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Title: Alternative perovskites for photovoltaics
Author: McDonald, Calum James
ISNI:       0000 0004 6424 7846
Awarding Body: Ulster University
Current Institution: Ulster University
Date of Award: 2017
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This thesis explores new types of perovskite and perovskite-like materials for photovoltaics, with a view towards demonstrating novel and low-cost materials such as metal oxide perovskites for photovoltaics. The first part explores the prototypical organometal halide perovskite CH3NH3Pbl3, where CH3NH3 = methylammonium (MA). MAPbl3 has been studied by the partial replacement of its organic component, MA, with the larger molecule ethylenediammonium (EDA), with the chemical formula NH3(CH2)2NH3. This in turn introduces vacancies into EDA-containing MAPbl3, which has allowed the study of a non-stoichiometric organometal halide perovskite. This work observed that the partial replacement of the MA molecule with a larger molecule reduced the hysteresis. Following this, the low-cost perovskite-like material methylammonium iodo bismuthate has been studied. Methylammonium iodo bismuthate has the chemical formula MA3Bi2lg (MABI), and forms a zero­dimensional network of Bi2lg bioctahedra with quantum confinement. MABI has been characterised and used to fabricate solar cells. This bulk material with an ordered zero-dimensional internal structure exhibits carrier multiplication, and this thesis has demonstrated the fabrication of MABI solar cells. The structure has also been shown to favourably accommodate a small quantity of quantum confined silicon nanocrystals, opening up an avenue of possible hybrid devices which can be explored. Building on this knowledge, this thesis then explores two perovskite oxide materials which have not previously been demonstrated in photovoltaics. Both perovskite oxides exhibit strong and broad visible light absorption which extends into the near-infrared spectrum. One of which, Sr-deficient strontium niobate (Sro.gNb03), exhibits metallic conduction, and has been demonstrated in a photovoltaic cell for the first time. This work demonstrates the possibility of extracting excited carriers in a metal oxide with metallic conduction. The metal oxide perovskite calcium manganite, Ca2Mn2O5, has also been explored for photovoltaics. Ca2Mn2O5 is a plasmonic metal oxide and is therefore highly attractive material for photovoltaics. Solar cells were successfully fabricated using Ca2Mn2O5, and these results demonstrate the possibility of carrier extraction and highlight great opportunities for solar energy harvesting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available