Optoelectronic characterization of organic photovoltaic devices with emerging achitectures

• Ano de defesa: 2020
• Autor(a) principal: Lima Filho, Joaquim Brasil de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Capacitor coletor de luz; Continuous-wave photoinduced absorption spectroscopy; Eletrônica orgânica; Espectroscopia de absorção fotoinduzida por onda contínua; Espectroscopia de impedância; Impedance spectroscopy; Light harvesting capacitor; Organic electronics; Redes metálicas montadas em superfície; Surface metal-organic frame-works
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/76/76132/tde-28092020-142014/

Following the worldwide interest in organic electronics ( OE ) devices, the first part of this work aimed at setting up an experimental apparatus for continuous-wave photoinduced absorption ( cw-PA ) spectroscopy with potential application to the characterization of organic photovoltaic ( OPV ) devices. This technique is part of a group known as pump- probe spectroscopy, which requires two light sources: one for pumping and the other one for probing the sample under investigation. The cw-PA spectroscopy allows the characterization of long-lasting photogenerated species in OPV s. The optical spectra of such species yield relative changes in transmission of the probe beam that are typically in the order of 10-4 . To obtain these spectra, the setup was assembled with advanced detection techniques based on a lock-in amplifier ( LIA ), with pumplight modulation at frequencies ranging from Hz to MHz. This feature makes cw-PA an important tool for the investigation of both dynamics and kinetics of photogenerated species. The setup was automated using LabView® and subjected to several tests to establish its reliability. After passed all the tests, the setup was applied to characterize devices with emerging architectures. One of them was the surface metal-organic frameworks ( SURMOFs ), which can form organized crystalline structure achieved with application of organic materials. After having preliminary photoconductivity results with SURMOFs based on buckminsterfullerene ( C60 ) and 5,15-bis-(3,4,5-trimethoxyphenyl)-10,20-bis(4-carboxyphe- nyl) porphyrinato zinc-II ( ZnTPP ) fabricated at Institute of Functional Interfaces ( IFG ), Karlsruhe Institute of Technology ( KIT ), in Germany, professor Wöll sent some samples to our laboratory to be further characterized. Measurements with cw-PA and current- voltage ( JV ) showed that the devices present poor charge photogeneration, with low short circuit current, open circuit voltage, and fill factor. The poor photogeneration may be caused by the low ratio acceptor/donor, while the low short circuit current, open circuit voltage, and fill factor may be caused by the assembling of C60 in a cage on ZnTPP , in which case C60 molecules are not electronically connected with each other and may be working as a sink (or trap) of electrons. Another emerging architecture named the light harvesting capacitor ( LHC ) differs from the usual OPV s because it drives an output current without charge collection. The photogenerated charges are stored in nanodipoles within the dielectric layer when the device is illuminated and the LHC outputs peaked current upon illumination by modulated light, differently from the usual photovoltaic devices. The second part of this work aimed at developing a mathematical model for LHC s as well as fabricating and characterizing an LHC . For the fabrication, the polymer poly(3- potassium-6-hexanoate thiophene) ( P3KHT ) was used as electron donor and two organic molecules, namely the N,N´-bis(6-aminohexil)-3,4,9,10-perilenediimide ( P6N ) and the perylenediimide-polyethileneimine ( PDI-PEI ) as electron acceptors. The layer-by-layer ( LbL ) assemblies led to very thin films with average thickness of ~ 1.5 nm . Results obtained from multi layer LHC s built with up to 30 active bilayers sandwiched by insulating bilayers are presented. Results from ultraviolet and visible ( UV-Vis ) spectroscopy show that the LbL technique leads to linear growth of self assembled films. Characterizations with cw-PA reveal that there is charge photogeneration with good efficiency for both types of LHC s. The photogenerated charges present average lifetime in the range 100-200 µs with predominantly bimolecular recombination. Regarding to charge photogeneration, LHC s based on PDI-PEI : P3KHT are found to be less efficient than those based on P6N : P3KHT . However, results from photocurrent ( PC ) measurements reveal that the photogenerated charges in LHC s based on PDI-PEI : P3KHT are more efficiently organized in aligned dipole configuration than those in LHC s based on P6N : P3KHT , indicating that PDI-PEI diffuses less into the macromolecules of P3KHT than P6N . These results for the LHC s and SURMOFs show that cw-PA is a powerful characterization technique for organic electronic devices, in combination with other electric characterization tools.