Title Elektronski transport i rekombinacija u amorfnim organskim poluvodičima Title (english) Electronic transport and recombination in amorphous organic semiconductors Author Ivan Jurić Mentor Eduard Tutiš (mentor)Committee member Denis Sunko (predsjednik povjerenstva)Committee member Eduard Tutiš (član povjerenstva)Committee member Miroslav Požek (član povjerenstva)Granter University of Zagreb Defense date and country 2013-10-23, Croatia Scientific / art field, NATURAL SCIENCES Universal decimal classificationUDC ) 53 - Physics Abstract Razumijevanje elektronskih procesa u amorfnim organskim poluvodičima još je, u mnogim pogledima, nepotpuno. Razlog je u složenosti procesa koji se odvijaju stohastičkim pomjeranjem lokaliziranih, koreliranih, električnih naboja u neuređenom mediju. Ovaj rad predstavlja tri doprinosa razumijevanju elektronskih transportnih procesa, ostvarenih upotrebom numeričkih simulacija. Prvi doprinos vezan je za proces elektronsko-šupljinske rekombinacije u anizotropnoj okolini na granici dva različita organska materijala. Pokazujemo da korelirano gibanje elektrona i šupljine na graničnoj površini rezultira redovima veličine većim udarnim presjekom za rekombinacijski proces na granici, u odnosu na istovjetni proces u izotropnoj okolini, te da postoji optimalni raspon parametara unutar kojeg se rekombinacija odvija pretežno u ekscitonskom kanalu. Drugi doprinos povezan je s problemom stacionarnog transporta u energijskom neredu u jako neravnotežnim uvjetima, kada elektronski ansambl pokazuje odlike pseudoravnotežne raspodjele s povišenom, efektivnom temperaturom. Pokazujemo da ta temperatura, za koju nalazimo i analitički izraz u 1D slučaju, dobro opisuje energijsku raspodjelu nosioca, ali ne i transportna svojstva. Lokalna odstupanja od pseudoravnotežne raspodjele, povezana s filamentizacijom strujnog toka, uzrok su nemogućnosti parametrizacije elektronske mobilnosti efektivnom temperaturom. Treći doprinos odgovor je na pitanje kako se svojstva energijskog nereda odražavaju u tranzijentnom električnom odzivu organskih filmova. Pokazujemo da dugovremena atenuacija tamne struje, kakva je opažena u mnogim polimernim filmovima, predstavlja jednoznačan dokaz da raspodjela energijski dubokih elektronskih stanja nije gausijan. Eksponencijalna raspodjela dubokih stanja u suglasju je s eksperimentalno opaženim tranzijetnim odzivom.
Abstract (english) Understanding of the electronic processes in amorphous organic semiconductors is still, in many aspects, incomplete. Reason lies in the complexity of the processes, which are realised through stochastic movement of localised, correlated, electric charges within a disordered medium. This thesis presents three contributions to the understanding of electron transport processes, which have been realised by use of numeric simulations. The first contribution relates to the process of electron-hole recombination in an anisotropic environment at the junction of two different organic materials. We show that the correlated motion of the electron and the hole on the heterojunction surface results in an orders of magnitude larger cross-section for the recombination process on the heterojunction, compared to the same process in an isotropic environment. Further, there is an optimal parameter range within which the recombination is conducted dominantly in the exciton channel. The second contribution is related to the problem of stationary transport in an energetic disorder in conditions far from equilibrium, when the electron ensemble displays features of a quasiequilibrium distribution at an elevated, effective temperature. We show that this temperature, for which we find an analytic expression in 1D case, describes well the energetic distribution of carriers, but not the transport properties. Local deviations from the quasiequilibrium distribution, connected with the filamentisation of the flow, are responsible for the impossibility of parametrisation of the electron mobility by an effective temperature. The third contribution answers the question: how are the features of energetic disorder reflected in the transient electric response of the organic films? We show that the long-timescale attenuation of dark current, seen in many polymer films, represents an unambiguous proof that the density of the energetically deep electronic states is not Gaussian. An exponential distribution of deep states is in accord with experimentally observed transient response.
Keywords
organski poluvodiči
neuređeni sustavi
elektronski transport
elektronska rekombinacija
ekscipleksi
energijski nered
heterogranica
efektivna temperatura
strujni filamenti
DITS
gausijanska gustoća stanja
eksponencijalna gustoća stanja
Keywords (english)
organic semiconductors
disordered systems
electron transport
electron recombination
exciplexes
energetic disorder
heterojunction
effective temperature
current filaments
DITS
Gaussian density of states
exponential density of states
Language croatian URN:NBN urn:nbn:hr:217:208907 Study programme Title: Physics Type of resource Text Extent 253 str. File origin Born digital Access conditions Open access Terms of use Created on 2017-08-23 09:08:11
