Modelling various solar cells materials using lorentzian-drude coefficients

In order to develop an optoelectronic model for simulating different light trapping structures sandwiching the photovoltaic active layer, determining the materials dispersion and absorption properties is a must. The targeted model should be able to simulate the desperation and absorption capabilities of different conductor and semiconductor materials over the entire sun spectrum (200 nm to 1700 nm). Therefore, the Lorentzian-Dude (LD) model is chosen due to its simplicity in implementation with the finite difference time domain algorithm chosen for optical modelling. In this paper, various materials are selected to be modelled with the LD model. The proposed algorithm is not only used for modelling material behaviour of various conducting materials published in literature, but is also used for other conducting and semiconducting materials that the original model was not capable of modelling over the entire range of spectrum. Besides that, the suggested algorithm showed a better time performance than those mentioned in literature. Experimental 1D grating structure prototype samples were made to validate the simulation results, showing perfect agreement

FDTD modeling of solar energy absorption in silicon branched nanowires

Thin film nanostructured photovoltaic cells are increasing in efficiency and decreasing the cost of solar energy. FDTD modeling of branched nanowire ‘forests’ are shown to have improved optical absorption in the visible and near-IR spectra over nanowire arrays alone, with a factor of 5 enhancement available at 1000 nm. Alternate BNW tree configurations are presented, achieving a maximum absorption of over 95% at 500 nm

Effective optical response of silicon to sunlight in the finite-difference time-domain method

The frequency dependent dielectric permittivity of dispersive materials is commonly modeled as a rational polynomial based on multiple Debye, Drude, or Lorentz terms in the finite-difference time-domain (FDTD) method. We identify a simple effective model in which dielectric polarization depends both on the electric field and its first time derivative. This enables nearly exact FDTD simulation of light propagation and absorption in silicon in the spectral range of 300–1000 nm. Numerical precision of our model is demonstrated for Mie scattering from a silicon sphere and solar absorption in a silicon nanowire photonic crystal. © 2011 Optical Society of America OCIS codes: 000.3860, 000.4430, 350.6050. The finite-difference time-domain (FDTD) method [1] is widely used in computational electrodynamics for light scattering from arbitrary shaped objects [1], transmission and reflection at various incident angles for planar layers of scatterers [1,2], and photonic band structure of infinite periodic structures [3,4]. Unlike frequency domain methods, the dielectric permittivity ε ω of dispersive materials in tabular form canno

