Perovskite solar cells are one of the most promising photovoltaic technologies with their extraordinary progress in efficiency and the simple processes required to produce them. However, the frequent ...presence of a pronounced hysteresis in the current voltage characteristic of these devices arises concerns on the intrinsic stability of organo-metal halides, challenging the reliability of technology itself. Here, we show that n-doping of mesoporous TiO2 is accomplished by facile post treatment of the films with lithium salts. We demonstrate that the Li-doped TiO2 electrodes exhibit superior electronic properties, by reducing electronic trap states enabling faster electron transport. Perovskite solar cells prepared using the Li-doped films as scaffold to host the CH3NH3PbI3 light harvester produce substantially higher performances compared with undoped electrodes, improving the power conversion efficiency from 17 to over 19% with negligible hysteretic behaviour (lower than 0.3%).
The high conversion efficiency has made metal halide perovskite solar cells a real breakthrough in thin film photovoltaic technology in recent years. Here, we introduce a straightforward strategy to ...reduce the level of electronic defects present at the interface between the perovskite film and the hole transport layer by treating the perovskite surface with different types of ammonium salts, namely ethylammonium, imidazolium and guanidinium iodide. We use a triple cation perovskite formulation containing primarily formamidinium and small amounts of cesium and methylammonium. We find that this treatment boosts the power conversion efficiency from 20.5% for the control to 22.3%, 22.1%, and 21.0% for the devices treated with ethylammonium, imidazolium and guanidinium iodide, respectively. Best performing devices showed a loss in efficiency of only 5% under full sunlight intensity with maximum power tracking for 550 h. We apply 2D- solid-state NMR to unravel the atomic-level mechanism of this passivation effect.
The simplification of perovskite solar cells (PSCs), by replacing the mesoporous electron selective layer (ESL) with a planar one, is advantageous for large-scale manufacturing. PSCs with a planar ...TiO sub(2) ESL have been demonstrated, but these exhibit unstabilized power conversion efficiencies (PCEs). Herein we show that planar PSCs using TiO sub(2) are inherently limited due to conduction band misalignment and demonstrate, with a variety of characterization techniques, for the first time that SnO sub(2) achieves a barrier-free energetic configuration, obtaining almost hysteresis-free PCEs of over 18% with record high voltages of up to 1.19 V.
Solid-state dye-sensitized solar cells currently suffer from issues such as inadequate nanopore filling, low conductivity and crystallization of hole-transport materials infiltrated in the mesoscopic ...TiO
scaffolds, leading to low performances. Here we report a record 11% stable solid-state dye-sensitized solar cell under standard air mass 1.5 global using a hole-transport material composed of a blend of Cu (4,4',6,6'-tetramethyl-2,2'-bipyridine)
(bis(trifluoromethylsulfonyl)imide)
and Cu (4,4',6,6'-tetramethyl-2,2'-bipyridine)
(bis(trifluoromethylsulfonyl)imide). The amorphous Cu(II/I) conductors that conduct holes by rapid hopping infiltrated in a 6.5 μm-thick mesoscopic TiO
scaffold are crucial for achieving such high efficiency. Using time-resolved laser photolysis, we determine the time constants for electron injection from the photoexcited sensitizers Y123 into the TiO
and regeneration of the Y123 by Cu(I) to be 25 ps and 3.2 μs, respectively. Our work will foster the development of low-cost solid-state photovoltaic based on transition metal complexes as hole conductors.
Artificial photosynthesis, mimicking nature in its efforts to store solar energy, has received considerable attention from the research community. Most of these attempts target the production of H2 ...as a fuel and our group recently demonstrated solar-to-hydrogen conversion at 12.3% efficiency. Here, in an effort to take this approach closer to real photosynthesis, which is based on the conversion of CO2, we demonstrate the efficient reduction of CO2 to carbon monoxide driven solely by simulated sunlight using water as the electron source. Employing series-connected perovskite photovoltaics and high-performance catalyst electrodes, we reach a solar-to-CO efficiency exceeding 6.5%, which represents a new benchmark in sunlight-driven CO2 conversion. Considering hydrogen as a secondary product, an efficiency exceeding 7% is observed. Furthermore, this study represents one of the first demonstrations of extended, stable operation of perovskite photovoltaics, whose large open-circuit voltage is shown to be particularly suited for this process.
