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Title: Investigation of solar cells and phototransistors based on hybrid copper (I) thiocyanate : methanofullerene materials
Author: Sit, Wai Yu
ISNI:       0000 0004 9350 8267
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2020
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The combination of organic and inorganic semiconductors offers a route to the development of solar cells and other optoelectronic devices that combine flexibility, high efficiency and high stability. In this thesis, we have investigated the hybrid organic: inorganic system, copper (I) thiocyanate (CuSCN): phenyl C71 butyric methyl acid ester (PC70BM). We have shown that ~100 nm long CuSCN nanowires can be grown within PC70BM when a layer of PC70BM containing dilute CuSCN is deposited on top of a CuSCN layer on a heated substrate. Photovoltaic devices made from these nanowire-containing layers perform significantly better than devices made from CuSCN/PC70BM bilayers because the nanowires improve charge collection efficiency. The initial device based on a nanowire-containing CuSCN:PC70BM structure, the device shows ~5% power conversion efficiency. We show that these CuSCN NWs form well when the substrate temperature is about 115oC. We then discovered that by spin-coating interlayers with a CuSCN rich precursor solution between the compact CuSCN layer and CuSCN:PC70BM photoactive mixed layer, the power conversion efficiency could be further improved to nearly 6% power conversion efficiency. Finally, we measured the carrier mobility of CuSCN:PC70BM layer using field-effect transistors. We find the carrier mobility values for holes and electrons to be on the order of 10-3 to 10-2 cm2/Vs, similar to values for typical organic semiconducting materials. We have also characterized the same device as a phototransistor by illuminating the active area with light in the visible range. This work has demonstrated the concept of the initial application of CuSCN nanowires, which has never been reported in any organic: inorganic mixed layer. CuSCN nanowires could be a new approach for optimizing charge separation in light-absorbing acceptor systems.
Supervisor: Anthopoulos, Thomas ; Nelson, Jenny Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral