Plasma CVD process shows potential for large area perovskite photovoltaics

Significance 

The application and demand for atmospheric pressure technological plasmas has increased significantly in recent years. Generally, such non-equilibrium low temperature plasmas have broad potential for application including thin film deposition and surface modification. This includes the large-scale commercial treatment of polymers to improve wettability and adhesion. The incorporation of plasma activation into an atmospheric pressure chemical vapour deposition (CVD) process enables the growth of thin films at significantly reduced substrate temperatures, offering the potential for low cost continuous deposition over large area and thermally sensitive substrates.

To date, the application of this promising technology to the production of functional inorganic materials has been limited due to compromised film properties compared to established vacuum-based processes. It is generally considered that instability and localized filaments, typical of a barrier discharge plasma operating at atmospheric pressure, could be a major factor resulting in inhomogeneous growth, pinholes and substrate damage. The generation of diffuse barrier discharges using commodity gasses at atmospheric pressure is the subject of much research with various approaches, such as audio frequency, modulated RF and pulsed DC described in the literature.

Dr. John Hodgkinson and Dr. Heather Yates from the University of Salford have recently demonstrated a bespoke roll-to-roll atmospheric pressure plasma enhanced CVD (AP PECVD) process for the production of TiO2-x over large areas at near ambient temperatures. Working in collaboration with a team of leading researchers at Centre Suisse d’Electronique et de Microtechnique (Dr. Arnaud Walter, Dr. Davide Sacchetto, Dr. Soo-Jin Moon and Dr. Sylvain Nicolay) they investigated the viability of the AP PECVD TiO2-x films as electron transport layers (ETL) in perovskite solar cells. Critically, to provide satisfactory charge separation and minimize series resistance, the ETL must be thin (sub 100 nm) compact, conformal and pinhole free. Whilst representing a considerable challenge, an atmospheric pressure process for the in-line deposition of ELT would be highly complementary to the online production of the transparent electrode, supporting the cost effective implementation of the highly promising perovskite technology. Their study is published in the research journal, Journal of Materials Chemistry C.

The authors found that the TiO2-x films produced by the AP PECVD process performed well in mesoporous perovskite devices with stabilised maximum power point efficiencies up to 13.57% observed for the 1cm2 cells, matching the sputtered reference material. This result may be indicative of a highly uniform and pinhole free film produced by the described AP PECVD process which is supported by the observation that the best performance was achieved by a film in the order of 40 nm thick, which also demonstrates improved fill factor and reduced hysteresis shown on the current density plots. In all cases, the AP PECVD films showed higher mean Voc with narrower distribution than the reference material, again suggesting a lack of pinholes providing high shunt resistance.

It is suggested that increases in perovskite cell efficiency may be obtained by further process optimisation and perhaps a reduction in ETL thickness. Hence, the described approach indicates the potential to enhance perovskite cell performance in addition to demonstrating the viability of an in-line AP PECVD process with clear advantages for cost effective large-scale production.

 

Plasma CVD process shows potential for large area perovskite photovoltaics. Advances in Engineering

 

About the author

Dr. John Hodgkinson is a Research Fellow within the Innovation Research Centre and School of Computing, Science and Engineering at Salford University. His academic career began in 2003 when he left industrial R & D to undertake a PhD supported by a funding award from Pilkington PLC. The work involved the development of a novel atmospheric pressure plasma activated chemical vapour deposition (CVD) system for the production of functional thin films. The success of this work lead to him being responsible for the universities contribution to several European projects (FP7 / H2020) concerned with the design, development and integration of highly novel activated chemical vapour deposition (CVD) and nanoscale surface modification systems for the production of functional thin films for a number of applications (e.g. optical, self-cleaning, infection control, low emissivity, photovoltaic).

During this time, Dr. Hodgkinson also held the position of Senior Scientist at CVD Technologies Ltd. where he conducted and supported commercial research, with a major project being the design, installation and commissioning of an online CVD system for the production of low emissivity glazing.

Profile : Linkedin, Salford University.

About the author

Dr. Heather Yates is a Reader within the Salford Innovation Research Centre and School of Computing, Science and Engineering at Salford University. She received her PhD for work on thin film semiconductors where she was one of the first to achieve room temperature blue luminescence of ZnSe1-y Sy based devices. Since then she has participated widely in a lead role for projects based on atmospheric pressure Chemical Vapour Deposition (CVD) for functional thin films and the development of deposition equipment. These innovative coaters using plasma, flame, thermal and aerosol based CVD are capable of scale-up and integration into industrial in-line processes. Research highlights include the first reported inverse III-V opal systems for photonic applications, along with development of highly efficient silicon and perovskite based solar cells.

Currently she is PI for an EU Horizon 2020 grant CHEOPS related to perovskite solar cell technology via CVD deposition. Present research involves the wide area deposition of functional materials including transparent conducting oxides, antireflection, biocidal and hydrophobic coatings on a range of different substrates. She has produced over 77 peer-reviewed papers and of those, some have been cited in excess of 165 times.

Reference

Hodgkinson, J., Yates, H., Walter, A., Sacchetto, D., Moon, S., & Nicolay, S. (2018). Roll to roll atmospheric pressure plasma enhanced CVD of titania as a step towards the realisation of large area perovskite solar cell technology. Journal of Materials Chemistry C, 6(8), 1988-1995.

Go To Journal of Materials Chemistry C

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