검색 상세

Elucidation of operation and degradation mechanisms of efficient organic solar cells

  • 유신영 (아주대학교 일반대학원)

초록/요약

In this paper, we fabricated an inverted type of organic solar cell based on a non-fullerene acceptor (Y6). We measured the light intensity dependent JV characteristics of the devices and analyzed them using a computational simulation method. JV characteristic curves measured at various illuminances were able to be reproduced through the computational simulation with appropriate parameters. Through this, we confirmed that the light intensity dependence of the performance parameters of organic solar cells is closely related to the light intensity dependence of the bimolecular recombination and the SRH recombination, which are components of the recombination current. And we also confirmed that the device's performance is closely related to the dominant competition between the recombination current components. On the other hand, the interpretation of the JV characteristic curve through computational simulation is too complicated. And the interpretation through the 'Shockley' equation, which can be substituted for the simulation, does not explain the light intensity dependence of the recombination current. We were able to derive simple approximate forms describing the light intensity dependence of the recombination current by solving the transport equation and the Poisson equation with simple assumptions. And using this, we found a way to confirm the dominant recombination mechanism from the light intensity dependence of JV characteristics. We investigated the performance degradation of organic solar cells over time through the abovementioned method and the simulation. As a result, we confirmed that the oxidation of the ZnO layer caused the performance degradation of the device. And we could know that the resistance of other parts of the device except for the active layer could affect the recombination current and thus the device's performance

more

목차

Chapter 1 Introduction 1
1.1. Overview of organic solar cells 1
1.1.1. Development and Current Status of Organic Solar Cells 1
1.1.2. Performance and loss mechanisms of organic solar cells 2
1.2. Power loss due to the recombination current of organic solar cell 3
1.2.1. geminate recombination 3
1.2.2. non-geminate recombination 4
1.3. Light intensity dependent measurement and the interpretation 5
1.3.1. Light intensity dependent JV characteristics 5
1.3.2. Light-intensity-dependent JV characteristic analysis using computational simulation 6
1.4. Outline of the thesis 8
Chapter 2 Experiments 13
2.1. Device Fabrication 13
2.1.1. Fabrication of inverse type organic solar cell 13
2.1.2. Encapsulation process 14
2.2. Device structure, measurement/evaluation of the characteristics of the fabricated devices 15
2.2.1. JV characteristics and IPCE (Incident Photon-to-Current Efficiency) measurement 15
2.2.2. Measurement of the thickness and optical properties of each layer of the device 15
2.3. Computational Simulation 16
2.3.1. Optical simulation 16
2.3.2. Electrical simulation 17
Chapter 3 Light intensity dependence of JV characteristics and predominance switching between Shockley-Read Hall and bimolecular recombination losses 21
3.1. Introduction 21
3.2. Experimental results and discussion 22
3.2.1. Change of JV characteristic curve over time 22
3.2.2. Optical simulation 27
3.2.3. electrical simulation 28
3.2.4. Separation of recombination current components and analysis of JV characteristics through them 31
3.3. conclusion 39
Chapter 4 Limitations of the 'Shockley' model and the light intensity dependence of the recombination current 45
4.1. Introduction 45
4.2. Analysis of JV characteristics using 'Shockley model' 48
4.2.1. Overview of the 'Shockley model' 48
4.2.2. parasitic effect 50
4.2.3. The 'Shockley model' at the solar cell and the limitations 51
4.2.3.1. Dark condition 51
4.2.3.2. illumination condition 53
4.3. Solving transport equation 55
4.3.1. Definitions and anonyms 55
4.3.2. Basic assumptions and the simplest form of the transport equation 56
4.3.3. homogeneous solution 58
4.3.4. constant 'g' model 58
4.3.5. exponential 'g' model 59
4.3.6. Iteration method, considering the effect of U(x) 60
4.4. Approximate solution of Poisson equation and correction of the solution of transport equation reflecting it 63
4.4.1. Approximate solution of Poisson equation 65
4.4.2. Relation between Vf and Vint and correction of Ec0, Evf1 66
4.4.3. The correction of the approximation for charge carrier density 68
4.5. 'Jrec' approximation 70
4.6. conclusion 77
4.7. Detailed derivation 80
4.7.1. Definitions and anonyms 80
4.7.2. Calculation of 'Shockley model' 81
4.7.2.1. Basic relations in 'Shockley model' 81
4.7.2.2. Jbi in 'Shockley model' 81
4.7.2.3. JSRH in 'Shockley model' 82
4.7.3. Solving transport equation 83
4.7.3.1. Basic relations before solving transport equation 83
4.7.3.2. Simplest form of transport equation 84
4.7.3.3. homogeneous solution 86
4.7.3.4. Const 'g' model 87
4.7.3.5. exponential 'g' model 88
4.7.4. Considering Poisson equation 90
4.7.4.1. Pre-definition 90
4.7.4.2. Solving Poisson equation nearby cathode/ETL 91
4.7.4.3. Solving Poisson equation nearby HTL/Anode 93
4.7.4.4. Vf correction as a function of Vint 96
4.7.5. Approximation of Jrec 97
4.7.5.1. pre-definition 97
4.7.5.2. Jbi approximation in const 'g' mode 98
4.7.5.3. JSRH approximation in const 'g' model 100
4.7.5.4. 'knee' point in const 'g' model 103
Chapter 5 Analysis of the performance degradation over time in OSCs 104
5.1. Introduction 104
5.2. results and discussion 106
5.2.1. Change of JV characteristic curve over time 106
5.2.2. Variations over time of performance parameters and photoelectric conversion efficiency 108
5.2.3. The predominance of the recombination mechanism estimated by the light intensity dependence of Jrec/Jgen 109
5.3. Analysis of the JV characteristics and estimation of degradation mechanism through simulation 112
5.3.1. oxidation of ZnO layer and the effect of increment/decrement of oxygen vacancies 114
5.3.2. Computational simulation results and their interpretation 116
5.3.3. Correlation between the characteristic change of ZnO layer and JV characteristic curve 123
5.4. conclusion 131
Chapter 6 Conclusion 134
Publication list 139

more
반출 Meta View 목록