Optimisation of CdTe(1-X)SeX and MgXZn(1-X)O layers for CdTe PV devices



Baines, Tom
(2020) Optimisation of CdTe(1-X)SeX and MgXZn(1-X)O layers for CdTe PV devices. PhD thesis, University of Liverpool.

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Abstract

This thesis presents a study on the optimisation of CdTe(1-X)SeX and MZO layers for CdTe PV applications. The first part of this work focused on the formation of the CdTe(1-X)SeX layers using CdSe layer and its impact on solar cell performance. Initially the incorporation of CdSe layer into conventional CdS/CdTe devices was investigated. This approach was found to be detrimental to all device parameters particularly JSC due to the formation of a CdS(1-X)SeX phase at the CdTe/CdSe/CdS interface. This phase increased the amount of parasitic absorption observed at short wavelength, reduced PV performance, and resulted in excessive void formation at the CdTe device interface. Replacement of CdS with SnO2 as the junction partner layer was found to increase the device photo response at both short and long wavelength due to removal of the CdS and efficient formation of the CdTe(1-X)SeX phase. This resulted in increased device performance of > 13% with notably high JSC values of > 29 mA cm-2. However, removal of CdS did result in a reduced VOC and interface voids were still present. Focus was then placed on alternative oxides to SnO2 which could act as the device window layer but simple binary oxides tested, ZnO, TiO2 and FTO were all found to reduce performance compared to SnO2. The second part of this work therefore investigated MZO layers for CdTe PV. Two approaches were studied, co-sputtering from ZnO and MgO targets or sputtering from a single MZO target. The use of co-sputtered MZO layers was found to be detrimental to performance, due to the high resistivity of the layers and the formation of S-shaped JV curves related to interface charge accumulation. Initially use of single target MZO layers similarly resulted in S-shaped curves and poor performance however, post-growth annealing of the MZO converted the material from amorphous to crystalline and enhanced conductivity of the MZO, removing the charge accumulation. Despite the reduced overall performance compared to SnO2, 11.3% and 13.5% respectively, the MZO devices had an improved VOC demonstrating that with further optimisation of the device junction interface further improvements to performance could be achieved.

Item Type: Thesis (PhD)
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 09 Apr 2020 13:47
Last Modified: 09 Nov 2021 08:12
DOI: 10.17638/03078662
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3078662