Dr Imalka Jayawardena


Marcus Lee Lecturer
PhD (Surrey), BSc (Hons) in Engineering (Moratuwa, Sri Lanka)
+44 (0)1483 686108
14 ATI 01

Biography

Areas of specialism

Photovoltaics; Perovskites; Organic Semicondutors; Light Emitting Devices; X-Ray detection and Imaging; Nanoelectronics

Research

Research interests

Research collaborations

Triple cation perovskite solar cells

Supervision

Postgraduate research supervision

My teaching

My publications

Publications

Bowei Li, Yuren Xiang, Imalka Jayawardena, Deying Luo, John Watts, Steven Hinder, Hui Li, Victoria Ferguson, Haitian Luo, Rui Zhu, Ravi Silva, Wei Zhang (2020)Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells, In: Solar RRL4(5)2000060 Wiley

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

Mozhgan Yavari, Xueping Liu, Thomas Webb, K D G Imalka Jayawardena, Yuren Xiang, Stefanie Kern, Steven Hinder, Thomas J Macdonald, S Ravi P Silva, Stephen J Sweeney, Wei Zhang (2021)A synergistic Cs2CO3 ETL treatment to incorporate Cs cation into perovskite solar cells via two-step scalable fabrication, In: Journal of Materials Chemistry C Materials for optical and electronic devices9(12)pp. 4367-4377 Royal Society of Chemistry

Triple cation CsFAMA perovskite films fabricated via a one-step method have recently gained attention as an outstanding light-harvesting layer for photovoltaic devices. However, questions remain over the suitability of one-step processes for the production of large-area films, owing to difficulties in controlling the crystallinity, in particular, scaling of the frequently used anti-solvent washing step. This can be mitigated through the use of the two-step method which has recently been used to produce large-area films via techniques such as slot dye coating, spray coating or printing techniques. Nevertheless, the poor solubility of Cs containing salts in IPA solutions has posed a challenge for forming triple cation perovskite films using the two-step method. In this study, we tackle this challenge through fabricating perovskite films on a caesium carbonate (Cs2CO3) precursor layer, enabling Cs incorporation within the film. Synergistically, we find that Cs2CO3 passivates the SnO2 electron transport layer (ETL) through interactions with Sn 3d orbitals, thereby promoting a reduction in trap states. Devices prepared with Cs2CO3 treatment also exhibited an improvement in the power conversion efficiency (PCE) from 19.73% in a control device to 20.96% (AM 1.5G, 100 mW cm−2) in the champion device. The Cs2CO3 treated devices (CsFAMA) showed improved stability, with un-encapsulated devices retaining nearly 80% efficiency after 20 days in ambient air.

MAE Abdel-Rahman, A Lohstroh, I Jayawardena, SJ Henley (2012)The X-ray detection performance of polycrystalline CVD diamond with pulsed laser deposited carbon electrodes, In: Diamond and Related Materials22pp. 70-76 Elsevier

The deposition of amorphous carbon electrical contacts on a diamond radiation detector by Pulsed Laser Deposition (PLD) is introduced as a novel technique for producing tissue equivalent X-ray dosimeters. Three devices were fabricated with the following electrical contacts: pure amorphous carbon (labelled Poly-C), amorphous carbon mixed with Nickel (PLD) (labelled Poly-C/Ni) and conventional sputtered Pt (labelled Poly-Pt). To examine the performance of PLD carbon as a contact, a set of X-ray detection characteristics was studied and compared to those of Poly-Pt. This investigation includes current–voltage characteristics, linearity and dose rate dependence, sensitivity and specific sensitivity, photoconductive gain, stability, reproducibility and time response (rise and fall-off times). The experimental results suggest that Poly-C/Ni is suitable for an X-ray dosimeter. It shows a high signal to noise ratio (SNR) of ~ 3300, approximately linear relationship between the photocurrent and the dose rate and a sensitivity of 65 nC/Gy. In addition the current signal is stable and reproducible (within 0.26%) and the rise and fall-off times are less than 1.1 and 0.4 s, respectively.

R. D. I. G Dharmasena, K. D. G. I Jayawardena, Zakaria Saadi, Xuhui Yao, R. M. I Bandara, Yunlong Zhao, S. R. P Silva (2019)Energy Scavenging and Powering E-Skin Functional Devices, In: Proceedings of the IEEE107(10)pp. 2118-2136 IEEE

Electronic skins (e-skins), which can seamlessly adapt and adhere to the body to mimic the functionality of human skin, are a rapidly emerging research area. Such e-skins have the potential to revolutionize artificial prosthetics, robotics, human-machine interfacing, and health monitoring applications. Powering the e-skin is a critical challenge at present due to strict performance criteria, including flexibility, stretchability, mobility, and autonomous operation. One of the most promising approaches to overcome some of these challenges is to scavenge energy from the human body's movements and its surrounding environment. This paper outlines some of the key potential developments that enable energy harvesting through mechanical, thermal affects, and low light sources, as well as energy management and storage technologies, which could lead toward the construction of autonomous e-skin modules and self-powered sensing systems.

