2020 - 2022
Dr. Revathy Padmanabhan
SERB - Start-up Research Grant (SRG)
Perovskites are the basis of many multi-functional optically-sensitive devices such as solar cells and photodetectors. They can be processed using solution-based techniques and are suitable for applications on flexible substrates. While the rapid improvement in performance of these devices have been reported extensively, the reasons accounting for different losses (hence, performance limits) have not been studied as thoroughly. Most reports that provide maximum theoretical efficiency do not account for electron and hole transport layers (ETL and HTL). Nair et al., [J Appl Phys, 2018] provides a more integrated approach in terms of calculation of theoretical efficiency by accounting for ETL and HTL; however, their analysis is confined to a simple structure. In this context, we propose to explore different device designs/architectures. Our calculations show that most ETLs behave as anti-reflection coatings (ARCs). Therefore, one of our proposed architectures is a simple stack of multiple ETLs (so that they exhibit better ARC behaviour); the order of each ETL in the stack is such that their band-offsets do not hinder electron transport. Another proposed architecture is to have different ETL materials in a grid structure; fabricating this will need multiple lithography steps. We can also modify this design to make grids with different geometries/dimensions. We anticipate that fringing effects and other non-classical plasmonic effects will become dominant, specially when grid dimensions are very small; this can contribute to enhanced optical response. We also propose to design devices with isolated optical and electrical input ports; any non-ETL material can be chosen as the ARC stack here. One of our objectives is to extract spectral responsivity of these devices (which is crucial for detector applications). Also, we propose to design detectors that yields high responsivities only in UV regime, by designing plasmonic structures. Analysis of each device design entails exploring different materials, dimensions, geometries, and analysing different loss mechanisms at every layer and interface; this will also involve computations to optimise thickness of each layer. Lumerical FDTD will be used to simulate and evaluate the performance of different devices, initially. Once the proposed device designs are optimised by computation and simulation, we will fabricate and characterise these devices. We will also build a calibrated optical setup that will include optical sources covering a range of wavelengths, whose output will then be fed to the fabricated devices. Successful completion of this project willprovide an integrated approach (accounting for optical and electronic properties of all layers) to calculate a more accurate efficiency limit for any given device structure; this will be our key contribution. This will lead to fabrication and characterisation of devices whose structures and dimensions have been optimised to yield maximum efficiencies.