High Efficiency and Wide Color Gamut Liquid Crystal Displays

Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5× increment in spatial resolution, 2× brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4× on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to ±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

DESIGN AND MICROFABRICATION OF EDGE-LIT OPTICAL LIGHT CURTAINS

Plastic optical light guides can be used for a variety of interior and exterior vehicle light curtains such as cabin illuminators and automotive tail lights. The edge-lit wave guide is an optically transparent substrate coupled with one or more energy efficient light emitting diodes (LEDs). The light rays from the source travel through the substrate based on the principle of total internal reflection. If a surface of the optical wave guide is patterned with optical microstructures then the light rays will scatter and refract throughout the medium, primarily exiting opposite to the patterned surface. Uniform illumination over this active surface region is a function of the individual optical microstructure\u27s shape and the spatial distribution of the microstructures. The goal of this research is to investigate the light dispersion characteristics in both smooth and micro-patterned optically transparent substrates, and utilize optical simulation software to develop viable design approaches for fabricating small and medium sized light curtains. The study first identifies an appropriate optical microstructure (i.e. cylindrical indentations) that can be reliably imprinted on the surface of an optically transparent polymethyl-methacrylate (PMMA) substrate using a multi-axis micromilling machine. The optical simulation software Light Tools is then used to determine the most appropriate microstructure radius and spatial positioning of elements for uniform light distribution. The key design and fabrication parameters for near optimal performance are summarized and used to establish the process plan for the high-speed precision micromilling operations. Experiments are performed on several 100 mm x 100 mm x 6 mm polymer light guide panels (LGPs) including a customized design with a hexagonal arrangement of microstructures. Both interior and boundary regions of the sample LGPs are investigated for intensity distribution, optical transmission efficiency, and light loss. Although the experiments involve relatively small flat PMMA LGPs, the optical design and microfabrication methods can be readily extended to larger surface areas or curved optically transparent polymer substrates for contoured light curtains

Modern lithographic techniques applied to stereographic imaging

The main aim of the research has been to produce and evaluate a high-quality diffusion screen to display projected film and television images. The screens have also been found to effectively de-pixelate LCD arrays viewed at a magnification of approximately 4x. The production process relies on the formation of localized refractive index gradients in a photopolymer. The photopolymer, specially formulated and supplied by Du Pont, is exposed to actinic light through a precision contact mask to initiate polymerization within the exposed areas. As polymerization proceeds, a monomer concentration gradient exists between the exposed and unexposed regions allowing the monomer molecules to diffuse. Since the longer polymer chains do not diffuse as readily, the molecular concentration of the material, which is related to its refractive index, is then no longer uniform. The generation of this refractive index profile can, to some extent, be controlled by careful exposure of the photopolymer through the correct mask so that the resulting diffusion screen can be tailored to suit specific viewing requirements. [Continues.

Quantum dot polymer composite materials for light management in optoelectronic devices

