Scalable, highly transparent paper with microsized fiber

Abstract

Solar cell substrates require high optical transparency, but also prefer high optical haze to increase the light scattering and consequently the absorption in the active materials. Unfortunately there is a tradeoff between these optical properties, which is exemplified by common transparent paper substrates exhibiting a transparency of about 90% yet a low optical haze (<20%). In this work we introduce a novel transparent paper made of wood fibers that display both ultra-high optical transparency (˜96%) and ultra-high haze (˜60%), thus delivering an optimal substrate design for solar cell devices. Compared to previously demonstrated nanopaper composed of wood-based cellulose nanofibers, our novel transparent paper has better dual performance in transmittance and haze, but also is fabricated at a much lower cost. This high-performance, low-cost transparent paper is a potentially revolutionary material that may influence a new generation of environmentally friendly printed electronics.

What is claimed is: 
     
         1 . A transparent paper comprising:
 an optical transparency of at least 96%; and   an optical haze of at least 60%.   
     
     
         2 . The transparent paper of  claim 1  further comprising;
 a cell wall; 
 a plurality of wood fibers in the cell wall, 
 wherein the plurality of wood fibers comprise a primary layer and a secondary layer, the primary layer having a thickness of 0.1-0.2 μm and the secondary layer having a thickness of about 1.0-5.5 μm. 
 
     
     
         3 . The transparent paper of  claim 2  wherein the wood fibers comprise a plurality of microfibrils, the plurality of microfibrils being randomly oriented in the primary layer and helically wound in a fiber axis of the secondary layer. 
     
     
         4 . The transparent paper of  claim 2  wherein the wood fibers have a diameter of 5 nm to 20 nm, a tensile strength of about 105 MPa, and a toughness of about 1.88 J/M 3 . 
     
     
         5 . A method of making transparent paper comprising the steps of:
 (a) treating bleached sulfate softwood pulp with a TEMPO-Oxidized system comprising;
 (i) dispersing 5 g of wood fibers into 1% pulp with deionized water to make wood pulp; 
 (ii) adding TEMPO and sodium bromide (NaBr) separately into the wood pulp; 
 (iii) stifling the mixture continuously to form a uniform suspension; 
 (iv) titrating the uniform suspension with sodium hypochlorite (NaClo); 
   (b) filtrating the uniform suspension; and   (c) fabricating a transparent paper from the filtrated uniform suspension.   
     
     
         6 . The method of making transparent paper of  claim 1  wherein the bleached sulfate softwood pulp is extracted from the southern yellow pine without beating or refining. 
     
     
         7 . A solar cell application comprising:
 a laminated transparent paper, the laminated transparent paper comprising an optical transparency of at least 96% and an optical haze of at least 60%.   
     
     
         8 . The solar cell application of  claim 1 , wherein the laminated transparent paper further comprises:
 a cell wall;   a plurality of wood fibers in the cell wall,   wherein the plurality of wood fibers comprise a primary layer and a secondary layer, the primary layer having a thickness of 0.1-0.2 μm and the secondary layer having a thickness of about 1.0-5.5 μm.   
     
     
         9 . The solar cell application of  claim 8 , wherein the wood fibers comprise a plurality of microfibrils, the plurality of microfibrils being randomly oriented in the primary layer and helically wound in a fiber axis of the secondary layer.