Magneto-electrical Study of Novel Materials and Devices for Energy Harvesting


Student thesis: Doctoral Thesis

View graph of relations


Awarding Institution
Award date24 Aug 2021


This thesis consists of two main studies: tuning spin-exchange energy and magneto-photocurrent in organo-metal halide perovskites and a study on the application of 2D materials to extend the absorption spectrum of silicon to longer wavelengths.

In the first study, magneto-electric characterization of organo-metal halide perovskites cells was performed to study spin-dependent, intrinsic properties of perovskite materials. The optical and electronic properties of perovskite materials are spin dependent. Therefore, tuning the spin-exchange energy between the photogenerated excited states in perovskite materials can provide a way towards improving their photovoltaic and light emission properties. Spin-exchange energy between carriers is due to the Coulomb interaction between an electron and a hole in excited states which depends on the separation distance between these carriers. Therefore, tuning e-h pairs separation distance can result to tuning the strength of spin-exchange energy between electron and hole. Through magneto-photocurrent experiment, the effect of photo-excitation intensities on spin-exchange energy in hybrid perovskite-based devices was investigated. It was demonstrated that high photon intensity generates large density of carriers which leads to long-range Coulomb interaction between the carriers. The long-range interaction increases the distance between electron and hole and so, reduces spin exchange energy and increases the changing rate of singlet/triplet ratio. Besides, at light wavelengths comparable with the band gap of perovskite material, magneto-photocurrent polarity was observed to change between negative and positive values. Doping with manganese was also demonstrated as an additional way of tuning long-range spin exchange energy between the photo-generated excited states. These findings suggest a novel approach to tune spin-exchange energy and magneto-photocurrent in organo-metal halide perovskites and thus, provide further insight into understanding the mechanisms that can affect photovoltaic device performance.

The second study is on the application of two-dimensional (2D) semiconducting materials to enhance solar absorption spectrum of silicon. Platinum diselenide (PtSe2) and multilayer graphene (MLG) were the 2 D semiconducting materials exploited in this work. Silicon (Si) is a prototypical inorganic material for photovoltaic conversion. Therefore, any approach that can engineer its optoelectronic properties would provide insight into further improving its photovoltaic performance. In this thesis, it was shown that the spectrum of silicon can be extended to longer wavelengths via 2D/Si heterojunction. Photo-induced Hall effect, in conjunction with standard absorption spectroscopy were employed to estimate the increase in photo-conversion efficiency of 2D/ Silicon heterojunction.

The first chapter of this thesis gives an overview of photovoltaic cells, different kinds of photovoltaic cells, introduction to 2D semiconducting materials and magnetic field effects in hybrid perovskite materials. Photo-induced Hall effect in semiconductor and the challenges and motivation of this work were also discussed.

In the second chapter, details of the experimental procedure were reported. These include the methods of sample preparations and the characterization techniques. The results of this work were presented in chapter 3, 4 and 5. In particular, in chapter 3, findings on spin-dependent carrier recombination and exciton dissociation in hybrid photovoltaic materials using magneto-photocurrent experiment, were reported. In chapter 4 and 5, the application of 2D semiconductors (PtSe2 and multilayer graphene) for extending the near infrared band-edge absorption spectrum of silicon was reported.

Lastly, conclusions drawn from this work and future perspectives were provided.