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Title: Highly flexible solution-processed solar cells
Authors: Zhang, Yaokang
Degree: Ph.D.
Issue Date: 2018
Abstract: Flexible thin-film solar cells such as organic solar cells (OSCs), dye-sensitized solar cells (DSSCs), perovskite solar cells (PSCs) have attracted tremendous attention in recent years. Such solar cells are easy to fabricate and potentially high-efficient, and they can be flexible once fabricated on flexible substrates. However, there are two major issues for most of the reported thin-film solar cells. First, the fabrication of these solar cells requires high temperature or vacuum deposition technologies, which are neither low-cost nor scalable. Second, these solar cells employ transparent conducting oxides (TCOs) as transparent electrodes, which are not suitable for flexible applications due to their mechanical brittleness. Recently, there has been some reports on fabricating thin-film solar cells by low-cost solution-based roll-to-toll (R2R) process, but the solar cell efficiency was too low for practical applications. In this thesis, these issues are tackled by developing and optimizing of several solution-based deposition technologies through chemical approaches. First, the chemical fabrication of Cu electrodes by polymer-assisted metal deposition (PAMD) was investigated. PAMD is an advanced electroless deposition (ELD) technology for metal thin films. Multiple examples of patterned Cu electrodes which were obtained by either patterning the catalytic precursor (PCP) or patterning the functional polymer (PFP) were demonstrated. The advantages and disadvantages of these two approaches were discussed.
Second, the application of nitric acid annealed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (n-PEDOT:PSS) on semi-transparent perovskite solar cells (st-PSCs) was studied. The optical and electrical properties of n-PEDOT:PSS were characterized by multiple approaches to evaluate its eligibility as transparent electrode. Then, the n-PEDOT:PSS electrodes were applied on st-PSCs as both top electrodes and bottom electrodes. Highly efficient st-PSCs based on n-PEDOT:PSS electrodes were fabricated, and they were integrated with monocrystalline Si (c-Si) solar cells to form 4-terminal tandem solar cells. Furthermore, highly flexible st-PSCs were fabricated on polyethylene terephthalate (PET) and polyimide (PI) substrates. Such examples indicated the superior flexibility of n-PEDOT:PSS electrodes over the traditional TCOs. Third, all-solution-processed ultrathin OSCs were designed and fabricated. The OSCs combined solution-processed Cu electrodes and PEDOT:PSS electrodes together on ultrathin PI substrates, which were also fabricated by solution-based coating technique. The excellent flexibility of the OSCs were verified by repeated stretch-compress test of the OSCs on pre-stretched elastomers. In addition, BHFs that can improve the light absorption of OSCs and PSCs were fabricated by one-step soft lithography molding. The optical transmittance and haze effect of the BHF was studied in detail, while the anti-reflection and light-trapping effects of BHF was characterized by the current density-voltage (J-V) and external quantum efficiency (EQE) measurements of the solar cells. In conclusion, highly flexible PSCs and OSCs were fabricated by fully-solution-based processes. The solution-processed Cu and PEDOT:PSS electrodes were highly compatible with flexible PSCs and OSCs. Such solution-processed PSCs and OSCs showed satisfactory efficiency as well as excellent mechanical flexibility. In principle, these solution-based strategies for PSCs and OSCs are also versatile for the fabrication of other electronic devices based on metal or polymer conductors. Hence, this work is believed to have great impact on the fields of flexible energy harvesting/storage devices, displays, sensors, and etc.
Subjects: Hong Kong Polytechnic University -- Dissertations
Solar cells
Pages: xviii, 115 pages : color illustrations
Appears in Collections:Thesis

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