Fabrication processes of carbon nanomaterial composites and their applications for conductive materials in organic solar cells

Abstract

Organic solar cells (OSCs) have received considerable attention as a clean renewable energy source due to their advantages of being lightweight, cost-effective, highly flexible and mass producible via simple solution processing. In spite of these advantages, the commercialization of OSCs is still limited due to their low power conversion efficiency (PCE). The low charge mobility of organic materials increases the chance of carriers recombining or dissipating during the charge transport and collection states; as a result, the PCE is low. One way of overcoming this problem is to introduce carbon nanomaterials with high charge mobility, such as carbon nanotubes (CNTs) and graphene. Incorporation of CNTs and graphenes into OSCs can enhance the device performance by providing highly conductive pathways for carrier transport or collection. In spite of the large potential of CNT and graphenes as charge transport or collection materials in OSCs, PCEs of these devices are still lower than conventional bulkheterojunction OSCs. Dispersion and band gap engineering of CNT and graphene nanocomposites should be considered for highly efficient OSCs. In this research, a systematic study of CNT and graphene nanocomposites was proposed considering the characteristics of each of layers in OSCs. The OSC consists of the photo-active layer and charge transport layer excluding the electrodes, and the charge transport layer is also classified into the hole and electron transport layer. CNT and graphene nanocomposites were designed considering the characteristics of each of layers in OSCs; hole transport layer, electron transport layer and photo-active layer. First, for hole transporting layer in OSCs, CNT/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate), (PEDOT:PSS) nanocomposites were designed. The key factor for design of CNT/PEDOT:PSS nanocomposites is the homogeneous dispersion of CNTs by non-covalent functionalization for high optical transmittance and electrical conducti...