This dissertation will highlight a path to achieve high conversion efficiency of optoelectronic devices, including photovoltaic concentrators and LED display modules. Semiconductor nanocrystals, also known as quantum dots (QDs), serve as the pivotal luminescent materials in these devices. A quantum dots encapsulation method was developed here to homogeneously disperse QDs in a transparent polymer matrix, enabling high optical quality devices and thorough investigation of light material interactions. A luminescent solar concentrator (LSC) typically consists of a luminophore embedded in a polymer sheet with a high-performance solar cell attached at the side. In such a device, sunlight is absorbed in a luminophore, emitted into the waveguide modes of the polymer sheet, and directed to a photovoltaic cell where it is absorbed and converted to electricity. Since the area of the polymer sheet is greater than the area of the photovoltaic cell, concentration of the solar photon flux is achieved. Approaching high concentration ratio will require a luminophore with large Stokes Shift, high quantum yield, minimal overlap between absorption and emission, and a narrow emission spectrum. We have examined the performance of LSCs utilizing CdSe/CdS core-shell QDs, with significantly reduced absorption-emission overlap and long propagation distances in the waveguide. Furthermore, a distributed Bragg reflector dramatically mitigates the negative impact of scattering in the waveguide, allowing efficient photon collection and concentration ratio. White-light LED is achieved by using a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light. However, tradition yellow phosphors suffer from low color rendering index due to the broad emission spectrum of the phosphors. QDs have been proposed as better candidate than traditional yellow phosphors due to their narrow and tunable emission spectrum, and wide absorption spectrum in the UV-blue spectrum range. We have fabricated QD-polymer thin films as color conversion layers on blue LED via different methods, including spin-coating, drop casting and electrohydrodynamic jet printing. The polymer surface has been incorporated with nano-sized features to create photonic crystal structure. Up to 8 times QD excitation and emission enhancement have been demonstrated. We have also designed and fabricated QD-polymer based concentrating cavity on blue LED that acts both as color conversion layer and light concentrator. Distributed Bragg reflector and sputtered silver have been used as reflectors surrounding QD-polymer thin film. The exterior of the concentrator cavity was coated with black absorber to suppress light reflection, and a small aperture in the center allows concentrated photons to exit. High power conversion efficiency and high ambient contrast have been achieved in module devices

High-Dynamic-Range and High-Efficiency Near-Eye Display Systems

Near-eye display systems, which project digital information directly into the human visual system, are expected to revolutionize the interface between digital information and physical world. However, the image quality of most near-eye displays is still far inferior to that of direct-view displays. Both light engine and imaging optics of near-eye display systems play important roles to the degraded image quality. In addition, near-eye displays also suffer from a relatively low optical efficiency, which severely limits the device operation time. Such an efficiency loss originates from both light engines and projection processes. This dissertation is devoted to addressing these two critical issues from the entire system perspective. In Chapter 2, we propose useful design guidelines for the miniature light-emitting diode (mLED) backlit liquid crystal displays (LCDs) to mitigate halo artifacts. After developing a high dynamic range (HDR) light engine in Chapter 3, we establish a systematic image quality evaluation model for virtual reality (VR) devices and analyze the requirements for light engines. Our guidelines for mLED backlit LCDs have been widely practiced in direct-view displays. Similarly, the newly established criteria for light engines will shed new light to guide future VR display development. To improve the optical efficiency of near eye displays, we must optimize each component. For the light engine, we focus on color-converted micro-LED microdisplays. We fabricate a pixelated cholesteric liquid crystal film on top of a pixelated QD array to recycle the leaked blue light, which in turn doubles the optical efficiency and widens the color gamut. In Chapter 5, we tailor the radiation pattern of the light engine to match the etendue of the imaging systems, as a result, the power loss in the projection process is greatly reduced. The system efficiency is enhanced by over one-third for both organic light-emitting diode (OLED) displays and LCDs while maintaining indistinguishable image nonuniformity. In Chapter 6, we briefly summarize our major accomplishments

