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dc.contributor.authorRichter, Johannes Martin
dc.date.accessioned2018-05-04T11:48:41Z
dc.date.available2018-05-04T11:48:41Z
dc.date.issued2018-05-19
dc.date.submitted2017-12-01
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/275568
dc.description.abstractLead halide perovskites have shown remarkable device performance in both solar cells and LEDs. Whilst the research efforts so far have been mainly focussed on device optimisation, little is known about the photophysical properties. For example, the nature of the bandgap is still debated and an indirect bandgap due to a Rashba splitting has been suggested. In this thesis, we study the early-time carrier relaxation and its impact on photoluminescence emission. We first study ultrafast carrier thermalization processes using 2D electronic spectroscopy and extract characteristic carrier thermalization times from below 10 fs to 85 fs. We then investigate the early-time photoluminescence emission during carrier cooling. We observe that the luminescence signal shows a rise over 2 picoseconds in CH3NH3PbI3 while carriers cool to the band edge. This shows that luminescence of hot carriers is slower than that of cold carriers, as is found in direct gap semiconductors. We conclude that electrons and holes show strong overlap in momentum space, despite the potential presence of a small band offset arising from a Rashba effect. Recombination and device performance of perovskites are thus better described within a direct bandgap model. We finally study carrier recombination in perovskites and the impact of photon recycling. We show that, for an internal photoluminescence quantum yield of 70%, we measure external yields as low as 15% in planar films, where light out-coupling is inefficient, but observe values as high as 57% in films on textured substrates that enhance out-coupling. We study the photo-excited carrier dynamics and use a rate equation to relate radiative and non-radiative recombination events to measured photoluminescence efficiencies. We conclude that the use of textured active layers has the ability to improve power conversion efficiencies for both LEDs and solar cells.
dc.description.sponsorshipWinton Programme for Physics of Sustainability, EPSRC studentship, Cambridge Trust Scholarship
dc.language.isoen
dc.rightsAll rights reserved
dc.subjectsemiconductor
dc.subjectphysics
dc.subjectperovskites
dc.subjectlead halide perovskites
dc.subjectultrafast spectroscopy
dc.subjectfemtosecond photoluminescence
dc.subjectsemiconductor physics
dc.subjectcharge carrier recombination
dc.subjectcharge carrier relaxation
dc.subjectoptoelectronics
dc.subjectPLQE
dc.subjectlight out-coupling
dc.titleCharge Carrier Relaxation in Halide Perovskite Semiconductors for Optoelectronic Applications
dc.typeThesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.publisher.departmentPhysics
dc.date.updated2018-05-03T17:32:17Z
dc.identifier.doi10.17863/CAM.22811
dc.publisher.collegeGonville & Caius
dc.type.qualificationtitlePhD in Physics
cam.supervisorFriend, Richard Henry
cam.thesis.fundingtrue
rioxxterms.freetoread.startdate2400-01-01


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