박막형 태양전지 수치해석을 위한 효율적 알고리즘에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 협동과정 계산과학 전공, 2013. 8. 신동우.본 논문에서는 무작위의 복잡한 3차원 표면 형상을 가진 물체를 평균적으로 O(logN) 시간 복잡도를 가지고 교차검사를 수행할 수 있는 새로운 알고리즘을 기반으로 박막형 태양전지 (Thin Film Solar Cell)의 흡수 효율을 효과적으로 시뮬레이션 하기 위한 방법을 논하였다. 3차원 피라미드 형상을 박막형 태양전지 표면에 양각한 경우, 3차원 표면 형상의 크기와 밀도가 흡수 효율에 영향을 미치게 되므로 이들에 대한 최적 설계 값들을 찾고자 시뮬레이션 방법을 이용한다. 본 연구에서는 무수히 많은 3차원 표면 형상들에 대한 최적의 교차검사 알고리즘을 kd-tree 가속화 구조를 변형하여 개발하였고, 이를 광선 추적 법 (Ray tracing)에 적용하여 평균 교차검사 시간을 O((log N)으로 하는 새로운 광선 추적에 의한 시뮬레이션 방법을 고안하였다. 이 방법은 기존 연구들에서 한번도 연구되지 않은 새로운 방법으로, 표면 형상들을 실제 객체로 인지하여 교차검사를 수행하면서도 종래의 O(N)~O(N2) 교차검사 시간을 O(log N)으로 단축시키는 결과를 얻었다. 또한 이전 연구들에서 반사율 시뮬레이션에 의존하여 간접적으로 계산하던 에너지 흡수 효율을 직접적으로 시뮬레이션 함은 물론이고 각 층별 에너지 흡수율을 간섭현상을 반영하여 직접적으로 시뮬레이션 할 수 있는 방법을 고안하였다. 이 알고리즘의 효율성 및 정확성은 다른 알고리즘과의 수행 시간 비교 및 실측 자료와 시뮬레이션 결과와의 오차 분석을 통해 검증 하였다. 박막형 태양전지의 크기가 나노미터 단위로 작아진 경우, 유한차분 시간영역 (FDTD)법을 이용하게 되는데, 현재까지 연구된 방법들로는 적은 전산 자원을 사용하여 빠른 시간 내에 정확한 흡수 에너지를 계산하는데 한계가 있었다. 본 연구에서는 이 문제를 해결하기 위하여 자유로운 형태의 시스템에 대해서 각 물질들의 연속된 경계 면을 효율적으로 추출하여 Poynting 이론의 발산 (Divergence) 부분의 식을 적용하는 방법으로 적은 전산 자원으로 빠른 시간 내에 상당한 정확도를 가지고 흡수 에너지를 계산할 수 있는 방법을 고안하였다. 이 방법의 정확성은 해석 가능한 모델의 Mie 확산 모델의 계산 결과와 시뮬레이션 결과를 비교함으로써 검증하였으며, 곡면 모델에 대해서는 곡률 반경을 변화시켜가며 시뮬레이션 한 결과가 물리적 유의성을 나타냄을 보임으로써 검증 하였다.In this thesis, I proposed a novel intersection algorithm based absorption en-ergy simulation methods for thin film solar cells which use a 3-D randomly textured geometry or plasma effects. For the case of pyramidal textured thin film solar cells, Optimizing the de-sign of the surface texture is an essential aspect of the thin film Si solar cells technology as it can maximize the light trapping efficiency of the cells. Thus, the appropriate simulation tools can provide efficient means of designing and analyzing the effects of the texture patterns on light confinement in an active medium. A ray tracing method is a powerful numerical simulation methodol-ogy for this. However, in past researches, a real object intersection method take an O(N2) time complexity and some height map method take an O(N) time complexity. These are time consuming process and inaccurate process, so I developed a novel intersection algorithm with an O(logN) time com-plexity and with keeping the accuracy. Also, an absorption energy calculation algorithm for each layer with a direct method did not exist in the past. To solve the intersection finding problem, I proposed a novel and an efficient 3-D texture intersection algorithm using a modified kd-tree traversal method in Chapter 2. Also, to solve the absorption efficiency calculation problem with ray tracing method, I proposed a new method in Chapter 3. The correctness and efficiency of the algorithms was validated by a measured data and numer-ical simulations. The thickness of the thin film solar cells reach to the nanometer size. The ray tracing method is useless for the nanometer size systems except for a flat surface type. In this case, the FDTD method can be used to solve this nanome-ter scale problems. However, by the past researches, an auto-discretization problem and an absorption efficiency calculation problem were not solved efficiently. In this research, I proposed a robust and an efficient auto-discretization algorithm and an efficient absorption energy calculation algo-rithm with a continuous boundary extraction algorithm in Chapter 4. The correctness and efficiency of the algorithms was validated by an exact solu-tion and numerical simulations. Through this thesis, I proposed an efficient absorption efficiency calcula-tion algorithms for