SCANNING PROBE MICROSCOPY STUDY ON NANOSTRUCTURED MATERIALS IN ORGANIC AND PEROVSKITE OPTOELECTRONIC DEVICES

Abstract

Since discovery of electrical conductivity in organic substances, organic optoelectronics have been developed and diversified for several decades. Studies on organic optoelectronics and organic-inorganic hybrid optoelectronics, including organic light emitting diodes (OLEDs), organic solar cells (OSCs) and perovskite solar cells (PSCs) have enlarged its application to practical industries. In order to understand charge carrier behaviors in multi-stacked thin film devices of optoelectronics, nano-scale characterization is important to investigate practical excitonic reaction. Moreover, by adapting nanomaterials and nano-scaled layers onto devices, their performance is able to be improved on efficiency and stability.<br/> In this thesis, we adapt nanomaterials and nano-scaled layers on organic and perovskite optoelectronic devices. Flexible and efficient OLEDs are fabricated using dual-scale AgNWs electrode. ZnO NRs array as electron transporting layer and Liq interlayer for work function matching is applied on excitonic solar cells such as organic solar cells and perovskite solar cells.<br/> First, we fabricate flexible electrode using dual-scale AgNWs which is made by mixing short/thin AgNWs and long/thick AgNWs. Dual-scale AgNWs have excellent properties as flexible electrode for organic optoelectronics which includes conductivity, transmittance, roughness and coverage. Rouhness and coverage is analyzed through AFM and EFM. The green emission phosphorescent organic light emitting diodes is fabricated onto the electrode and compared to mono-scale AgNWs electrode. The OLEDs based on dual-scale AgNWs are superior to the others and there is no spectral difference in luminescence. <br/> Organic solar cells are fabricated on vertically grown ZnO NRs array as electron transporting layer. ZnO NRs are fabricated using facile method of hydrothermal synthesis with a linearly controllable length profile. There is orientation increment of ZnO NRs proportional to length after germination. ZnO NRs with different lengths are utilized as efficient electron transport layers in organic solar cells. The length of ZnO NRs is optimized under trade-off relationship in charge collection and UV absorption.<br/> And finally, nano-scaled layer of perovskite and Liq is characterized to improve photovoltaic performance and stability. The physical process of perovskite degradation is investigated through the FFM and conductive AFM. The perovskite fabricated under humid air and argon atmosphere is compared and it is found that degradation of perovskite by moisture is initiated from local islands. Liq has effective work function tunability to electrode for optoelectronic devices. Its coverage onto PCBM electron transporting layer is increased by deposition thickness but the uniformity is deteriorated after full coverage. The current enhancement through the Liq interlayer is measured through conductive AFM and its potential change is measured through SKPM.<br/> In conclusion, this thesis proposes the practical utilization of nanomaterials and nano-scaled layers to improve flexibility, performance and stability of excitonic optoelectronic devices. These approaches and versatile measurement techniques in film-level and device-level characterization of individual cell are expected to be applicable to other researches which need nanoscale investigation and fabrication. <br/>