디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 홍용택.일반적으로 제조 공정은 절삭 방식과 적층 방식으로 구분된다. 이 중에서 적층 방식 공정은 저비용 및 단시간으로 복잡한 형태의 구조를 만들 수 있어서 이에 대한 연구와 개발이 꾸준히 진행되어왔다. 특히 3D 프린팅은 적층 방식 공정 중에서 가장 대표적인 방법으로, 기계 부품 및 생체 기관 제조 등의 분야에서는 이미 상용화가 진행되고 있다. 하지만 전자 소자 및 광학 요소 분야에서의 3D 프린팅의 활용은 여전히 연구 개발 또는 시제품 제작 단계에 머무르고 있다. 특히 마이크로 렌즈, 컬러 필터 등이 3D 프린팅으로 응용할 수 있는 가장 가능성 있는 광학 요소로서 디스플레이 및 이미징 시스템에 널리 사용될 것으로 예상되지만 여전히 상용화를 위한 연구가 진행 중이다. 또한 3D 프린팅을 이용한 광학 요소의 제작은 소재, 길이 스케일, 형상 및 응용 방안 등에서도 제한이 많은 상황이다. 따라서 이러한 문제를 극복하기 위해서는 디스플레이 및 이미징 시스템에서의 3D 프린팅 된 광학 요소의 유용성을 확장해야 하며, 다음과 같이 세 가지 측면에서 향상된 성능을 달성해야 한다. 첫째, 다양한 방식의 3D 프린팅 방법을 통해 마이크로미터에서 센티미터까지 광범위의 길이 스케일을 가지는 구조물의 제작이 가능해야 한다. 둘째, 임의의 곡면, 계층적 구조 등 복잡한 형상의 구조물을 쉽게 제작할 수 있어야 한다. 셋째, 단단한 소재 대신 탄성체와 같은 소프트 소재를 이용하여 광학적인 기능을 용이하게 조절할 수 있어야 한다. 이와 같은 동기를 바탕으로 본 학위 논문에서는 디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발에 대한 내용을 보고한다. 3D 프린팅 기반 광학 요소를 매크로 스케일, 마이크로 스케일 그리고 매크로 및 마이크로 스케일이 혼합된 계층적 구조 등 세 가지 유형으로 분류하고 각각에 대한 응용 분야를 제시한다. 매크로 스케일의 광학 요소로는 가장 기본적인 요소인 렌즈와 거울을 선택한다. 렌즈는 공압식 디스펜싱 방법을 이용하여 실린드리컬 쌍 형태로 제작되었으며, 심리스 모듈러 평판식 디스플레이의 구현을 위해 적용된다. 또한 용융 적층 방식의 3D 프린팅으로 만들어진 몰드를 이용하여 거울을 제작하고, 이를 이용하여 심리스 모듈러 커브드 엣지 디스플레이를 구현한다. 이와 같이 모듈러 디스플레이의 이음새 부분에 3D 프린팅으로 제작된 렌즈 또는 거울을 부착하는 방식으로 화면을 심리스로 확장하는 기술을 제시하고, 다양한 형태의 디스플레이에 적용할 수 있는 가능성을 보여준다. 마이크로 스케일의 광학 요소로는 발광 다이오드에서 색 변환과 광 추출 기능을 동시에 나타내는 색 변환 마이크로 렌즈를 선택한다. 양자 점/광 경화성 고분자 복합체의 전기수력학적 프린팅을 통해 양자 점이 내장된 다양한 형태의 색 변환 마이크로 렌즈를 제작하며, 이를 청색 마이크로 발광 다이오드 어레이의 발광부 상에 적용하여 풀 컬러 마이크로 발광 다이오드 디스플레이로의 응용 가능성을 제시한다. 마지막으로 매크로 및 마이크로 스케일이 혼합된 계층적 구조의 광학 요소로서 디스펜싱 및 건식 러빙 과정의 조합으로 제작된 겹눈 형태를 모사한 렌즈 구조를 제시한다. 반구 형태의 매크로 렌즈를 디스펜싱으로 형성하고, 매크로 렌즈의 곡면 상에 단층의 마이크로 입자의 배열을 얻기 위해 건식 러빙 공정을 진행한다. 이러한 방식으로 형성된 계층적 구조가 소프트한 소재로 복제되어서 신축성을 가지는 겹눈 형태 모사 구조가 완성된다. 마이크로 렌즈 어레이는 매크로 렌즈의 표면을 따라 형성되고 리지드 아일랜드로 역할을 하여, 전체 계층적 구조에 기계적 변형이 가해져 매크로 렌즈의 모양이 변형되어도 마이크로 렌즈는 형상과 해상도, 초점 거리 등의 광학적 특성을 유지할 수 있다. 본 학위 논문은 3D 프린팅을 이용하여 다양한 형태와 스케일의 광학 요소를 제작하고 디스플레이 및 이미징 시스템으로의 여러 응용을 보여줌으로서 앞으로의 새로운 연구 및 개발 방향성을 제시하는 것을 주요 목적으로 한다. 3D 프린팅 설비의 단가가 낮아지고 정밀도 및 해상도가 높아지는 추세에 따라, 광학 요소를 쉽게 만들고 응용할 수 있는 맞춤형 광학 또는 스스로 구현하는 광학 분야가 변형 가능하고 멀티 스케일의 광학계로 점차 확대될 것으로 예상된다. 궁극적으로는 차세대 디스플레이 및 이미징 시스템에 필요한 광학 요소를 위한 기술의 저변을 넓히고, 이를 산업 전반에 응용할 수 있는 기반을 마련하고자 한다.Generally, the manufacturing process is divided into the subtractive (top-down) type and additive type (bottom-up). Among them, the additive manufacturing process has attracted a lot of attention because it can manufacture products with complex shapes in a low-cost and short-time process. In particular, three-dimensional (3D) printing is a representative method, which has already been commercialized in the field of mechanical components and biomedical organ. However, it remains in the research and development step in the field of electronic devices and optical components. Especially, although 3D printed optical components including microlens and color filter are expected to be widely used in display and imaging systems, it is still under investigation for commercialized products, and there are limitations in terms of materials, length scale, shape, and practical applications of components. Therefore, to overcome these issues, it is required for investigating and expanding the potential usefulness for 3D printed optical components in display and imaging systems to achieve better performance, productivity, and usability in three aspects. First, it should be possible to manufacture structures with a wide range of length scales from micrometer to centimeter through various 3D printing methods. Second, complex shapes such as free-from curved surfaces and hierarchical structures should be easily fabricated. Third, it is necessary to add functionality by manufacturing structures in which tunable functions are introduced using soft materials like an elastomer. Based on the above motivations, 3D printing-based customized optical components for display and imaging system applications are introduced in this dissertation. 