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%).
CH3NH3PbX3 (MAPbX3) perovskites have attracted considerable attention as absorber materials for solar light harvesting, reaching solar to power conversion efficiencies above 20%. In spite of the ...rapid evolution of the efficiencies, the understanding of basic properties of these semiconductors is still ongoing. One phenomenon with so far unclear origin is the so-called hysteresis in the current-voltage characteristics of these solar cells. Here we investigate the origin of this phenomenon with a combined experimental and computational approach. Experimentally the activation energy for the hysteretic process is determined and compared with the computational results. First-principles simulations show that the timescale for MA(+) rotation excludes a MA-related ferroelectric effect as possible origin for the observed hysteresis. On the other hand, the computationally determined activation energies for halide ion (vacancy) migration are in excellent agreement with the experimentally determined values, suggesting that the migration of this species causes the observed hysteretic behaviour of these solar cells.
Photocathodes based on cuprous oxide (Cu2O) are promising materials for large scale and widespread solar fuel generation due to the abundance of copper, suitable bandgap, and favorable band ...alignments for reducing water and carbon dioxide. A protective overlayer is required to stabilize the Cu2O in aqueous media under illumination, and the interface between this overlayer and the catalyst nanoparticles was previously identified as a key source of instability. Here, the properties of the protective titanium dioxide overlayer of composite cuprous oxide photocathodes are further investigated, as well as an oxide‐based hydrogen evolution catalyst, ruthenium oxide (RuO2). The RuO2‐catalyzed photoelectrodes exhibit much improved stability versus platinum nanoparticles, with 94% stability after 8 h of light‐chopping chronoamperometry. Faradaic efficiencies of ∼100% are obtained as determined by measurement of the evolved hydrogen gas. The sustained photocurrents of close to 5 mA cm−2 obtained with this electrode during the chronoamperometry measurement (at 0 V vs. the reversible hydrogen electrode, pH 5, and simulated 1 sun illumination) would correspond to greater than 6% solar‐to‐hydrogen conversion efficiency in a tandem photoelectrochemical cell, where the bias is provided by a photovoltaic device such as a dye‐sensitized solar cell.
Ruthenium oxide on cuprous oxide photocathodes enhanced by a built‐in p–n junction yields an active catalyst for hydrogen generation from water and unprecedented 94% stability over 8 h of light chopping chronoamperometry at 0 V vs. the reversible hydrogen electrode. The photocurrents obtained would correspond to greater than 6% solar‐to‐hydrogen efficiency in a tandem cell configuration.
We present a systematic study on the effects of electrodeposition parameters on the photoelectrochemical properties of Cu2O. The influence of deposition variables (temperature, pH, and deposition ...current density) on conductivity has been widely explored in the past for this semiconductor, but the optimization of the electrodeposition process for the photoelectrochemical response in aqueous solutions under AM 1.5 illumination has received far less attention. In this work, we analyze the photoactivity of Cu2O films deposited at different conditions and correlate the photoresponse to morphology, film orientation, and electrical properties. The photoelectrochemical response was measured by linear sweep voltammetry under chopped simulated AM 1.5 illumination. The highest photocurrent obtained was −2.4 mA cm–2 at 0.25 V vs RHE for a film thickness of 1.3 μm. This is the highest reported value reached so far for this material in an aqueous electrolyte under AM 1.5 illumination. The optical and electrical properties of the most photoactive electrode were investigated by UV–vis spectroscopy and electrochemical impedance, while the minority carrier lifetime and diffusion length were measured by optical-pump THz-probe spectroscopy.
Photoelectrochemical water-splitting devices, which use solar energy to convert water into hydrogen and oxygen, have been investigated for decades. Multijunction designs are most efficient, as they ...can absorb enough solar energy and provide sufficient free energy for water cleavage. However, a balance exists between device complexity, cost and efficiency. Water splitters fabricated using triple-junction amorphous silicon or III-V semiconductors have demonstrated reasonable efficiencies, but at high cost and high device complexity. Simpler approaches using oxide-based semiconductors in a dual-absorber tandem approach have reported solar-to-hydrogen (STH) conversion efficiencies only up to 0.3% (ref. 4). Here, we present a device based on an oxide photoanode and a dye-sensitized solar cell, which performs unassisted water splitting with an efficiency of up to 3.1% STH. The design relies on carefully selected redox mediators for the dye-sensitized solar cell and surface passivation techniques and catalysts for the oxide-based photoanodes.
Advances in solar photovoltaics are urgently needed to increase the performance and reduce the cost of harvesting solar power. Solution-processed photovoltaics are cost-effective to manufacture and ...offer the potential for physical flexibility. Rapid progress in their development has increased their solar-power conversion efficiencies. The nanometre (electron) and micrometre (photon) scale interfaces between the crystalline domains that make up solution-processed solar cells are crucial for efficient charge transport. These interfaces include large surface area junctions between photoelectron donors and acceptors, the intralayer grain boundaries within the absorber, and the interfaces between photoactive layers and the top and bottom contacts. Controlling the collection and minimizing the trapping of charge carriers at these boundaries is crucial to efficiency.
Developing non-noble catalysts with superior activity and durability for oxygen evolution reaction (OER) in acidic media is paramount for hydrogen production from water. Still, challenges remain due ...to the inadequate activity and stability of the OER catalyst. Here, we report a cost-effective and stable manganese oxybromide (Mn
O
Br
) catalyst exhibiting an excellent OER activity in acidic electrolytes, with an overpotential of as low as 295 ± 5 mV at a current density of 10 mA cm
. Mn
O
Br
maintains good stability under operating conditions for at least 500 h. In situ Raman spectroscopy, X ray absorption near edge spectroscopy, and density functional theory calculations confirm that a self-oxidized surface with enhanced electronic transmission capacity forms on Mn
O
Br
and is responsible for both the high catalytic activity and long-term stability during catalysis. The development of Mn
O
Br
as an OER catalyst provides crucial insights into the design of non-noble metal electrocatalysts for water oxidation.
Through examination of the optoelectronic and photoelectrochemical properties of BiVO4 and Cu2O photoelectrodes, we evaluate the feasibility of a BiVO4/Cu2O photoanode/photocathode tandem cell for ...overall unassisted solar water splitting. Using state-of-the-art photoelectrodes we identify current-matching conditions by altering the photoanode active layer thickness. By further employing water oxidation and reduction catalysts (Co-Pi and RuO x , respectively) together with an operating point analysis, we show that an unassisted solar photocurrent density on the order of 1 mA cm–2 is possible in a tandem cell and moreover gain insight into routes for improvement. Finally, we demonstrate the unassisted 2-electrode operation of the tandem cell. Photocurrents corresponding to ca. 0.5% solar-to-hydrogen conversion efficiency were found to decay over the course of minutes because of the detachment of the Co-Pi catalyst. This aspect provides a fundamental challenge to the stable operation of the tandem cell with the currently employed catalysts.
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