all system ranges of the thin film solar cells.Abstract Publications Table of Contents List of Figures List of Tables List of Algorithms Symbols Abbreviations 1. Introduction 1.1 Motivation 1.2 Thin Film Solar cells 1.2.1 Reduction of Front Surface Reflectance 1.2.2 Enhancement of Back Surface Reflectance 1.2.3 Efficient Light Trapping 1.3 Ray Tracing 1.3.1 Finding Intersection 1.3.1.1 Primitive Object Case 1.3.1.2 CSG Object Case 1.3.2 Acceleration Scheme 1.4 Finite Difference Time Domain (FDTD) 1.4.1 Discretization of the System Domain 1.4.2 Dispersive Materials 1.4.2.1 Lorentz Model 1.4.2.2 Drude Model 1.4.2.3 Drude-Lorentz Model 1.4.3 Boundary Condition 1.4.3.1 Absorbing Boundary Condition (ABC) 1.4.3.2 Periodic Boundary Condition (PBC) 1.5 Scope and Objectives 1.6 Achievements 2. Slab-Outline Algorithm for Fast Intersection Finding 2.1 Overview 2.2 Algorithm 2.2.1 Non-overlapped texture case 2.2.2 Overlapped pyramidal texture case 2.3 Numerical Results : Validation 2.3.1 Examine of Backward Ray Tracing Results 2.3.2 Comparison of Experimental Results 2.3.3 Error Analysis 2.3.4 Time Complexity 2.4 Numerical Analysis : Applications 2.4.1 Simulation 2.4.2 Results and discussion 2.5 Conclusion 3. Simulation with Ray Tracing Method 3.1 Overview 3.2 Algorithm 3.3 Validation 3.3.1 Case I - coherent system 3.3.2 Case II - incoherent system 3.3.3 Case III - coherent + incoherent complex system 3.4 Numerical Analysis : Applications 3.4.1 High-efficiency Grid-type Si Solar Cell Structure 3.4.1.1 Overview 3.4.1.2 Simulation model 3.4.1.3 Results and Discussion 3.4.2 Effect of oxide thin films in back contact on the optical absorption efficiency of thin crystalline Si solar cells 3.4.2.1 Overview 3.4.2.2 Simulation model 3.4.2.3 Results and Discussion 3.5 Conclusion 4. Simulation with FDTD Method 4.1 Overview 4.2 Auto-Discretization of the System Domain 4.2.1 Algorithm 4.2.2 Results of Auto-Discretization 4.3 Implementation of Lorentz Model with ADE 4.4 EffectiveMaterial Function 4.4.1 Round-Off Algorithm 4.4.2 Dispersive Conformal FDTD (D-CFDTD) Algorithm 4.4.3 Validation 4.4.4 Numerical Analysis 4.5 Simulation of Absorption Energy 4.5.1 Algorithm 4.5.1.1 Extract Object's Continuous Boundary 4.5.1.2 Memory allocation and index mapping for the boundary cells 4.5.1.3 Calculation of the absorption energy 4.5.2 Numerical Analysis 4.5.2.1 Flat system 4.5.2.2 Non-Flat system 4.6 Conclusion 5. Conclusion 5.1 Summary 5.2 Evaluation 5.3 Future Work References Appendix I 국문초록 감사의 글Docto

Synthèse, caractérisation et modélisation de matériaux en couches minces pour l’optique en vue d’applications

Les travaux réalisés ces dernières années m’ont amené à combiner ces trois aspects : synthèse de matériaux, caractérisations et modélisation. A propos de la synthèse de matériau, j’ai utilisé la synthèse par voie chimique pendant ma thèse (film mince de PZT) et mon postdoc (film mince polymère). A Caen, les méthodes de synthèse utilisées sont des méthodes physiques comme la pulvérisation cathodique magnétron. Mes activités directes sont actuellement plus centrées sur la caractérisation et la modélisation des matériaux optiques, réalisés au sein de l’équipe NIMPH ou étudiés par l’intermédiaire de collaborations. Dans la suite du manuscrit, je vais détailler les travaux post-doctoraux expérimentaux et théoriques réalisés en Suède, à Caen et en collaboration avec des laboratoires partenaires. Certains sujets ayant fait l’objet de publications détaillées seront brièvement abordés d’autres sujets ayant fait l’objet de moins de publications seront plus densément développés