3D printed optical components are classified into three types and their applications are showed to verify the scalability of 3D printing: macro-scale, microscale, and hierarchical macro/micro-scale. As macro-scale printed optical components, lens and mirror which are the most basic optical components are selected. The lens is fabricated by a pneumatic-type dispensing method with the form of a cylindrical pair and adopted for demonstration of seamless modular flat panel display. Besides, a seamless modular curved-edge display is also demonstrated with a mirror, which is fabricated from fused deposition modeling (FDM)-type 3D printed mold. By simply attaching a printed lens or mirror onto the seam of the modular display, it is possible to secure seamless screen expansion technology with the various form factor of the display panel. In the case of micro-scale printed optical components, the color-convertible microlens is chosen, which act as a color converter and light extractor simultaneously in a light-emitting diode (LED). By electrohydrodynamic (EHD) printing of quantum dot (QD)/photocurable polymer composite, QD-embedded hemispherical lens shape structures with various sizes are fabricated by adjusting printing conditions. Furthermore, it is applied to a blue micro-LED array for full-color micro-LED display applications. Finally, a tunable bio-inspired compound (BIC) eyes structure with a combination of dispensing and a dry-phase rubbing process is suggested as a hierarchical macro/micro-scale printed optical components. A hemispherical macrolens is formed by the dispensing method, followed by a dry-phase rubbing process for arranging micro particles in monolayer onto the curved surface of the macrolens. This hierarchical structure is replicated in soft materials, which have intrinsic stretchability. Microlens array is formed on the surface of the macrolens and acts as a rigid island, thereby maintaining lens shape, resolution, and focal length even though the mechanical strain is applied to overall hierarchical structures and the shape of the macrolens is changed. The primary purposes of this dissertation are to introduce new concepts of the enabling technologies for 3D printed optical components and to shed new light on them. Optical components can be easily made as 3D printing equipment becomes cheaper and more precise, so the field of Consumer optics or Do it yourself (DIY) optics will be gradually expanded on deformable and multi-scale optics. It is expected that this dissertation can contribute to providing a guideline for utilizing and customizing 3D printed optical components in next-generation display and imaging system applications.Chapter 1. Introduction 1 1.1. Manufacturing Process 1 1.2. Additive Manufacturing 4 1.3. Printed Optical Components 8 1.4. Motivation and Organization of Dissertation 11 Chapter 2. Macro-scale Printed Optical Components 15 2.1. Introduction 15 2.2. Seamless Modular Flat Display with Printed Lens 20 2.2.1. Main Concept 20 2.2.2. Experimental Section 23 2.2.3. Results and Discussion 26 2.3. Seamless Modular Curved-edge Display with Printed Mirror 32 2.3.1. Main Concept 32 2.3.2. Experimental Section 33 2.3.3. Results and Discussion 36 2.4. Conclusion 46 Chapter 3. Micro-scale Printed Optical Components 47 3.1. Introduction 47 3.2. Full-color Micro-LED Array with Printed Color-convertible Microlens 52 3.2.1. Main Concept 52 3.2.2. Experimental Section 54 3.2.3. Results and Discussion 57 3.3. Conclusion 65 Chapter 4. Hierarchical Macro/Micro-scale Printed Optical Components 66 4.1. Introduction 66 4.2. Tunable Bio-inspired Compound Eye with Printing and Dry-phase Rubbing Process 69 4.2.1. Main Concept 69 4.2.2. Experimental Section 71 4.2.3. Results and Discussion 73 4.3. Conclusion 79 Chapter 5. Conclusion 80 5.1. Summary 80 5.2. Limitations and Suggestions for Future Researches 83 References 88 Abstract in Korean (국문 초록) 107Docto

