20 research outputs found
Optically Transparent FTO-Free Cathode for Dye-Sensitized Solar Cells
The woven fabric containing electrochemically
platinized tungsten wire is an affordable flexible cathode for liquid-junction
dye-sensitized solar cells with the I<sub>3</sub><sup>ā</sup>/I<sup>ā</sup> redox mediator and electrolyte solution consisting
of ionic liquids and propionitrile. The fabric-based electrode outperforms
the thermally platinized FTO in serial ohmic resistance and charge-transfer
resistance for triiodide reduction, and it offers comparable or better
optical transparency in the visible and particularly in the near-IR
spectral region. The electrode exhibits good stability during electrochemical
loading and storage at open circuit. The dye-sensitized solar cells
with a C101-sensitized titania photoanode and either PtāW/PEN
or PtāFTO cathodes show a comparable performance
Phase Segregation in Csā, Rb- and KāDoped Mixed-Cation (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> Hybrid Perovskites from Solid-State NMR
Hybrid
(organicāinorganic) multication lead halide perovskites
hold promise for a new generation of easily processable solar cells.
Best performing compositions to date are multiple-cation solid alloys
of formamidinium (FA), methylammonium (MA), cesium, and rubidium lead
halides which provide power conversion efficiencies up to around 22%.
Here, we elucidate the atomic-level nature of Cs and Rb incorporation
into the perovskite lattice of FA-based materials. We use <sup>133</sup>Cs, <sup>87</sup>Rb, <sup>39</sup>K, <sup>13</sup>C, and <sup>14</sup>N solid-state MAS NMR to probe microscopic composition of Cs-, Rb-,
K-, MA-, and FA-containing phases in double-, triple-, and quadruple-cation
lead halides in bulk and in a thin film. Contrary to previous reports,
we have found no proof of Rb or K incorporation into the 3D perovskite
lattice in these systems. We also show that the structure of bulk
mechanochemical perovskites bears close resemblance to that of thin
films, making them a good benchmark for structural studies. These
findings provide fundamental understanding of previously reported
excellent photovoltaic parameters in these systems and their superior
stability
Phase Segregation in Potassium-Doped Lead Halide Perovskites from <sup>39</sup>K Solid-State NMR at 21.1 T
Organicāinorganic
lead halide perovskites are a promising
family of light absorbers for a new generation of solar cells, with
reported efficiencies currently exceeding 22%. A common problem of
solar cells fabricated using these materials is that their efficiency
depends on their cycling history, an effect known as currentāvoltage
(<i>J</i>ā<i>V</i>) hysteresis. Potassium
doping has recently emerged as a universal way to overcome this adverse
phenomenon. While the atomistic origins of <i>J</i>ā<i>V</i> hysteresis are still not fully understood, it is essential
to rationalize the atomic-level effect of protocols that lead to its
suppression. Here, using <sup>39</sup>K MAS NMR at 21.1 T we provide
for the first time atomic-level characterization of the potassium-containing
phases that are formed upon KI doping of multication and multianion
lead halide perovskites. We find no evidence of potassium incorporation
into 3D perovskite lattices of the recently reported materials. Instead,
we observe formation of a mixture of potassium-rich phases and unreacted
KI. In the case of Br-containing lead halide perovskites doped with
KI, a mixture of KI and KBr ensues, leading to a change in the Br/I
ratio in the perovskite phase with respect to the undoped perovskite.
Simultaneous Cs and K doping leads to the formation of nonperovskite
Cs/K lead iodide phases
Phase Segregation in Potassium-Doped Lead Halide Perovskites from <sup>39</sup>K Solid-State NMR at 21.1 T
Organicāinorganic
lead halide perovskites are a promising
family of light absorbers for a new generation of solar cells, with
reported efficiencies currently exceeding 22%. A common problem of
solar cells fabricated using these materials is that their efficiency
depends on their cycling history, an effect known as currentāvoltage
(<i>J</i>ā<i>V</i>) hysteresis. Potassium
doping has recently emerged as a universal way to overcome this adverse
phenomenon. While the atomistic origins of <i>J</i>ā<i>V</i> hysteresis are still not fully understood, it is essential
to rationalize the atomic-level effect of protocols that lead to its
suppression. Here, using <sup>39</sup>K MAS NMR at 21.1 T we provide
for the first time atomic-level characterization of the potassium-containing
phases that are formed upon KI doping of multication and multianion
lead halide perovskites. We find no evidence of potassium incorporation
into 3D perovskite lattices of the recently reported materials. Instead,
we observe formation of a mixture of potassium-rich phases and unreacted
KI. In the case of Br-containing lead halide perovskites doped with
KI, a mixture of KI and KBr ensues, leading to a change in the Br/I
ratio in the perovskite phase with respect to the undoped perovskite.
Simultaneous Cs and K doping leads to the formation of nonperovskite
Cs/K lead iodide phases
Phase Segregation in Csā, Rb- and KāDoped Mixed-Cation (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> Hybrid Perovskites from Solid-State NMR
Hybrid
(organicāinorganic) multication lead halide perovskites
hold promise for a new generation of easily processable solar cells.
Best performing compositions to date are multiple-cation solid alloys
of formamidinium (FA), methylammonium (MA), cesium, and rubidium lead
halides which provide power conversion efficiencies up to around 22%.
