| Thin-film solar cells are promising alternatives to their crystalline siliconwafer-based counterparts due to the cost reduction and shorter energy-paybacktime. Moreover, thin film solar cells constructed on flexible substrates offer newopportunities for building-integrated photovoltaics (PVs) and portable powersources because of the light-weight, mechanically flexibility. It is known that theperformance of PV devices largely rely on their optical absorption and carriercollection dynamics in the devices. Normally, the absorption layers in thin filmPVs bear poor transport properties, with the short carrier diffusion length. Usingthinner absorbing layers will improve effective carrier transport, butsimultaneously induce insufficient light absorption. In this regard, designingstate-of-the-art light harvesting structures has become an intriguing topic tosolve the fundamental incompatibility between electronics and optics in the PVdevices. Great endeavors have been devoted to improve the light harvestingcapabilities in limited thin film thickness. Based on these designs, we propose anovel patterned substrate that fabricated by low-cost anodization process, whichcan improve the absorption of devices effectively. In addition, a nanopillarmembrane was coated on the device as an anti-reflective skin, which aims tofurther improve the absorption of the devices. In detail, we firstly fabricated and characterized patterned titaniumsubstrate; secondly, fabricated and characterized anti-reflective nanopillarmembrane that made of polydimethylsiloxane (PDMS); thirdly, we tried toemploy the patterned substrate and anti-reflective nanpillar membrane inhydrogenated amorphous silicon (a-Si:H) solar cells, with the addition of somesimulations using Finite Difference Time Domain (FDTD) method; finally, wepropose a scheme for the using of patterned titanium substrate andanti-reflective nanopillar membrane in organic thin-film solar cells.1. The patterned titanium substrate was fabricated using the anodizationprocess. Firstly, in the process of the anodization, the voltage was applied as170V, and the pitch size of the obtained TiO2nanotubes was about600nm; secondly,TiO2nanotubes were removed by3M magic tape or ultrasonic cleaning method,and the left substrate with nanodent structure was the patterned substrate.Moreover, different anodization time has been studied, and the result shown thatthe shape of the nanodent was changing from regular hexagon to circle.2. The fabrication of anti-reflective PDMS nanopillar membrane. Firstly, wefabricated the V-shaped anodic aluminum oxide (AAO) using multi-stepanodization method; secondly, the PDMS was pouring onto the surface of theV-shaped AAO thin film, and the residual bubble was removed by vacuuming inthe O2plasma cleaning machine; thirdly, the PDMS with the AAO mold wasdried in the drying oven for three hours at60centigrade degree; finally, thePDMS membrane was tearing off the AAO mold, and the inverted V-shapestructure will leave on the surface of the PDMS, which was called nanopillarstructure.3. The patterned titanium substrate and anti-reflective PDMS nanopillarwere applied in the a-Si:H solar cells. The patterned structure has shownexcellent light trapping properties, while the PDMS nanopillar membrane hasreduced the light reflecting back to the air effectively. In detail, in contrast to theplanar device, the efficiency of the patterned device has enhanced to37.6%. In addition, the dual-interfacial patterned device also shows significant flexibleproperties. Especially, the performance of the device only suffer a slightlydecrease when the bending angle reaches to120degree and the bending cyclesreaches to10000times. For the further study of the enhancement mechanism ofthe patterned structure, some simulations were adopted using the FDTD method.In the simulation results, some optical modes were found as waveguide modesand plasmonic waveguide modes that can enhance the propagation length of thelight and improve the light trapping effect in the device.4. In the basis of the study in the a-Si:H solar cells, we proposed anexperiment scheme for the using of patterned titanium substrate andanti-reflective nanopillar membrane in organic thin-film solar cells. |
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