Eurodisplay 2019

The collection includes abstracts of reports selected by the program by the conference committee

High Performance Micro-scale Light Emitting Diode Display

Micro-scale light emitting diode (micro-LED) is a potentially disruptive display technology because of its outstanding features such as high dynamic range, good sunlight readability, long lifetime, low power consumption, and wide color gamut. To achieve full-color displays, three approaches are commonly used: 1) to assemble individual RGB micro-LED pixels from semiconductor wafers to the same driving backplane through pick-and-place approach, which is referred to as mass transfer process; 2) to utilize monochromatic blue micro-LED with a color conversion film to obtain a white source first, and then employ color filters to form RGB pixels, and 3) to use blue or ultraviolet (UV) micro-LEDs to pump pixelated quantum dots (QDs). This dissertation is devoted to investigating and improving optical performance of these three types of micro-LED displays from device design viewpoints. For RGB micro-LED display, angular color shift may become visually noticeable due to mismatched angular distributions between AlGaInP-based red micro-LED and InGaN-based blue/green counterparts. Based on our simulations and experiments, we find that the mismatched angular distributions are caused by sidewall emission from RGB micro-LEDs. To address this issue, we propose a device structure with top black matrix and taper angle in micro-LEDs, which greatly suppresses the color shift while keeping a reasonably high light extraction efficiency. These findings will shed new light to guide future micro-LED display designs. For white micro-LEDs, the color filters would absorb 2/3 of the outgoing light, which increases power consumption. In addition, color crosstalk would occur due to scattering of the color conversion layer. With funnel-tube array and reflective coating on its inner surface, the crosstalk is eliminated and the optical efficiency is enhanced by ~3X. For quantum dot-converted micro-LED display, its ambient contrast ratio degrades because the top QD converter can be excited by the ambient light. To solve this issue, we build a verified simulation model to quantitatively analyze the ambient reflection of quantum dot-converted micro-LED system and improve its ambient contrast ratio with a top color filter layer

Development of Position-Dependent Luminescent Sensors: Spectral Rulers and Chemical Sensing Through Tissue

