can be produced via RF sputtering, [ 8a ] spray pyrolysis, [ 6a ] chemical vapor deposition [ 11 ] or electrodeposition techniques. [ 12 ] Here we investigate, for the fi rst time, Co 3 O 4 as an MO semiconductor light absorber for all-oxide PV cells. Thin fi lm heterojunction cells, [ 13 ] based on a compact TiO 2 layer produced by spray pyrolysis onto a fl uorine-doped tin oxide (FTO) substrate, followed by pulsed laser deposition of Co 3 O 4 , were investigated as a function of both their layer thicknesses and the Co 3 O 4 deposition temperature. To do this in an effi cient way, combinatorial device libraries [ 14 ] were produced with a thickness gradient ( Figure 1 d). An array of 169 round metal back-contacts, defi ning the cells, were deposited onto the library, allowing for PV performance characterization via automated high throughput methods. [ 15 ] We show that the pulsed laser deposition temperatures of the Co 3 O 4 absorber have a strong impact on device performance due to improved crystallinity and morphology. The library approach proved to be an effi cient method for determining the optimal layer thicknesses; the best performing cells (maximum power) were selected from each library created. Co 3 O 4 is investigated as a light absorber for all-oxide thin-fi lm photovoltaic cells because of its nearly ideal optical bandgap of around 1.5 eV. Thin fi lm TiO 2 /Co 3 O 4 heterojunctions are produced by spray pyrolysis of TiO 2 as a window layer, followed by pulsed laser deposition of Co 3 O 4 as a light absorbing layer. The photovoltaic performance is investigated as a function of the Co 3 O 4 deposition temperature and a direct correlation is found. The deposition temperature seems to affect both the crystallinity and the morphology of the absorber, which affects device performance. A maximum power of 22.7 µW cm −2 is obtained at the highest deposition temperature (600 °C)with an open circuit photovoltage of 430 mV and a short circuit photocurrent density of 0.2 mA cm −2 . Performing deposition at 600 °C instead of room temperature improves power by an order of magnitude and reduces the tail states (Urbach edge energy). These phenomena can be explained by larger grains that grows at high temperature, as opposed to many nucleation events that occur at lower temperature.

Here we present a comprehensive investigation of TiO2-Cu2O hetero-junction solar cells with different back contacts (Au, ITO, Cu or Ag). Combinatorial hetero-junction libraries consisting of a linear TiO2 thickness gradient produced by spray pyrolysis and a bell shaped Cu2O profile synthesized by pulsed laser deposition were chosen to investigate the impact of the two metal oxide layer thicknesses. The back contacts were deposited as round patches onto a grid of 13 × 13 points, 169 contacts for each contact material, forming a library containing 4 × 13 × 13 = 676 back contacts. Each back contact represented a solar cell with an individual TiO2 and Cu2O thickness. I-V measurements show that all four materials provide an ohmic contact and that the open circuit voltage of ∼300 mV is rather independent of both layer thicknesses and contact material. The size of the Cu2O crystals drastically decreases with distance from the center of deposition, which leads to a drastic increase of series resistance when the crystal size is <50 nm.

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. The observed bandgaps are rationalized by electronic band structure and density of states calculations. Additional rationale for the similar bandgaps in pure and doped hematite is provided by topological Bader charge analyses, which indicate that the Mg and Fe ions in the hematite matrix have similar partial atomic charges. Nonetheless, the small charge density difference between the Mg and Fe ions induces a slight spin polarization on both oxygen and Fe ions, resulting in changes in the band edges. Further charge density analyses, using charge density maps and chemical-bonding analyses with the crystal orbital Hamiltonian population scheme, indicate that Mg forms ionic bonds with the neighboring oxygen atoms. This change from iron-oxygen covalent bonds to a more ionic nature for magnesium-oxygen bonds is probably responsible for the reduction observed in the computed bulk modulus of α-Mg(0.17)Fe(1.83)O3 (193 GPa) compared to α-Fe2O3 (202 GPa).

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