Ionic liquids can retard the perovskite crystallization with the aim to form compact films with larger and more uniformly distributed grain size. The ionic liquid driven crystallization is exploited ...to prepared a record planar perovskite solar cell with stabilized power output of 19.5%.
Dye-sensitized solar cells (DSSCs) have shown significant potential for indoor and building-integrated photovoltaic applications. Herein we present three new D–A−π–A organic sensitizers, XY1, XY2, ...and XY3, that exhibit high molar extinction coefficients and a broad absorption range. Molecular modifications of these dyes, featuring a benzothiadiazole (BTZ) auxiliary acceptor, were achieved by introducing a thiophene heterocycle as well as by shifting the position of BTZ on the conjugated bridge. The ensuing high molar absorption coefficients enabled the fabrication of highly efficient thin-film solid-state DSSCs with only 1.3 μm mesoporous TiO2 layer. XY2 with a molar extinction coefficient of 6.66 × 104 M–1 cm–1 at 578 nm led to the best photovoltaic performance of 7.51%.
The most commonly used redox mediators in dye-sensitized solar cells (DSCs), iodide/triiodide and cobalt trisbipyridine (Co(bpy)32+/3+), were successfully replaced by ...bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) (Cu(dmp)21+/2+). The use of the copper complex based electrolyte led to an exceptionally high photovoltaic performance of 8.3% for LEG4-sensitized TiO2 solar cells, with a remarkably high open-circuit potential of above 1.0 V at 1000 W m–2 under AM1.5G conditions. The copper complex based redox electrolyte has higher diffusion coefficients and is considerably faster in dye regeneration than comparable cobalt trisbipyridine based electrolytes. A driving force for dye regeneration of only 0.2 eV is sufficient to obtain unit yield, pointing to new possibilities for improvement in DSC efficiencies. The interaction of the excited dye with components of the electrolyte was monitored using steady-state emission measurements and time-correlated single-photon counting (TC-SPC). Our results indicate bimolecular reductive quenching of the excited LEG4 dye by the Cu(dmp)22+ complex through a dynamic mechanism. Excited-state dye molecules can readily undergo bimolecular electron transfer with a suitable donor molecule. In DSCs this process can occur when the excited dye is unable to inject electrons into the TiO2. With a high electrolyte concentration the excited dye can be intercepted with an electron from the electrolyte resulting in the reduced state of the dye. Quenching of the reduced dye by the electrolyte competes with electron injection and results in a lower photocurrent. Quenching of excited LEG4 by complexes of Cu(dmp)2+, Co(bpy)32+, and Co(bpy)33+ followed a static mechanism, due ground-state dye–quencher binding. Inhibition of unwanted quenching processes by structural modifications may open ways to further increase the overall efficiency.
We report on both the intrinsic and the extrinsic stability of a formamidinium lead bromide CH(NH2)2PbBr3 = FAPbBr3 perovskite solar cell that yields a high photovoltage. The fabrication of FAPbBr3 ...devices, displaying an outstanding photovoltage of 1.53 V and a power conversion efficiency of over 8%, was realized by modifying the mesoporous TiO2–FAPbBr3 interface using lithium treatment. Reasons for improved photovoltaic performance were revealed by a combination of techniques, including photothermal deflection absorption spectroscopy (PDS), transient-photovoltage and charge-extraction analysis, and time-integrated and time-resolved photoluminescence. With lithium-treated TiO2 films, PDS reveals that the TiO2–FAPbBr3 interface exhibits low energetic disorder, and the emission dynamics showed that electron injection from the conduction band of FAPbBr3 into that of mesoporous TiO2 is faster than for the untreated scaffold. Moreover, compared to the device with pristine TiO2, the charge carrier recombination rate within a device based on lithium-treated TiO2 film is 1 order of magnitude lower. Importantly, the operational stability of perovskites solar cells examined at a maximum power point revealed that the FAPbBr3 material is intrinsically (under nitrogen) as well as extrinsically (in ambient conditions) stable, as the unsealed devices retained over 95% of the initial efficiency under continuous full sun illumination for 150 h in nitrogen and dry air and 80% in 60% relative humidity (T = ∼60 °C). The demonstration of high photovoltage, a record for FAPbBr3, together with robust stability renders our work of practical significance.
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