Modelling And Simulation Of Quantum Dot Intermediate Band Solar Cell

This thesis presents theoretical work on the intermediate band solar cell(IBSC)which is divided into two main parts.The first part is the study of electronic and optical properties of individual quantum dots.These properties are further studied for the quantum dots(QDs)in super lattice structures.The second part consists of the modelling of the solar cell device.The parametric optimization is investigated leading towards the simulation of intermediate band solar cell.The efficiency of intermediate band solar cell is investigated as function of layer thickness and band flatness.The flatness is controlled by the doping concentrations of the layers surrounding intermediate band layer.The electronic states and optical properties of self assembled InAs quantum dots embedded in GaAs matrix have been investigated.Their carrier confinement energies for single quantum dot are calculated by time-independent Schr?dinger Equation(SE)in which hamiltonianian of the system is based on effective mass approximation and position-dependent electron momentum.Transition energy,absorption coefficient,refractive index and high frequency dielectric constant for spherical,cylindrical and conical quantum dots with different sizes in different dimensions are calculated.Comparative studies have revealed that size and shape greatly affect the electronic transition energies and absorption coefficient.Peaks of absorption coefficients have been found to be highly shape-dependent.We have applied tight binding model for the investigation of ground state energies using time-independent SE with effective mass approximation.It has been investigated that the electron energies are confined due to wave function delocalization in closely coupled QD structures.The minimum ground state energy can be obtained by increasing the periodicity and decreasing the barrier layer thickness.We have calculated electronic and optical properties which include ground state energy,transition energy,density of state,absorption coefficient and refractive index,which can be tuned by structure modification.In our results,the minimum ground state energy is achieved to be 0.25e V with a maximum period of 10 QDs.The minimum transition energies from band to band and band to continuum energy level are 63me V and 130me V with 2nm barrier layer thickness respectively.The absorption coefficient of our proposed QD superlattice(SL)model is found to be maximum1.2x10⁴cm^-1and can be suitable for highly sensitive infrared detector and high efficiency solar cells.A solar cell model is presented,in which dependence of quantum efficiency on various parameters,has been investigated.The mobility of the carrier has varied with wide range along with the carrier lifetime.The effect of surface recombination velocity has also been brought under observation.Results show that the higher photovoltaic efficiency can be achieved by increasing the mobility and carrier lifetime while decreasing the surface recombination velocity.Theoretical model of InAs/GaAs IBSC has been proposed,where we have calculated the effect of variation in the thickness of intrinsic and IB layer on the efficiency of the solar cell using detailed balance theory.IB energies have been optimized for different IB layer thickness.Maximum efficiency 46.6%is calculated for IB material under maximum optical intensity including only radiative recombination.We have proposed method to control the band flatness of the intermediate band in quantum dot solar cells.The flatness is achieved by optimizing the doping concentration and fermi level of the surrounding layers.Results show that the maximum efficiency 44.12%can be achieved including radiative and non-radiative recombination under maximum optical intensity.