Assessing the performance of medical devices is critical for understanding device function and monitoring pathologies. With the use of a smart device clinically relevant chemical and mechanical information regarding fracture healing may be deduced. For example, strain on the device may be used as a mechanical indicator of weight-bearing capacity. In addition, changes in chemical environment may indicate the development of implant associated infections. Although optical methods are widely used for ex vivostrain/motion analysis and for chemical analyses in cells and histological tissue sections, there utility is limited through thick tissue because light scattering reduces spatial resolution. This dissertation presents four novel luminescent sensors that overcome this limitation. The sensors are capable of detecting chemical and physical changes by measuring position or orientation-dependent color/wavelength changes through tissue. The first three sensors are spectral rulers comprised of two patterned thin films: an encoder strip and an analyzer mask. The encoder strip is either a thin film patterned with stripes of alternating luminescent materials (quantum dots, particles or dyes) or a film containing alternating stripes of a dye that absorbs luminescence from a particle film placed below. The analyzer mask is patterned with a series of alternating transparent windows and opaque stripes equal in width to the encoder lines. The analyzer is overlaid upon the encoder strip such that displacement of the encoder relative to the analyzer modulates the color/spectrum visible through the windows. Relative displacement of the sensor layers is mechanically confined to a single axis. When the substrates are overlaid in the “home position” one line spectrum is observed, and in the “end position,” another line spectrum is observed. At intermediate positions, spectra are a linear combination of the “home” and “end” spectra. The position-modulated signal is collected by a spectrometer and a spectral intensity ratio from closely spaced emission peaks is calculated. By collecting luminescent spectra, rather than imaging the device surface, the sensors eliminate the need to spatially resolve small features through tissue by measuring displacement as a function of color. We measured micron scale displacements through at least 6 mm of tissue using three types of spectral ruler based upon 1) fluorescence, 2) x-ray excited optical luminescence (XEOL), and 3) near infrared upconversion luminescence. The sensors may be used to investigate strain on orthopedic implants, study interfragmentary motion, or assess tendon/ligament tears. In addition to monitoring mechanical strain it is important to investigate clinically relevant implant pathologies such as infection. To address this application, we have developed a fourth type of sensor. The sensor monitors changes in local pH, an indicator of biofilm formation, and uses magnetic fields to modulate position and orientation-dependent luminescence. This modulation allows the sensor signal to be separated from background tissue autofluorescence for spectrochemical sensing. This final sensor variation contains a cylindrical magnet with a fluorescent pH indicating surface on one side and a mask on the other. When the pH indicating surface is oriented towards the collection optics, the spectrum generated contains both the sensor and autofluorescence signals. Conversely, when the pH sensor is oriented away, the collected signal is composed solely of background signals. All four of the sensors described can be used to build smart devices for monitoring pathologies through tissue. Future work will include the application of the strain and chemical sensors in vivo and ex vivo in animal and cadaveric models