LYNN TUMILTY, M. Prabodhi A. Nanayakkara , Lidija Matjačić , Sebastian Wood, Filipe Richheimer , Fernando A. Castro, Sandra Jenatsch, Simon Züfle, Rachel Kilbride, Andrew J. Parnell, Mateus G. Masteghin, Hashini M. Thirimanne, Andrew Nisbet, K. D. G. Imalka Jayawardena, S. Ravi P. Silva (2020)Ultra-Low Dark Current Organic-Inorganic Hybrid X-Ray Detectors, In: Advanced functional materials2008482 Wiley
Randunu Devage Ishara Gihan Dharmasena, Imalka Jayawardena, Christopher Mills, Jonathan Deane, Jose Anguita, Robert Dorey, S Silva (2017)Triboelectric Nanogenerators: Providing a Fundamental Framework, In: Energy & Environmental Science10(8)pp. 1801-1811 Royal Society of Chemistry

A new model which comprehensively explains the working principles of contact-mode Triboelectric Nanogenerators (TENGs) based on Maxwell’s equations is presented. Unlike previous models which are restricted to known simple geometries and derived using the parallel plate capacitor model, this model is generic and can be modified to a wide range of geometries and surface topographies. We introduce the concept of a distance-dependent electric field, a factor not taken in to account in previous models, to calculate the current, voltage, charge, and power output under different experimental conditions. The versatality of the model is demonstrated for non-planar geometry consisting of a covex-conave surface. The theoretical results show excellent agreement with experimental TENGs. Our model provides a complete understanding of the working principles of TENGs, and accurately predicts the output trends, which enables the design of more efficient TENG structures.

Harry M Cronin, K D G Imalka Jayawardena, Zlatka Stoeva, Maxim Shkunov, S Ravi P Silva (2017)Effects of ambient humidity on the optimum annealing time of mixed-halide Perovskite solar cells, In: Nanotechnology28(11) IOP Publishing

Mixed halide Perovskite solar cells (PSCs) are commonly produced by depositing PbCl2 and CH3NH3I from a common solvent followed by thermal annealing, which in an up-scaled manufacturing process is likely to take place under ambient conditions. However, it has been reported that, similar to the effects of thermal annealing, ambient humidity also affects the crystallisation behaviour and subsequent growth of the Perovskite films. This implies that both of these factors must be accounted for in solar cell production. In this work, we report for the first time the correlation between the annealing time, relative humidity (RH) and device performance for inverted, mixed halide CH3NH3PbI(3−x)Cl x PSCs with active area ≈1 cm2. We find a trade-off between ambient humidity and the required annealing time to produce efficient solar cells, with low humidities needing longer annealing times and vice-versa. At around 20% RH, device performance weakly depends on annealing time, but at higher (30%–40% RH) or lower (0%–15% RH) humidities it is very sensitive. Processing in humid environments is shown to lead to the growth of both larger Perovskite grains and larger voids; similar to the effect of thermal annealing, which also leads to grain growth. Therefore, samples which are annealed for too long under high humidity show loss of performance due to low open circuit voltage caused by an increased number of shunt paths. Based on these results it is clear that humidity and annealing time are closely interrelated and both are important factors affecting the performance of PSCs. The findings of this work open a route for reduced annealing times to be employed by control of humidity; critical in roll-to-roll manufacture where low manufacturing time is preferred for cost reductions.

K. D. G. Imalka Jayawardena, Hashini M. Thirimanne, Sandro Francesco Tedde, Judith E. Huerdler, Andrew J. Parnell, R. M. Indrachapa Bandara, Christopher A. Mills, S. Ravi P. Silva (2019)Millimeter-Scale Unipolar Transport in High Sensitivity Organic–Inorganic Semiconductor X-ray Detectors, In: ACS Nano American Chemical Society

Hybrid inorganic-in-organic semiconductors are an attractive class of materials for optoelectronic applications. Traditionally, the thicknesses of organic semiconductors are kept below 1 μm due to poor charge transport in such systems. However, recent work suggests that charge carriers in such organic semiconductors can be transported over centimeter length scales opposing this view. In this work, a unipolar X-ray photoconductor based on a bulk heterojunction architecture, consisting of poly(3-hexylthiophene), a C70 derivative, and high atomic number bismuth oxide nanoparticles operating in the 0.1–1 mm thickness regime is demonstrated, having a high sensitivity of ∼160 μC mGy–1 cm–3. The high performance enabled by hole drift lengths approaching a millimeter facilitates a device architecture allowing a high fraction of the incident X-rays to be attenuated. An X-ray imager is demonstrated with sufficient resolution for security applications such as portable baggage screening at border crossings and public events and scalable medical applications.

MAHESHANI PRABODHI ALWIS NANAYAKKARA, MATEUS GALLUCCI MASTEGHIN, Laura Basiricò, Ilaria Fratelli, Andrea Ciavatti, Rachel Kilbride, Sandra Jenatsch, THOMAS WEBB, FILIPE MASUCH RICHHEIMER, Sebastian Wood, Fernando A. Castro, Andrew J. Parnell, Beatrice Fraboni, IMALKA JAYAWARDENA, S RAVI PRADIP SILVA (2021)Molecular weight tuning of organic semiconductors for curved organic-inorganic hybrid X-ray detectors, In: Advanced Science Wiley

Curved X-ray detectors have the potential to revolutionise diverse sectors due to benefits such as reduced image distortion and vignetting compared to their planar counterparts. While the use of inorganic semiconductors for curved detectors are restricted by their brittle nature, organic-inorganic hybrid semiconductors which incorporated bismuth oxide nanoparticles in an organic bulk heterojunction consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) are considered to be more promising in this regard. However, the influence of the P3HT molecular weight on the mechanical stability of curved, thick X-ray detectors remains less well understood. Herein, high P3HT molecular weights (>40 kDa) are identified to allow increased intermolecular bonding and chain entanglements, resulting in X-ray detectors that can be curved to a radius as low as 1.3 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard dark current of