up to 40%, no decrease in efficiency is seen. The cells are demonstrated to be ...stable for long periods of continuous illumination.This work lays a foundation for the further development of water‐based cells for commercial production.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A NIR absorbing squaraine dye has been synthesized as a sensitizer for use in dye-sensitized solar cells (DSCs). Following computational calculations, a benzcdindole moiety was selected as an ...electron-rich heterocyclic component and condensed with indole-based emisquaraine bearing a carboxyl group, as an anchor for their immobilization on TiO2, to obtain an unsymmetrical squaraine with extended absorption due to its extensive π conjugation. The cells based on this dye exhibited a spectral response in the near-infrared region over 750 nm in addition to the visible region with a light absorption edge at 900 nm. The cells showed 1.1% efficiency and Incident Photon Current Efficiency (IPCE) of 36% at 800 nm.
•Synthesis and spectroscopic characterization of an unsymmetrical NIR squaraine dye.•Structure optimization by computational analysis to extend π-conjugation.•DSCs based on TiO2 photoelectrodes were fabricated.•A 1.1% efficiency was obtained with IPCE of 36% at 800 nm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Methylammonium lead iodide (MAPI) cells of the design FTO/sTiO2/mpTiO2/MAPI/Spiro-OMeTAD/Au, where FTO is fluorine-doped tin oxide, sTiO2 indicates solid-TiO2, and mpTiO2 is mesoporous TiO2, are ...studied using transient photovoltage (TPV), differential capacitance, charge extraction, current interrupt, and chronophotoamperometry. We show that in mpTiO2/MAPI cells there are two kinds of extractable charge stored under operation: a capacitive electronic charge (∼0.2 μC/cm2) and another, larger charge (40 μC/cm2), possibly related to mobile ions. Transient photovoltage decays are strongly double exponential with two time constants that differ by a factor of ∼5, independent of bias light intensity. The fast decay (∼1 μs at 1 sun) is assigned to the predominant charge recombination pathway in the cell. We examine and reject the possibility that the fast decay is due to ferroelectric relaxation or to the bulk photovoltaic effect. Like many MAPI solar cells, the studied cells show significant J–V hysteresis. Capacitance vs open circuit voltage (V oc) data indicate that the hysteresis involves a change in internal potential gradients, likely a shift in band offset at the TiO2/MAPI interface. The TPV results show that the V oc hysteresis is not due to a change in recombination rate constant. Calculation of recombination flux at V oc suggests that the hysteresis is also not due to an increase in charge separation efficiency and that charge generation is not a function of applied bias. We also show that the J–V hysteresis is not a light driven effect but is caused by exposure to electrical bias, light or dark.
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IJS, KILJ, NUK, PNG, UL, UM
Electron transfer from TiO2 to iodine/iodide electrolytes proceeds via reduction of either I3 – or uncomplexed I2 (free iodine), but which route predominates has not previously been determined. By ...measurement of the electron lifetime while independently varying free iodine or I3 – concentrations, we find the lifetime is correlated with free-iodine concentration and independent of I3 – concentration. This trend supports the hypothesis that electron recombination to the electrolyte occurs predominantly by iodine reduction rather than reduction of triiodide.
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IJS, KILJ, NUK, PNG, UL, UM
TiO sub(2)/Z907 and TiO sub(2)/D149 films have been subjected to 1 minute heating in room air to 120 degree C, 190 degree C, and 255 degree C. Liquid electrolyte dye-sensitised solar cells (DSSCs), ...fabricated after the heating step, are used to assess the damage to the TiO sub(2)/dye film by the heat. N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) and spiro-OMeTAD (SOT) hole conductors are also melt processed onto the TiO sub(2)/dye films, requiring 190 degree C and 255 degree C respectively. The hole conductors have been removed by dissolution and liquid electrolyte DSSCs have been fabricated from the TiO sub(2)/dye films. The effect of the 120 degree C heat step is minimal. After 190 degree C heating the efficiency loss is 10-20% depending on dye and film thickness. After 255 degree C heating the efficiency loss is from 27 to 65%. The loss of efficiency occurs almost entirely due to a decrease in recombination lifetime, up to 100 fold in the worst case. This causes a decrease in V sub(oc), and also in collection efficiency for thicker films. Solid state DSSCs made with melt processed spiro-OMeTAD on 2 mu m TiO sub(2)/Z907 films are shown, with efficiency of 0.45%. Efficiency is limited by a thick capping layer and base (4-tert-butylpyridine, TBP) boil-off during processing.
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