Fundamental Study on Highly Transparent Films for Solar Cell Substrate Using Nanocellulose

Abstract

In this study, we conducted a fundamental investigation on the manufacturing of transparent films suitable for solar cell substrates using nanocellulose prepared from non-woody pulps. Cellulose nanocrystals (CNCs) were prepared using paper mulberry pulp, while quaternized cellulose nanofibers (Q-CNFs) and carboxymethylated cellulose nanofibers (CM-CNFs) were prepared using cotton lint mixed pulp (CLMP). The films were manufactured by adjusting the size of CNCs, zeta potential of CNFs, and CNC/CNF mixing ratio using a combined technique of vacuum-assisted and evaporation-induced selfassembly methods,depending on the type of nanocellulose. The thickness, transparency, and b* of the films were measured to determine the optimal manufacturing conditions. The films prepared with only the smallest CNC (Short-CNC) showed higher transparency than those prepared with a mixture of Short-CNC and the longest CNC (Long-CNC). The transparency of the films prepared with Short-CNC and Q-CNF decreased because of the flocs induced by the attractive interaction between them. Meanwhile, the films prepared with Short-CNC and CM-CNF showed high transparency because Short-CNC and CM-CNF comprised negative charges. The CNC/CM-CNF mixing ratio of 5:5 resulted in the highest transparency of the film. Therefore, highly transparent films suitable for solar cell substrates can be manufactured by combining CNCs and CM-CNFs.