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 trade-off 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 displays both ultrahigh optical transparency (∼ 96%) and ultrahigh 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.
Paper, as an inexpensive substrate for flexible electronics and energy devices, has garnered great attention because of its abundance, biodegradability, renewability and sustainability. However, the intrinsic opacity and higher roughness of regular paper greatly restricts further applications. One promising method is to use cellulose nanofibers (CNs) to fabricate nanopaper with a high optical transmittance and excellent smoothness, but there are still some challenges facing nanopaper substrates, such as high-energy consumption to extract nanofibers and the time-consuming process to prepare nanopaper. We design a bilayer hybrid paper using unbeaten wood fibers and CNs with a papermaking technique, which achieves a high optical transmittance and superior smoothness while remaining less expensive than nanopaper and useful as a writable surface. The first transparent paper touchscreen with an excellent anti-glare effect in bright environments is demonstrated using our novel transparent and conductive hybrid paper as the flexible electrode.
Next-generation electronic technology requires the use of advanced energy storage devices with integrated functionality to fulfill key application requirements. A smart supercapacitor shares the same electrochemical processes as a conventional energy storage device in addition to electrochromic functionality. It can sense the energy storage level and can display it in a noticeable manner, which results in added convenience to everyday applications. In this study we have developed a smart supercapacitor that uses tungsten oxide nanograin thin film to provide the combined advantages of energy storage and electrochromism. The nanostructured tungsten oxide is dark blue in the charged state and becomes transparent in its discharged state; and it has a specific capacitance of 228 Fg −1 at 0.25 Ag −1 with a quite large potential window of 1.4 V. It is highly durable, exhibits good electrochemical stability over 2000 cycles, retains a significant charge storage of 75%; and exhibits a high coloration efficiency of ~170 cm 2 /C with an optical modulation of 82%. The smart-supercapacitor fabricated with this material exhibits a superb combination of 2 energy storage and electrochromic features in one device to monitor the energy storage level through visible changes in color.
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