Khan, Yousaf (2019) Organic-inorganic nanocomposites for photovoltaic and other optoelectronic applications. (PhD thesis), Kingston University, .
Abstract
Novel nanocomposite organic-inorganic compounds have been synthesised with several layered inorganic hosts (V2O5, MoO3 and ZnPS3). Three synthetic methods were used; direct intercalation taking advantage of any redox chemistry between the host and guest, an ion-exchange route in which pre-intercalated alkali metal cations were exchanged for organic guest cations and recrystallization of the dissolved host around the organic guest species. All methods afforded the intercalation of conducting polymers into the interlayer space of the inorganic hosts. Full characterisation of the composites was carried out as well as the determination of their (opto)electronic properties. The direct method was used to intercalate polyaniline (AnAn+) and 3,4-ethylenedioxythiophene (EDOT) into V2O5 2-amino-5-phenylpyridine (2A5PhPyr) used an acid-base direct intercalation method. AnAn+ and 2A5PhPyr exhibited bilayer structures with AnAn+ parallel to the inorganic layers. EDOT, however, produced a monolayer intercalate and all three products exhibited similar room temperature conductivities (~10-2 – 10-3 Sm-1 ). 2A5PhPyr and 5-aminoquinoline (5AQ) were intercalated into V2O5 and MoO3 using the ion-exchange method. A copolymer of 1,4-phenylenediamine and hydroquinone (1,4PDA-HQ) was also intercalated into V2O5 and 1,2-phenylenediamine (PDA) was intercalated into V2O5, MoO3 and ZnPS3 by this method. 2-Aminothiazole (2AmThia) was intercalated into MoO3 using ion-exchange. PDA and 5AQ exhibited bilayer conformation upon intercalation while PDA was a monolayer intercalant in ZnPS3. PDA intercalated V2O5 and MoO3 exhibited the highest conductivities (~10-1 Sm-1 ) whereas 2AmThia intercalated MoO3 exhibited the lowest conductivity (~10-4 Sm-1 ). Aniline (An) was intercalated into MoO3 via a novel recrystallization method resulting in room temperature conductivity similar to that of the 2AmThia intercalated MoO3 (~10-4 Sm-1 ). The novel ion-exchange of ZnPS3 with Mg2+ yielded MgxZnyPS3 which exhibited substantial interlayer expansion suspected to be due to hydration of intercalated Mg2+. The Mg2+ cations were present in the interlayer spacing and did not occupy the vacant Zn2+ sites. The intercalated materials exhibited p-type properties, unlike their n-type hosts. Using aluminium, copper, tin, zinc and FePS3 as blocking contacts, Schottky devices of the composite materials exhibited improved semiconductor properties over their host materials. Prototype photosensitive devices using V2O5/AnAn+ , V2O5/EDOT, V2O5/2A5PhPyr, MoO3/PDA and ZnPS3/PDA were constructed by spin coating the active material onto ntype silicon and p-type FePS3 and are reported for the first time. The devices exhibited increased photocurrents under ambient light or an incandescent lamp illumination. Maximum efficiencies were 0.71% and 0.26% under ambient light and incandescent lamp respectively. The devices exhibited low charge mobilities of ~8 x 10-10 m 2V -1 s -1 and ~3 x 10-11 m 2V -1 s -1 under ambient sunlight and incandescent light respectively. It was noted that the polymer guests in their most conductive forms produced the best semiconducting and photoactive devices. Overall, this work provided a proof-of-concept that the low-cost organic-inorganic nanocomposite materials synthesised exhibited promising novel optoelectronic properties when incorporated into junction devices.
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