Here, we elucidate the atomic-level nature of Cs and Rb incorporation
into the perovskite lattice of FA-based materials. We use <sup>133</sup>Cs, <sup>87</sup>Rb, <sup>39</sup>K, <sup>13</sup>C, and <sup>14</sup>N solid-state MAS NMR to probe microscopic composition of Cs-, Rb-,
K-, MA-, and FA-containing phases in double-, triple-, and quadruple-cation
lead halides in bulk and in a thin film. Contrary to previous reports,
we have found no proof of Rb or K incorporation into the 3D perovskite
lattice in these systems. We also show that the structure of bulk
mechanochemical perovskites bears close resemblance to that of thin
films, making them a good benchmark for structural studies. These
findings provide fundamental understanding of previously reported
excellent photovoltaic parameters in these systems and their superior
stability
Reduction in the Interfacial Trap Density of Mechanochemically Synthesized MAPbI<sub>3</sub>
Organo-lead
halide perovskites have emerged as promising light harvesting materials
for solar cells. The ability to prepare high quality films with a
low concentration of defects is essential for obtaining high device
performance. Here, we advance the procedure for the fabrication of
efficient perovskite solar cells (PSCs) based on mechanochemically
synthesized MAPbI<sub>3</sub>. The use of mechano-perovskite for the
thin film formation provides a high degree of control of the stoichiometry
and allows for the growth of relatively large crystalline grains.
The best device achieved a maximum PCE of 17.5% from a currentāvoltage
scan (<i>JāV</i>), which stabilized at 16.8% after
60 s of maximum power point tracking. Strikingly, PSCs based on MAPbI<sub>3</sub> mechanoperovskite exhibit lower āhystereticā
behavior in comparison to that comprising MAPbI<sub>3</sub> obtained
from the conventional solvothermal reaction between PbI<sub>2</sub> and MAI. To gain a better understanding of the difference in <i>JāV</i> hysteresis, we analyze the charge/ion accumulation
mechanism and identify the defect energy distribution in the resulting
MAPbI<sub>3</sub> based devices. These results indicate that the use
of mechanochemically synthesized perovskites provides a promising
strategy for the formation of crystalline films demonstrating slow
charge recombination and low trap density
Cation Dynamics in Mixed-Cation (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> Hybrid Perovskites from Solid-State NMR
Mixed-cation
organic lead halide perovskites attract unfaltering
attention owing to their excellent photovoltaic properties. Currently,
the best performing perovskite materials contain multiple cations
and provide power conversion efficiencies up to around 22%. Here,
we report the first quantitative, cation-specific data on cation reorientation
dynamics in hybrid mixed-cation formamidinium (FA)/methylammonium
(MA) lead halide perovskites. We use <sup>14</sup>N, <sup>2</sup>H, <sup>13</sup>C, and <sup>1</sup>H solid-state MAS NMR to elucidate cation
reorientation dynamics, microscopic phase composition, and the MA/FA
ratio, in (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> between 100 and 330 K. The reorientation
rates correlate in a striking manner with the carrier lifetimes previously
reported for these materials and provide evidence of the polaronic
nature of charge carriers in PV perovskites
Cation Dynamics in Mixed-Cation (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> Hybrid Perovskites from Solid-State NMR
Mixed-cation
organic lead halide perovskites attract unfaltering
attention owing to their excellent photovoltaic properties. Currently,
the best performing perovskite materials contain multiple cations
and provide power conversion efficiencies up to around 22%. Here,
we report the first quantitative, cation-specific data on cation reorientation
dynamics in hybrid mixed-cation formamidinium (FA)/methylammonium
(MA) lead halide perovskites. We use <sup>14</sup>N, <sup>2</sup>H, <sup>13</sup>C, and <sup>1</sup>H solid-state MAS NMR to elucidate cation
reorientation dynamics, microscopic phase composition, and the MA/FA
ratio, in (MA)<sub><i>x</i></sub>(FA)<sub>1ā<i>x</i></sub>PbI<sub>3</sub> between 100 and 330 K. The reorientation
rates correlate in a striking manner with the carrier lifetimes previously
reported for these materials and provide evidence of the polaronic
nature of charge carriers in PV perovskites
Effect of Extended ĻāConjugation of the Donor Structure of Organic DāAāĻāA Dyes on the Photovoltaic Performance of Dye-Sensitized Solar Cells
Two new DāAāĻ-spacerāA organic dyes, <b>KM-10</b> and <b>KM-11</b>, containing a benzothiadiazole unit in a Ļ-spacer and a cyanoacrylic acid as an acceptor have been synthesized and tested as sensitizers in dye-sensitized solar cells. Structural variations of the donor moiety, i.e., Ļ-extension of the diphenylamine electron-donating groups, gave rise to different photovoltaic efficienciesīø7.1% for KM-10 and 8% for KM-11īødespite having comparable absorption properties. A detailed investigation, including transient photocurrent and photovoltage decay measurement, transient absorption spectroscopy, and quantum chemical methods, provided important conclusions about the nature of the substitution on the photovoltaic properties of dyes
Effect of Cs-Incorporated NiO<sub><i>x</i></sub> on the Performance of Perovskite Solar Cells
The effect of Cs-incorporated NiO<sub><i>x</i></sub> on
perovskite solar cells with an inverted structure was investigated,
where NiO<sub><i>x</i></sub> and PCBM were used as selective
contacts for holes and electrons, respectively. It was found that
the generation of an Ni phase in an NiO<sub><i>x</i></sub> layer was significantly suppressed by employing cesium. Furthermore,
Cs-incorporated NiO<sub><i>x</i></sub> enabled holes to
be efficiently separated at the interface, showing the improved photoluminescent
quenching and thus generating higher short-circuit current. The effect
of Cs incorporation was also prominent in the inhibition of recombination.
The recombination resistance of Cs-incorporated NiO<sub><i>x</i></sub> was noticeably increased by more than three-fold near the
maximum power point, leading to a higher fill factor of 0.78 and consequently
a higher power conversion efficiency of 17.2% for the device employing
Cs-incorporated NiO<sub><i>x</i></sub>