Fabrication of cellulose-elastomer films for optoelectronics

One of the main ways of improving the sustainability and recyclability of solar cells is the implementation of biomaterials. Cellulose has become a material of interest in the photovoltaic (PV) industry since it has excellent optical, and mechanical properties besides its biodegradability and biocompatibility. However, cellulose often needs to be modified with other polymers to maximize the mechanical and optical properties and enhance its use in different applications. In this study, a combination of cellulosic materials and an elastomer in film structures was investigated to replace the glass substrate of solar cells. Cellulose nanofiber (CNF) and cellulose acetate (CA) were combined with polydimethylsiloxane (PDMS) in different approaches and the compatibility of PDMS with cellulosic materials was investigated. The aim was to achieve transparent and flexible substrates with good optical and mechanical properties. CNF films were prepared by a pressure-assisted filtration system, and they later went through a solvent exchange process. After this step, two different methods were followed to obtain CNF:PDMS composite structure: PDMS immersing and vacuum infiltration. High transmittance and haze were obtained with vacuum infiltrated CNF:PDMS composite films, however tensile testing results showed that the CNF:PDMS composite films obtained from immersing method have better mechanical properties. To investigate the composite structures, scanning electron microscopy (SEM) analysis was completed. PDMS filling in the porous structure of the CNF films was achieved via the vacuum infiltration method. As a complementary research approach, layer-by-layer deposition of CA:PDMS films were completed by spin coating, and four layers were assembled to obtain a film structure. However, it was challenging to control the thickness of CA films, and the compatibility of CA and PDMS was not successful due to PDMS surface properties. High transmittance and low haze properties were obtained with poor mechanical properties. Further research is needed for this approach to achieve compatibility between these materials