Physical and Chemical Interface Modification to Improve Device Characteristics of AgNW-Based Optoelectronic Devices

Flexible and transparent electrodes are essential to fabricate flexible optoelectronics such as LCD, OLED, OPV. Silver nanowire (AgNW)-based electrodes are considered as the most suitable alternative transparent electrode to replace ITO electrode and achieve flexible devices due to good electrical, optical, mechanical properties. Here, we investigated major mechanism to improve electrical property of AgNW-based electrode by introducing sol-gel ZnO layer. The electrical properties are improved by two major effects, which are electrical bridge effect and the decrease in interconnection resistance due to capillary force. We introduced ZnO layer to AgNW-based electrode with different architecture to decouple each effect. All architectures with ZnO layer had lower resistance than reference electrode without ZnO layer. In particular, the architecture in which the electrical bridge effect is dominant had lower resistance than the architecture in which the decrease of interconnection resistance due to capillary force is dominant. To theoretically calculate each effect on the resistance of electrode, we constructed the equivalent circuit based on electrical path in each architecture. Similar to experimental results, the electrical bridge effect rather than the decrease of interconnection resistance due to capillary force affected the improvement of the electrical properties of the AgNW-based electrode. To apply such AgNW-based electrode to optoelectronics, patterning process is essential. However, general patterning process such as photolithography is too complex and expensive. So, to fabricate AgNW-based optoelectronic devices economically and ecofriendly, we developed the novel patterning process for AgNW-based electrode by controlling the adhesion between AgNW and substrate. Particularly, when using flexible substrate such as PET as a bottom substrate, we achieved to simultaneously pattern AgNW exposed and embedded electrodes through selective surface modification. In addition, we figured out the critical adhesion to success patterning process by exploring various substrates and AgNWs with different properties. Then, AgNW-exposed and embedded electrodes were applied to various optoelectronics such as OPV, LC cell, and each device showed well-operating performance. But, when fabricating an organic solar cell, it showed a low power conversion efficiency. So, to improve its power conversion efficiency, we fabricated the microlens arrays of various diameter (0.5µm~10µm) and confirmed that the optical properties and PCE can be dramatically increased with microlens array. When we examined optical properties by UV-VIS spectroscopy, the total transmittance was almost the same regardless of the diameter of microlens. But, the specular transmittance was sharply decreased with increasing diameter of microlens. It indicated that the dispersive light increased with increasing diameter of microlens. Because dispersive light has longer optical path, the increase of PCE was attributed to the increase of the probability of light absorption and excitons generation in photoactive layer. In addition, experimental performance of OPVs with microlens array was well matched with theoretically expectation which was calculated from optical properties of the microlens arrays.