Light trapping substrates and electrodes for flexible organic photovoltaics

Organic solar cells are one of the most promising candidates for future solar power generation. They are thin and lightweight with several additional advantages such as scalability, environmental sustainability and low cost for processing and installation. However, the low charge carrier mobility of the absorbing material for organic solar cells requires thin absorber layers, limiting photon harvesting and the overall power conversion efficiency. Several attempts, e.g., periodically patterned structures and scattering layers have been tried to enhance the absorption of thin-film solar cells as light trapping elements. However, much effort is required to introduce light trapping structures to conventional rigid metal oxide electrodes and glass substrate. For instance, almost 13 hours are required to fabricate micro structures of 1 m2 area on glass, in contrast, 1 minute on PET using a same laser set-up and an additional scattering layers are demanded for providing light trapping effects to solar cells. In the last years, flexibility is emerging as the one of the major advantages of organic solar cells. To realize flexibility of solar cells, the classically used glass substrates and ITO electrodes are too brittle. Therefore, polymer materials are promising candidates to replace them as flexible electrodes and substrates. In this thesis, the highly transparent conducting polymer, PEDOT:PSS and PET equipped with an AlOx encapsulation layer are used as electrode and substrate, respectively. Besides the flexibility, additional light trapping elements, e.g. scattering particles, nano- and microstructures can be easily applied to the polymer materials since they have the potential for easier shaping and processing. In this study, we apply different light trapping and in-coupling approaches to organic solar cells. First, PET substrates are structured with a direct laser interference patterning system, which is a powerful and scalable one-step technique for patterning polymers. Almost 80 % of the light is diffracted by these patterned PET substrates and thereby the light path in the absorption layer is increased. Optical display films, commercially developed to be used as back light units of liquid crystal displays are also examined as light trapping substrates and exhibit similar enhancement as patterned PET. Moreover, since PEDOT:PSS is prepared by a solution-based process, TiO2 nanoparticles are added as light scattering elements to the PEDOT:PSS electrodes. Consequently, those electrodes provide a dual function as electrical contact and light trapping element. Finally, 2- or 3-dimensional nanostructures are printed by a nano-imprinting technique onto the surface of PEDOT:PSS with PDMS stamps. By controlling the temperature and the time of PEDOT:PSS during an annealing step, nanostructures are transferred from PDMS masks to PEDOT:PSS. To evaluate the effects of light trapping for all above mentioned approaches, flexible organic solar cells are produced by vacuum evaporation using blends of DCV5T-Me and C60 as absorber layer. The substrates are optically characterized using UV-vis spectrometer and goniometer measurements. The topography of the samples is measured by atomic force microscopy, scanning microscopy and optical microscopy. Bending tests with various radii are performed to test the flexibility of the substrates. In summary, light trapping effects are successfully implemented in the electrodes and substrates for OPVs, giving efficiency improvements of up to 16 %. The light trapping mechanisms in our approaches are extensively discussed in this thesis.Organische Photovoltaik ist einer der vielversprechendsten Kandidaten für die zukünftige Solarstromgewinnung auf flexiblen Substraten. Um diese Flexibilität zu ermöglichen, sind herkömliche Glassubstrate mit ITO-Elektroden zu spröde. Ein vielversprechender Kandidat, um sowohl flexible Elektroden als auch flexible Substrate herzustellen, sind Polymere, da diese sehr biegsam und leicht zu verarbeiten sind. Deshalb wird in dieser Arbeit das hoch transparente, leitfähige Polymer PEDOT:PSS als Elektrode und PET (mit einer AlOx Verkapselungsschicht) als Substrat untersucht. Aufgrund der guten Prozessierbarkeit der Polymere konnten wir zusätzlich zu den eigentlichen Funktionen des Substrates und der Elektrode noch den Mechanismus des Lichteinfangs hinzufügen. Zusätzlich zu ihrer Flexibilität haben organische Solarzellen noch weitere Vorteile: sie sind dünn, leicht, skalierbar und verursachen vergleichsweise geringe Kosten für Herstellung und Installation. Ein Nachteil organischer Solarzellen ist die vergleichsweise geringe Ladungsträgerbeweglichkeit der Absorbermaterialien, welche oft die Schichtdicke der Absorbermaterialien begrenzt. Dies hat weniger absorbierte Photonen, weniger Stromdichte und somit einen geringeren Wirkungsgrad zur Folge. In den letzten Jahren wurden periodisch strukturierte Substrate und streuende Schichten als Lichteinfangelemente eingesetzt, um den Wirkungsgrad organischer Solarzellen mit dünnen Absorberschichten zu erhöhen. Gestaltungsregeln für solche Lichteinfangelemente sind noch weitestgehend unbekannt. Im Rahmen dieser Arbeit strukturieren wir PET Substrate mit einem direkten Laserinterferenzsystem, welches ein leistungsfähiges, skalierbares Einschrittverfahren zur Polymerstrukturierung ist. Da PEDOT:PSS aus der Lösung prozessiert wird, können wir weiterhin Nanopartikel hinzufügen, die der Elektrode zusätzlich noch lichtstreuende Eigenschaften geben. Außerdem können 2- bzw. 3-dimensionale Nanostrukturen leicht mithilfe einer Stempeltechnik eingeprägt werden. Um die Effekte des Lichteinfangs, welcher durch die oben genannten Methoden erzeugt wird, zu untersuchen, werden flexible organische Solarzellen mittels Vakuumverdampfung prozessiert. DCV5T-Me und C60 bilden dabei die photoaktive Schicht. Somit werden die Licht fangenden Eigenschaften dieser flexiblen Solarzellen ausgenutzt und ausführlich in der Arbeit diskutiert