Unconventional materials for light-emitting and photovoltaic applications
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2018
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01-06-2018
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Ortí Guillén, Enrique
Bolink, Henk
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Abstract
The motivation of this thesis is to reduce the energy consumption to generate illumination and the amount of fuel fossil employed in the generation of energy. For this purpose, novel, efficient and low-cost electroluminescent and photovoltaic devices need to be developed.
The work was focused on the development of red- and near-infrared LECs and the improvement of the device stability. The iTMCs studied were based on the [Ir(ppy)2(btzpy)][PF6] complex (ppy = 2-phenylpyridinate and btzpy = 2-(pyridin-2-yl)benzo[d]thiazole) and all of the complexes showed red- and near-infrared photoluminescence in the solid-state with moderate PLQYs values (<18%). The LECs prepared with the complexes also exhibit red to near-infrared electroluminescence. Although the maximum luminance values were moderate, they exhibited extremely high device stability with lifetimes in the range of 1000–6000 h, being the most stable red-emitting LECs reported up to date. The EQEs obtained were moderate (EQE<2%), however, these values were impressive in view of its low PLQY values and the high current density applied. Moreover, the possibility of tuning the luminance levels was demonstrated, having a fast response with almost no loss in device stability, maintaining its impressive characteristics by increasing the average current density.
An in-depth study of the photovoltaic efficiency by increasing the photocurrent obtained through modification of the perovskite thickness was performed. A series of vacuum-deposited MAPbI3 layers with layer thicknesses ranging from 210 to 900 nm were fabricated and implemented into p-i-n devices. The JSC was enhanced when the perovskite thickness was increased but the FF and hence the PCE was reduced due to the low mobility of the polyTPD layer. The partial oxidation of the polyTPD layer increases its conductivity and the device recovers the FF reaching a PCE of 12.7%, being the same high efficiency than the most efficient device of the series with thinner perovskite films (12%). In this work was demonstrated that with non-limiting organic layers, the PV performance of vacuum-deposited perovskite solar cells is independent on the perovskite layer thickness and that the charge carrier diffusion length is not limiting in the devices.
Fully vacuum-deposited p-i-n and n-i-p perovskite solar cells, employing a MAPbI3 perovskite layer deposited between an intrinsic and doped n- or p- type organic charge transport layers, respectively, were fabricated. The optimization of the dopant concentration was carried out and it was found that the presence of the undoped and doped charge transport layers were required for highly efficient solar cells. The optimized solar cells lead to hysteresis-free and very high efficiencies exceeding 16.5% (p-i-n) and 20% (n-i-p), the highest efficiencies reported for vacuum-deposited perovskite and for MAPbI3-based solar cells.