|Title:||TCO-free and low-cost flexible perovskite solar cells|
|Advisors:||Zheng, Zijian (ITC)|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Perovskite solar cells
Solar cells -- Materials
Photovoltaic cells -- Materials
|Department:||Institute of Textiles and Clothing|
|Pages:||xxii, 133 pages : color illustrations|
|Abstract:||The newly emerging organo-metal halide perovskite solar cells (PSCs), which was developed a decade ago, represent one of the most promising photovoltaic techniques to compete with the currently-dominating Si solar cells in the future. PSCs are characteristic of some desirable features of high efficiency, low cost, lightweight, solution processability, and so forth. Importantly, PSCs possess intrinsically excellent flexibility, stemming from sub-micrometer photo-active perovskite materials thanks to their high photo-absorption capabilities. However, flexible PSCs employing the transparent conductive oxides (TCOs) as the front electrodes often encounter severe device degradation during high degrees of mechanical deformation, as a result of the brittle TCOs. Although some transparent conductive materials based on polymers, carbons or metals have been extensively exploited to replace TCOs, many of them still suffer from inferior optoelectrical properties and/or high fabrication cost. In view of these challenges, TCO-free highly-flexible PSCs will be developed with the objectives of obtaining a high device efficiency and a low material cost at the same time in this thesis. Firstly, three types of transparent electrodes are developed by using metal grids (Au or Cu) or acid-treated PH1000 film on the flexible PET substrate. Key parameters of the metal grids and the PH1000 film have been investigated for the sake of the desired optoelectrical features. These TCO-free transparent electrodes could demonstrate satisfactory performance suitable for PSCs application. More interestingly, their high mechanical durability is potentially favorable for fabricating highly-flexible PSCs.|
Next, flexible PSCs are fabricated based on the hybrid transparent electrode of Au grids and a thin layer of the conductive polymer PEDOT:PSS. The flexible device shows a champion PCE of >11%, which is comparable to the reference device on the rigid Glass/ITO substrate. Such flexible PSCs could maintain 90% and 85% of their initial efficiencies after being bent for 1000 times at a radius of 10 mm and 6 mm, respectively. Then, Cu are used both as the bottom transparent electrode as well as the top rear electrode for flexible PSCs in order to reduce the materials cost. The low-cost inorganic copper-doped nickel oxides (Cu:NiOx) are also studied and prove to be an efficient and stable hole-transporting layer (HTL) material, after treatment with methanol (MeOH). As-fabricated flexible PSCs show a champion efficiency of ~14%. When bent a radius of 5 mm for 1000 times, PCE of as-fabricated PSCs decayed only by ~10%, with negligible changes in Voc and FF. Lastly, PH1000 films deposited on PET are also exploited as the flexible transparent electrodes, upon treatment with a mild acid, methanesulfonic acid (MSA). The smoother surface and the higher optical transmittance in comparison to the metal grids-based hybrid transparent electrodes make MSA-PH1000 film a promising TCO alternative in the application for flexible PSCs. In conclusion, TCO-free transparent electrodes based on metals or polymers have been fabricated and successfully applied in the high-performance flexible PSCs, in combination with some inexpensive materials. This work may provide some insights as to how to fabricate low-cost and high-performance flexible electronic devices.
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