Perovskite Thin Films for Photovoltaics & Electronics

For many years organic photovoltaics (OPV) and dye-sensitised solar cells (DSSC) were leading candidates to provide low-cost, flexible solar power generation. A key development came from this community with the first reports of "perovskite" solar cells by several pioneering research groups using processing technology similar to OPVs, but replacing the active layer with a crystalline "perovskite" material which showed a step-change in performance - both in terms of how much light it could absorb, but also how easily the electricity could be extracted. Within just a few years efficiencies were above 20%, continuing on an upwards trend to the >25% records today. For the first time a technology exists which can rival Silicon for solar conversion efficiency, but with much simpler, cheaper processing requirements. Commercialization of the technology is imminent, less than a decade after the initial discovery.

Though less mature, a wider field of "Perovskite electronics" is beginning to emerge, with the materials also finding potentially exciting uses in LEDs, transistors and lasers amongst other devices.

Kurt J. Lesker has been manufacturing PVD tools for perovskite research since the inception of the technology, having supplied many tools to leading research institutions globally. Because of this, our team of dedicated applications, design and vacuum experts have developed unrivalled know-how about the production of perovskite thin film systems to meet the stringent demands of this research community.

Vacuum evaporation of perovskite layers can be challenging due to some unique processing requirements. The perovskite layer cannot be evaporated as-is, rather it is formed in-situ on the substrate surface after thermal co-evaporation of at least two precursor materials. For example, the formation of Methylammonium Lead Iodide (MAPI) is typically performed through the controlled evaporation and conversion of Lead Iodide (PbI2) and Methylammonium Iodide (MAI). Formamidinium Iodide (FAI) is another popular precursor used today with other metal halides.

There is an inherent requirement to control multiple sources simultaneously with the same high level of accuracy but with no crosstalk or cross-contamination. Additionally, certain precursors evaporate at very low temperatures, so special sources are required which are optimised for this reduced temperature range.

Kurt J. Lesker has worked with many partners over the years to refine our design for perovskite thin film tools. We understand that materials such as MAI provide a number of challenges for deposition, in particular their extremely high vapour pressure during evaporation which means they typically form a vapour "cloud" rather than a typical evaporation plume, and this can not only make control difficult but can also cause significant material cross-contamination. Highly accurate PID source control is required. Cross-contamination and re-evaporation can be limited using cooling shrouds in the system, though KJLC recommend isolating the perovskite process to a dedicated chamber when producing complete device stacks by using a glovebox-connected multi-chamber layout.

We also know that perovskite precursors can cause corrosion of vacuum system components, particularly where they may be exposed to moisture, and this must be accounted for in the system design. The high vacuum pump must be protected by a cooled baffle at the entry port, and for turbo-pumped systems a sealing gas flow is used across the bearings to extend lifetime or else the pump will fail. The internal chamber components and walls are protected by operating in a glovebox environment, however nickel-plating or stainless steel can be used dependent on the tool specification.

We understand that tool personalization that addresses a researcher's unique requirements is critically important and we have therefore developed and support an extensive capabilities portfolio including:

• Low Temperature Evaporation LTE sources with unique plug-in base for easy swap-out designed for effective deposition of volatile perovskite and metal halide precursors in the range of 50-600°C
• Rapid source cooling using water-cooled HydraVap™ evaporation sources
• Industry-leading evaporation rate reading and PID control for accurate film deposition
• Co-deposition as standard to produce complex and precise blended layers of perovskite and metal halide
• Shadow mask capability with in-situ mechanical transfer is available on larger systems for production of complex device structures
• Cooled source shroud limits contamination and re-evaporation of high vapour pressure materials such as MAI
• All perovskite tools are provided with a "Lesker Perovskite Pumping Kit" to prevent harmful corrosion of the turbo pump which will fail if not fitted
• Nickel-plated or stainless-steel chamber options are available where internal corrosion is a concern
• Heating and cooling substrate platens up to 200mm x 200mm
• RF bias for cleaning of substrates prior to deposition
• Space-optimised process chamber geometries to allow maximal source count possibilities for high throughput materials research or complex multi-layer stack structures
• In-situ film measurement to accurately monitor real-time deposition parameters
• Process chamber shielding to ensure minimal crosstalk between each deposition source and quartz crystal monitors
• Load lock chambers to reduce takt time and increase productivity
• Cluster tool options with multi-chambers for high throughput and complex device structures with either in-vacuum transfer or transfer through a glovebox
• Glovebox compatibility as standard for handling of sensitive materials and devices
• Glovebox-connected, multi-chamber configurations available to separate the perovskite process from other high-power sources such as thermal evaporation (metals) or sputtering (metals and oxides)
• Glovebox options including robot encapsulation, spin-coater, hot-plate, UV cure and solar simulator
• Fully integrated film recipe and system control using our Lesker eKLipse™ process control platform for precise, repeatable deposition conditions

We want to hear from you. Our thin film experts and service support team are eager to help enable your important research.