Construction of Transparent Cellulose-Based Nanocomposite Papers and Potential Application in Flexible Solar Cells

Flexible electronics are developing rapidly due to promising applications in displays, sensors, and energy conversion fields. For biodegradable, lightweight, and flexible thin film electronics to be explored, O-(2,3-Dihydroxypropyl) cellulose (DHPC) was synthesized by homogeneous etherification of cellulose in 7 wt % NaOH/12 wt % urea aqueous solution without extra catalyst. DHPC exhibited a high level of transparency, outstanding ductility, and good adhesiveness but poor mechanical properties. Thus, stiff tunicate cellulose nanocrystals (TCNCs) were introduced to construct tough nanocomposite papers. The reinforcement of nanocomposite papers was well predicted by a percolating model, indicating the formation of the network of TCNCs. On the basis of the excellent interfacial compatibility between TCNCs and DHPC, supported by atomic force microscope mapping, the nanocomposite papers exhibited smooth surface, high transparency, as well as satisfactory mechanical properties, which were suitable for the construction of flexible polymer solar cells. Tin-doped indium oxide could be directly coated on the adhesive transparent paper without any glue as electrode, and the power conversion efficiency of the resulting flexible inverted polymer solar cells was 4.98%, suggesting its potential application as biodegradable and wearable electronics or optoelectronics. This work is important for developing clean energy by using sustainable materials derived from renewable resources.