Joel Troughton

A Transparent Conductive Adhesive Laminate Electrode for High‐Efficiency Organic‐Inorganic Lead Halide Perovskite Solar Cells

A self-adhesive laminate solar-cell electrode is presented based on a metal grid embedded in a polymer film (x-y conduction) and set in contact with the active layer using a pressure-sensitive adhesive containing a very low quantity (1.8%) of organic conductor, which self-organizes to provide z conduction to the grid. This ITO-free material performs in an identical fashion to evaporated gold in high-efficiency perovskite solar cells.

Efficient, Semitransparent Neutral-Colored Solar Cells Based on Microstructured Formamidinium Lead Trihalide Perovskite

Efficient, neutral-colored semitransparent solar cells are of commercial interest for incorporation into the windows and surfaces of buildings and automobiles. Here, we report on semitransparent perovskite solar cells that are both efficient and neutral-colored, even in full working devices. Using the microstructured architecture previously developed, we achieve higher efficiencies by replacing methylammonium lead iodide perovskite with formamidinium lead iodide. Current-voltage hysteresis is also much reduced. Furthermore, we apply a novel transparent cathode to the devices, enabling us to fabricate neutral-colored semitransparent full solar cells for the first time. Such devices demonstrate over 5% power conversion efficiency for average visible transparencies of almost 30%, retaining impressive color-neutrality. This makes these devices the best-performing single-junction neutral-colored semitransparent solar cells to date. These microstructured perovskite solar cells are shown to have a significant advantage over silicon solar cells in terms of performance at high incident angles of sunlight, making them ideal for building integration.

Highly efficient, flexible, indium-free perovskite solar cells employing metallic substrates

Flexible perovskite solar cells with power conversion efficiencies of up to 10.3% have been prepared using titanium foil as an electrode substrate. Our method uses an indium-free transparent counter electrode which allows device performance to remain high despite repeated bending, making it suitable for roll-to-roll processing.

Rapid processing of perovskite solar cells in under 2.5 seconds

A rapid annealing technique for CH3NH3PbI3 perovskite solar cells is presented. We report a co-deposited Al2O3–perovskite device annealed in under 2.5 seconds with a PCE of 10.0% compared to 10.9% for a 45 minute oven-annealed device.

Azetidinium lead iodide for perovskite solar cells

Hybrid organic–inorganic perovskites have been established as good candidate materials for emerging photovoltaics, with device efficiencies of over 22% being reported. There are currently only two organic cations, methylammonium and formamidinium, which produce 3D perovskites with band gaps suitable for photovoltaic devices. Numerous computational studies have identified azetidinium as a potential third cation for synthesizing organic–inorganic perovskites, but to date no experimental reports of azetidinium containing perovskites have been published. Here we prepare azetidinium lead iodide for the first time. Azetidinium lead iodide is a stable, bright orange material which does not appear to form a 3D or a 2D perovskite. It was successfully used as the absorber layer in solar cells. We also show that it is possible to make mixed cation devices by adding the azetidinium cation to methylammonium lead iodide. Computational studies show that the substitution of up to 5% azetidinium into the methylammonium lead iodide is energetically favourable and that phase separation does not occur at these concentrations. Mixed azetidinium–methylammonium cells show improved performance and reduced hysteresis compared to methylammonium lead iodide cells.

Compositions, colours and efficiencies of organic–inorganic lead iodide/bromide perovskites for solar cells

Abstract Developments in the field of organic–inorganic lead halide perovskite based solar cells have metaphorically opened the door to an exciting new solid state photovoltaic technology that retains the low cost and processability benefits of dye sensitised solar cells (DSCs). Encouraging device efficiencies of greater than 10% on both titania and alumina, and as a planar device, have been reported in the literature. Here we report the characteristics of a series of lead iodide/bromide perovskites. As one might expect, changing the halide(s) alters the crystal structure and band gap of the perovskite which results in the possibility of vivid and colourful solar cells; a characteristic which is seen as one of the main benefits of DSCs. X-ray diffraction and scanning electron microscopy with elemental mapping via energy dispersive X-ray analysis has been used to characterise perovskites on sensitised thin films. UV-vis and diffuse reflectance has been used to study the optical characteristics of crystallised perovskite thin films. Finally device performance is evaluated and suitability for use in photovoltaic devices is discussed.

Enhancing the stability of organolead halide perovskite films through polymer encapsulation

Perovskite solar cells based on organolead halides such as CH3NH3PbX3 (X = Cl, Br, and I) have rapidly established themselves as the frontrunners among emerging photovoltaic technologies. However, their commercial application has been hindered to date in part due to their susceptibility to degradation by UV radiation or heat in the presence of moisture. Herein we investigate the relationship between the physical properties of several polymer encapsulants (poly(methylmethacrylate) (PMMA), ethyl cellulose, polycarbonate and poly(4-methyl-1-pentene)) and their ability to function as barrier layers to improve the stability of CH3NH3PbI3−xClx films under prolonged thermal degradation at 60 °C, 80 °C and 100 °C. In all cases, polymer-coated CH3NH3PbI3−xClx films showed retarded thermal degradation compared to the uncoated films, as indicated by the quantitative decay of the perovskite band edge in the UV/Vis absorption spectrum and the appearance of PbI2 peaks in the powder X-ray diffraction pattern. However, the extent of this reduction was highly dependent on the physical properties of the polymer encapsulant. Notably, PMMA-coated CH3NH3PbI3−xClx films showed no visible signs of degradation to PbI2 after extended heating at 60 °C. However, concomitant studies by epifluorescence microscopy (FM) revealed deterioration of the CH3NH3PbI3−xClx film quality, even in the presence of a polymer-coating, at much shorter heating times (29 h), as evidenced by quenching of the film fluorescence, which was attributed to grain aggregation and the formation of associated non-radiative trap sites. Since grain aggregation occurs on a shorter timescale than chemical degradation to PbI2, this may be the limiting factor in determining the resistance of organolead halide perovskite films to thermal degradation.

Simple 3,6-bis(diphenylaminyl)carbazole molecular glasses as hole transporting materials for hybrid perovskite solar cells

Abstract3,6-bis(diphenylaminyl)carbazole molecular glasses were initially designed as solid hole conductor for solid-state dye-sensitized solar cells. Herein we employed these simple and easy-to-synthesize carbazole derivatives in CH3NH3PbI3 regular perovskite solar cells. Devices using these hole transporting materials (HTM) gave comparable efficiency to the conventional Spiro-OMeTAD based control device made under the same conditions, thus demonstrating the huge potential of carbazole-based molecular glasses as an emerging class of lower cost organic hole conductors with easier synthetic pathways for solid state hybrid solar cells.

Identifying recombination mechanisms through materials development in perovskite solar cells

Through materials and device developments and by using measurements such as transient photovoltage decay and impedance spectroscopy we have begun to identify recombination mechanisms in perovskite solar cells. At the forefront of our developments is a transparent, indium free, cathode which allows measurements to be made whilst illuminating from both the photoanode side and the cathode side of the device. Recombination is consistently faster when illuminated from the cathode side and we conclude that in this case, as charge carriers are generated closer to the perovskite/SPIRO-OMeTAD interface, interfacial recombination is a significant contributor to voltage losses within the device.

Strategies for high current densities in non-fullerene acceptors based organic solar cells

Here, we report the strategies to increase the photon harvesting in single junction organic photovoltaics by band gap engineering. Low band-gap non-fulllerene small molecule acceptors yield remarkable short-circuit current (26.6 mA/cm2) which comparable to existing high efficiency photovoltaic technologies.