Trystan Watson

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.

Perovskite processing for photovoltaics: a spectro-thermal evaluation

Thermal analysis (TGA and DSC), coupled with evolved gas FTIR spectroscopy, has been used to study the changes occurring during, and differences between materials after, the annealing step of mixed-halide methylammonium lead halide perovskites. This is important because, to date, the material is the most efficient light harvester in highly efficient, 3rd generation perovskite photovoltaic devices, and processing plays a significant role in device performance. TGA-FTIR data show only solvent evolution during the annealing step, whilst post-annealing analysis shows that the resulting material still contains a significant amount of residual solvent; however, efficient DMF removal was possible using a silica gel desiccant for a period of 3 days. The data also show that methylammonium halide decomposition does not occur until temperatures well above those used for perovskite processing, suggesting that this is not a significant issue for device manufacture. The absence of a well-defined, reversible tetragonal – cubic phase change around 55 °C in the DSC data of the annealed material, and the presence of HCl in evolved gas analysed following thermal decomposition, demonstrates that CH3NH3I3−xClx does retain some Cl after annealing and does not simply form stoichiometric CH3NH3PbI3 as has been suggested by some workers.

Ultrafast near-infrared sintering of a slot-die coated nano-silver conducting ink

Drying and sintering conductive inks for plastic electronics currently limits the rate of their roll-to-roll manufacture. Near infrared radiation is demonstrated to drastically reduce this process time, achieving conduction under 0.03 Ω per □ in 2 seconds compared to conventional hot-air oven (600 seconds) and infrared methods (84 seconds).

Rapid, continuous in situ monitoring of dye sensitisation in dye-sensitized solar cells

Two alternative techniques to the traditional dye desorption method are presented which enable rapid, continuous in situ measurement of dye uptake in porous TiO2 films used in dye-sensitized solar cells (DSC). Measurement of dye uptake is crucial for the rapid up-scaling of DSC technology since currently this is a rate limiting process step typically taking hours to achieve. Most reported measurements of dye sorption have involved desorbing dye at set intervals using a base (e.g.NaOH) followed by UV-vis spectroscopy. Whilst this method is accurate and quantitative, it is time-consuming, destructive of the devices and in situ measurements are impossible. The latter are important as dyeing speeds increase. Here we present two methods to measure the temporal evolution of colour at the interface of porous TiO2 films with TCO-coated glass. The first method uses digital image capture and subsequent image analysis to extract RGB (red-green-blue) colour data enabling a rapid quantification of dye uptake over periods from seconds to hours. The second method uses UV-visible reflectance spectroscopy providing more highly resolved wavelength data; important as DSC co-sensitisation is becoming increasingly important. There is a clear correlation between the two in situ methods reported here as well as with traditional dye desorption methods for measurements made over a period of hours. These methods represent important new tools for the development of ultra-fast dye sensitisation for DSC.

Ultra-fast sintered TiO2 films in dye-sensitized solar cells: phase variation, electron transport and recombination

With the application of near-infrared radiation (NIR), TiO2 films for dye-sensitized solar cells (DSCs) on metallic substrates can be sintered in just 12.5 seconds. The photovoltaic performance of devices made with NIR sintered films match those devices made with conventionally sintered films prepared by heating for 1800 seconds. Here we characterise the electron transport, electron lifetime and phase-morphological properties of ultrafast NIR sintered films, using impedance spectroscopy, transient photovoltage decay and X-ray diffraction measurements. An important factor in NIR processing of TiO2 films is the peak metal temperature (PMT) and we show that during the 12.5 second heat treatment, a PMT of around 635 °C gives near identical electron transport, electron lifetime and morphological properties, as well comparable photovoltaic performance to a conventionally sintered (500 °C, 30 min) film. We demonstrate that the rapid heating of the TiO2 (to temperatures of up to 785 °C) does not lead to a large scale rutile phase transition. As such photovoltaic performance of resultant DSC devices is maintained since the heating period is insufficient to induce a significant transition from anatase to rutile or morphology changes which result in a loss of photocurrent.

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.

Flexographic printing of graphene nanoplatelet ink to replace platinum as counter electrode catalyst in flexible dye sensitised solar cell

Abstract A semitransparent catalytically active graphene nanoplatelet (GNP) ink was developed suitable for roll to roll printing onto a flexible indium tin oxide substrate at a speed of 0·4 m s−1. Dye sensitised solar cells using this ink as a catalyst demonstrated efficiencies of 2·0%, compared with 2·6% for sputtered platinum. Given further optimisation, GNP inks have the potential to replace chemically reduced or sputtered platinum. This would have the benefit of replacing the chemical reduction or sputtering operations as well as providing potential material cost benefits.

Performance enhancement of solution processed perovskite solar cells incorporating functionalized silica nanoparticles

High efficiency, solution processed organic–inorganic trihalide perovskite solar cells are now a reality, meaning that perovskite photovoltaics have the potential to challenge more established photovoltaic technologies. To date, some of the most efficient solution processed perovskite solar cells feature a pre-deposited Al2O3 scaffold and we have shown in a previous communication, that it is possible to make efficient devices by co-depositing the Al2O3 nanoparticles with the perovskite precursor solution. In this work, we have substituted the alumina nanoparticles with 3-aminopropyl (3-oxobutanoic acid) functionalized silica nanoparticles (f-SiO2). We observe performance enhancements in planar heterojunction (PHJ) devices made with up to 0.75 wt% f-SiO2 nanoparticles present in the precursor solution, yielding power conversion efficiencies (PCE) of up to 12.4%, compared to the maximum PCE of 10.5% in the equivalent PHJ devices made without f-SiO2 nanoparticles. The performance enhancement arises in part from an average increase to VOC by up to 50 mV when the nanoparticles are present in the precursor solution and is attributed to substrate passivation within pinholes formed in the perovskite film during processing.