Spray deposition for plastic electronics
File(s)
Author(s)
Roy, Kirsty
Type
Thesis
Abstract
Spray deposition is a promising technique for the solution processing of plastic electronic devices due to its potential for high-speed, large-scale device fabrication using low capital cost equipment. Most recent reports of spray-deposited electronic devices have used ultrasonic systems for film deposition to minimise surface roughness, but such systems suffer from low materials throughput, and are consequently ill-suited to industrial manufacturing. Gas-driven spray-heads enable higher throughput materials delivery but can result in an unacceptably rough film due to the large, broadly distributed droplet sizes that are often generated and the hard-impact nature of the deposition process.
This thesis describes a new automated gas-driven spray coater for the controlled deposition of a broad variety of solution processed electronic materials. It is specifically suited to the deposition of polymer films such as poly(3-hexylthiophene) (P3HT), overcoming many of the usual disadvantages of conventional gas-driven spray coaters. Key features of the system include: a novel, high performance 3D-printed spray-head for the generation of ultrafine sprays; full three-dimensional position and velocity control of the spray head; integrated temperature control; and independent control of solution and gas flow rates.
To determine the optimum solution composition for spray-deposition of P3HT films, the aggregation and gelation dynamics of various P3HT/o-xylene solutions were first investigated by static light scattering. On the basis of these measurements, we conclude that dilute solutions (with polymer concentration <5 mg/ml) of low (<20 kg/mol ) molecular weight polymer containing a small amount of a secondary solvent. are optimal for avoiding gelation and clogging of the spay-head. For higher weight material, heating of the solution is necessary to avoid gelation.
The thesis also describes the development of an optical profiling technique for the characterisation of polymer films, which provides a fast method for quantitatively characterising the uniformity of large-area, thin polymer films. Using this technique, we were able to confirm that the spray-deposition system yields high quality, thin semiconducting polymer films, allowing for the controlled fabrication of active layers in organic photovoltaic devices from non-chlorinated solvents. The influence of solution composition and deposition variables such as gas pressure, solvent composition and substrate temperature were investigated, and optimised conditions for the deposition of high quality (device-grade) thin P3HT films were thereby identified.
A maximum device efficiency of 4.0 % was achieved for the spray-deposited bulk heterojunction P3HT:fullerene films processed from xylene. The results indicate that, providing the active layer is continuous, high device efficiency may be achieved even with relatively rough films, spray-coated from non-chlorinated processing solvents.
This thesis describes a new automated gas-driven spray coater for the controlled deposition of a broad variety of solution processed electronic materials. It is specifically suited to the deposition of polymer films such as poly(3-hexylthiophene) (P3HT), overcoming many of the usual disadvantages of conventional gas-driven spray coaters. Key features of the system include: a novel, high performance 3D-printed spray-head for the generation of ultrafine sprays; full three-dimensional position and velocity control of the spray head; integrated temperature control; and independent control of solution and gas flow rates.
To determine the optimum solution composition for spray-deposition of P3HT films, the aggregation and gelation dynamics of various P3HT/o-xylene solutions were first investigated by static light scattering. On the basis of these measurements, we conclude that dilute solutions (with polymer concentration <5 mg/ml) of low (<20 kg/mol ) molecular weight polymer containing a small amount of a secondary solvent. are optimal for avoiding gelation and clogging of the spay-head. For higher weight material, heating of the solution is necessary to avoid gelation.
The thesis also describes the development of an optical profiling technique for the characterisation of polymer films, which provides a fast method for quantitatively characterising the uniformity of large-area, thin polymer films. Using this technique, we were able to confirm that the spray-deposition system yields high quality, thin semiconducting polymer films, allowing for the controlled fabrication of active layers in organic photovoltaic devices from non-chlorinated solvents. The influence of solution composition and deposition variables such as gas pressure, solvent composition and substrate temperature were investigated, and optimised conditions for the deposition of high quality (device-grade) thin P3HT films were thereby identified.
A maximum device efficiency of 4.0 % was achieved for the spray-deposited bulk heterojunction P3HT:fullerene films processed from xylene. The results indicate that, providing the active layer is continuous, high device efficiency may be achieved even with relatively rough films, spray-coated from non-chlorinated processing solvents.
Version
Open Access
Date Issued
2016-03
Date Awarded
2017-03
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
McLachlan, Martyn
Heeney, Martin
Stavrinou, Paul
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)