>Magister Scientiae - MSc / Environmentally friendly photovoltaic devices make use of solar radiation as the energy source to generate electricity. Organic solar cells (OSCs) have been making headway in the last decade due to their cost-effectiveness and potential application in flexible devices. One of the disadvantages of OSCs is the short lifetime of the charge carriers, where the various interfaces that are present in the material play a significant role. In the inverted organic solar cell (IOSC), electrons are injected into the transparent conducting oxide, whereby the electrode alignment is reversed compared to the conventional structure. Nanosized zinc oxide (ZnO) thin-films with nanoridges/ripples embedded on the surface of the thin-film can be used as an electron transport/hole-blocking layers in inverted organic solar cells to enhance light-capturing by the active layer of the solar cell.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第17911号 / エネ博第283号 / 新制||エネ||59(附属図書館) / 30731 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 八尾 健, 教授 石原 慶一 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19007号 / 工博第4049号 / 新制||工||1623(附属図書館) / 31958 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 赤木 和夫, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Research in recent years on novel materials in organic solar cells (OSCs) have contributed to a rapid advancement in OSC efficiency. Here, OSCs with the well-studied organic semiconductors poly(3-hexylthiophene):[6,6]-phenyl C60-butyric acid methylester (P3HT:PCBM) in a bulk heterojunction structure were prepared to establish a baseline procedure for fabrication and spin-sensitive spectroscopy. Spin-sensitive spectroscopy can be used to probe the spin-dependent processes and loss mechanism in OSCs. Understanding the microscopic processes enables research targeting loss mechanisms directly, which opens up for higher efficiency OSCs. Measurements with continuous wave electrically detected magnetic resonance (cwEDMR), continuous wave electron paramagnetic resonance (cwEPR) and transient (tr)EDMR were set up and followed by an initial study on the spin-dependent processes and their influence on the photocurrent. Signals from spin-dependent processes in the samples were seen for the three experiment series carried out, and well-functioning OSCs with consistent results were prepared. This thesis and the presented baseline fabrication and experimental setup procedures provide with valuable learnings for future research in the group AG Behrends enabling fabrication and spin-sensitive studies on novel materials in OSCs. It was found that post-processing annealing at 120 C for 5 min reduces S-shape behaviour in current-voltage curves, and over all improves poor current-voltage characteristics of the OSC samples fabricated. Further, influence from PEDOT:PSS was seen in cwEPR spectroscopy, indicating the presence of traps or free radicals in the PEDOT:PSS. In cwEDMR spectroscopy of the OSCs it was shown that the spin processes of bias-induced and photo-induced charge carriers influence the photocurrent in the same way. Finally, the authors suggest that results from spin-sensitive spectroscopy of degraded OSCs cannot be applied to non-degraded OSCs.

No description available.

No description available.

In recent years, non-fullerene acceptors (NFAs) have attracted enormous interest in the field of organic solar cells (OSCs), they improve power conversion efficiency (PCE) compared to the classical fullerene acceptor. In this work, OSCs based on PBDB-T as the donor material and the very well-known NFA ITIC, along with its fluorinated and chlorinated derivatives (IT-2F, IT-4F, IT-2Cl, IT-4Cl) were fabricated to investigate the effect of the halogenation end group on the photovoltaic parameters. Optical characterization reveals that both chlorination and fluorination are effective in downshifting the molecular energy levels and redshifting the absorption spectra, which results in higher Jsc but lower Voc compared to pristine ITIC. In addition, the halogenated ITIC device exhibited enhanced FF and PCE. Various optoelectronic techniques were also used to investigate the charge recombination dynamics and charge extraction process. It has been found that (IT-2F, IT-2Cl) show suppressed monomolecular recombination compared to di-substituted NFA (IT-4F, IT-4Cl). Furthermore, fluorinated ITIC has a longer charge carrier recombination lifetime but a lower carrier extraction rate. Lastly, the best-performing device from the preceding component mixtures PBDB-T:IT-2F was exposed to thermal annealing at different stages of the fabrication process to investigate how annealing affects the photovoltaic parameters. According to our findings, both post and 2-stage annealing improve FF and PCE, but the latter is even more beneficial. In further studies, the annealing effect on the HTL layer (MoOx) has also been investigated. Annealing improved the MoOx’s work function, resulting in higher internal electric field that thereby facilitated hole extraction, as demonstrated by TPC where 2-stage annealed devices exhibited a faster carrier extraction rate.

The objective of this study is to observe how changing amount or ratio between dried mixes of poly-methyl-methacrylate and poly-styrene change the surface appearance, and how the results might inform future design of Organic photovoltaic cells, whom are based on polymer mixtures and heavenly dependent on the arrangement of polymers. An atomic force microscope was used on glass surfaces coated in a poly-methyl-methacrylate/poly-styrene matrix and dried from either dichloromethane or ethyl-acetate to determine surface appearance. Differing polymer mass-fractions or molecular weights matrices were assessed to determine their potential effects on surface domain and roughness size. In addition, an evaporation test was conducted to compare the solvent’s vapour pressure and how rates of evaporation change with the different polymer blends in solution. The result of atomic force microscope analysis pointed towards about 70% larger domains for ethyl-acetate than dichloromethane in general for the molecular weights samples, within the general trend another could be parsed; poly-styrene length is the major factor compared to poly-methyl-methacrylate for increasing domain size. When it came to mass-fractions, both poly-styrene static and poly-methyl-methacrylate static with varying poly-methyl-methacrylate and poly-styrene respectively was examined. Therein it was found that a fraction increases of poly-methyl-methacrylate shrunk domain size about 10% while increasing poly-styrene fractions grew domain sizes about 32%. However, unlike molecular weights, where surface roughness increased with longer polymers regardless if that was poly-methyl-methacrylate or poly-styrene, mass-fractions roughness always dropped whenever fraction size disparity grew, possibly due to homogenisation of the surface. In conclusion shorter and in excess polymers of poly-methyl-methacrylate produced smaller domains when paired with similar length poly-styrene in an accommodating solvent of high vapor pressure. Although lower vapour pressures are also feasible but at the cost of generally larger domain sizes.

No description available.

No description available.