How Transparent Oxides Gain Some Color: Discovery of a CeNiO Reduced Bandgap Phase As an Absorber for Photovoltaics.

In this work, we describe the formation of a reduced bandgap CeNiO phase, which, to our knowledge, has not been previously reported, and we show how it is utilized as an absorber layer in a photovoltaic cell. The CeNiO phase is prepared by a combinatorial materials science approach, where a library containing a continuous compositional spread of Ce NiO is formed by pulsed laser deposition (PLD); a method that has not been used in the past to form Ce-Ni-O materials. The library displays a reduced bandgap throughout, calculated to be 1.

Process-Function Data Mining for the Discovery of Solid-State Iron-Oxide PV.

Data mining tools have been known to be useful for analyzing large material data sets generated by high-throughput methods. Typically, the descriptors used for the analysis are structural descriptors, which can be difficult to obtain and to tune according to the results of the analysis. In this Research Article, we show the use of deposition process parameters as descriptors for analysis of a photovoltaics data set.

A combined computational and experimental investigation of Mg doped α-Fe2O3.

In the current work, pristine α-Fe2O3 metal oxide was doped with Mg in an attempt to modulate its electronic properties. To this end, we employed an experimental high throughput strategy, including scanning XRD and optical spectroscopy, which were complimented by atomistic density functional theory (DFT) calculations. The combined study reveals that at Mg/Fe atomic ratios up to ∼1/3, the bandgaps of the hematite-Mg composite materials are similar to that of the pure material.

Open circuit potential build-up in perovskite solar cells from dark conditions to 1 sun.

The high open-circuit potential (Voc) achieved by perovskite solar cells (PSCs) is one of the keys to their success. The Voc analysis is essential to understand their working mechanisms. A large number of CH3NH3PbI3-xClx PSCs were fabricated on single large-area substrates and their Voc dependencies on illumination intensity, I0, were measured showing three distinctive regions.

Data Mining and Machine Learning Tools for Combinatorial Material Science of All-Oxide Photovoltaic Cells.

Growth in energy demands, coupled with the need for clean energy, are likely to make solar cells an important part of future energy resources. In particular, cells entirely made of metal oxides (MOs) have the potential to provide clean and affordable energy if their power conversion efficiencies are improved. Such improvements require the development of new MOs which could benefit from combining combinatorial material sciences for producing solar cells libraries with data mining tools to direct synthesis efforts.

Utilizing pulsed laser deposition lateral inhomogeneity as a tool in combinatorial material science.

Pulsed laser deposition (PLD) is widely used in combinatorial material science, as it enables rapid fabrication of different composite materials. Nevertheless, this method was usually limited to small substrates, since PLD deposition on large substrate areas results in severe lateral inhomogeneity. A few technical solutions for this problem have been suggested, including the use of different designs of masks, which were meant to prevent inhomogeneity in the thickness, density, and oxidation state of a layer, while only the composition is allowed to be changed.

Four-point probe electrical resistivity scanning system for large area conductivity and activation energy mapping.

The electrical properties of metal oxides play a crucial role in the development of new photovoltaic (PV) systems. Here we demonstrate a general approach for the determination and analysis of these properties in thin films of new metal oxide based PV materials. A high throughput electrical scanning system, which facilitates temperature dependent measurements at different atmospheres for highly resistive samples, was designed and constructed.

Quantum efficiency and bandgap analysis for combinatorial photovoltaics: sorting activity of Cu-O compounds in all-oxide device libraries.

All-oxide-based photovoltaics (PVs) encompass the potential for extremely low cost solar cells, provided they can obtain an order of magnitude improvement in their power conversion efficiencies. To achieve this goal, we perform a combinatorial materials study of metal oxide based light absorbers, charge transporters, junctions between them, and PV devices. Here we report the development of a combinatorial internal quantum efficiency (IQE) method.

Interpretation of optoelectronic transient and charge extraction measurements in dye-sensitized solar cells.

Tools that assess the limitations of dye sensitized solar cells (DSSCs) made with new materials are critical for progress. Measuring the transient electrical signals (voltage or current) after optically perturbing a DSSC is an approach which can give information about electron concentration, transport and recombination. Here we describe the theory and practice of this class of optoelectronic measurements, illustrated with numerous examples.

All-Oxide Photovoltaics.

Recently, a new field in photovoltaics (PV) has emerged, focusing on solar cells that are entirely based on metal oxide semiconductors. The all-oxide PV approach is very attractive due to the chemical stability, nontoxicity, and abundance of many metal oxides that potentially allow manufacturing under ambient conditions. Already today, metal oxides (MOs) are widely used as components in PV cells such as transparent conducting front electrodes or electron-transport layers, while only very few MOs have been used as light absorbers.

New insight into the regeneration kinetics of organic dye sensitised solar cells.

The order of regeneration for DSCs based on two organic dyes has been investigated by transient absorption spectroscopy on devices under operating conditions and determined to be 2nd order in iodide. The results shed light on the mechanism and limits to the regeneration rate relative to oxidation potential.

Simulation and measurement of complete dye sensitised solar cells: including the influence of trapping, electrolyte, oxidised dyes and light intensity on steady state and transient device behaviour.

A numerical model of the dye sensitised solar cell (DSSC) is used to assess the importance of different loss pathways under various operational conditions. Based on our current understanding, the simulation describes the processes of injection, regeneration, recombination and transport of electrons, oxidised dye molecules and electrolyte within complete devices to give both time dependent and independent descriptions of performance. The results indicate that the flux of electrons lost from the nanocrystalline TiO(2) film is typically at least twice as large under conditions equivalent to 1 sun relative to dark conditions at matched TiO(2) charge concentration.

Factors controlling charge recombination under dark and light conditions in dye sensitised solar cells.

A simple and powerful approach for assessing the recombination losses in dye sensitised solar cells (DSSCs) across the current voltage curve (j-V) as a function of TiO(2) electron concentration (n) is demonstrated. The total flux of electrons recombining with iodine species in the electrolyte and oxidised dye molecules can be thought of as a recombination current density, defined as j(rec) = j(inj)-j where j(inj) is the current of electrons injected from optically excited dye states and j is the current density collected at cell voltage (V). The electron concentration at any given operating conditions is determined by charge extraction.

Re-evaluation of recombination losses in dye-sensitized cells: the failure of dynamic relaxation methods to correctly predict diffusion length in nanoporous photoelectrodes.

Photocurrents generated by thick, strongly absorbing, dye-sensitized cells were reduced when the electrolyte iodine concentration was increased. Electron diffusion lengths measured using common transient techniques (L(n)) were at least two times higher than diffusion lengths measured at steady state (L(IPCE)). Charge collection efficiency calculated using L(n) seriously overpredicted photocurrent, while L(IPCE) correctly predicted photocurrent.

Structure/function relationships in dyes for solar energy conversion: a two-atom change in dye structure and the mechanism for its effect on cell voltage.

Recombination between injected electrons and iodine limits the photovoltage in dye-sensitized solar cells (DSSCs). We have recently suggested that many new dye molecules, intended to improve DSSCs, can accelerate this reaction, negating the expected improvement (J. Am.