Perovskite light emitting diodes (PeLEDs) have recently broken the 20% barrier for external quantum efficiency (EQE). These high efficiencies are difficult to explain by assuming traditional models for optical outcoupling. We analyse the role of photon recycling (PR) in assisting light outcoupling in PeLEDs. Spatially resolved photoluminescence and electroluminescence analysis reveals the lateral spread of emission through recycling of photons trapped in substrate mode. While an outcoupling efficiency of 100% is theoretically possible with PR, parasitic absorption loss is shown to limit practical PR effects. Our optical modelling reveals that PR can contribute between 10 and 80% of the measured EQEs, depending on the optical structure of the PeLED. We demonstrate how the optical structure can be engineered in order to control the light emission. For example, a V-groove textured compound parabolic trapper is shown to improve the emission of a PeLED by 91 % in the desired direction.
Education & Work Experience
Visiting Scholar, University of Cambridge (01/05/2018 – present) PI: Prof. Neil Greenham Cavendish Laboratory, Department of Physics Postdoctoral Researcher, KAIST (01/03/2017 – present) PI: Prof. Jung-Yong Lee Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST) Graduate School of EEWS (Energy, Environment, Water and Sustainability), KAIST
 Changsoon Cho, Kibok Nam, Yeong Hwan Seo, Kyoohyun Kim, YongKeun Park, Jong-In Han*, and JungYong Lee*, “Study of Optical Configurations for Multiple Enhancement of Microalgal Biomass Production,” Scientific Reports, 9, 1723 (2019)  Ji-Won Seo, Jong Hun Kim, Mincheol Kim, Seon-Mi Jin, Sang-Hoon Lee, Changsoon Cho, Eunji Lee, Seunghyup Yoo, Jeong Young Park, Jung-Yong Lee*, “Columnar-structured Low-concentration Donor molecules in Bulk Heterojunction Organic Solar Cells,” ACS Omega, 3, 929 (2018)  Sung Yoon Min, Changsoon Cho, Gi Woong Shim, Ick-Joon Park, Dae Yool Jung, Youngjun Woo, JungYong Lee, and Sung-Yool Choi*, “Two-dimensional sheet resistance model for polycrystalline graphene with overlapped grain boundaries,” FlatChem, 7, 19 (2018)  Changsoon Cho, Jung Hoon Song, Changjo Kim, Sohee Jeong*, and Jung-Yong Lee*, “Broadband light trapping strategies for quantum-dot photovoltaic cells (>10%) and their issues with the measurement of photovoltaic characteristics,” Scientific Reports, 7, 17393 (2017) Curriculum Vitae – Changsoon Cho  Sang Woo Kim, Joonhyeong Choi, Thi Thu Trang Bui, Changyeon Lee, Changsoon Cho, Kwangmin Na, Jihye Jung, Chang Eun Song, Biwu Ma, Jung-Yong Lee, Won Suk Shin* and Bumjoon J. Kim*, “Rationally Designed Donor-Acceptor Random Copolymers with Optimized Complementary Light Absorption for Highly Efficient All-Polymer Solar Cells,” Advanced Functional Materials 27, 1703070 (2017)  Wonho Lee, Seonju Jeong, Changyeon Lee, Gibok Han, Changsoon Cho, Jung‐Yong Lee*, and Bumjoon J. Kim*, “Self‐Organization of Polymer Additive, Poly(2‐vinylpyridine) via One‐Step Solution Processing to Enhance the Efficiency and Stability of Polymer Solar Cells,” Advanced Energy Materials, 1602812 (2017)  Hyo Sang Lee†, Hyeng Gun Song†, Hyeseung Jung, Myung Hwa Kim, Changsoon Cho, Jung-Yong Lee, Sungnam Park, Hae Jung Son, Hui-Jun Yun, Soon-Ki Kwon, Yun-Hi Kim*, BongSoo Kim*, “Effects of Backbone Planarity and Tightly Packed Alkyl Chains in the Donor−Acceptor Polymers for High Photostability,” Macromolecules, 49, 7844 (2016)  Changsoon Cho†, Hyunbum Kang†, Se-Woong Baek, Taesu Kim, Changyeon Lee, Bumjoon Kim*, JungYong Lee*, “Improved Internal Quantum Efficiency and Light-Extraction Efficiency of Organic Light-Emitting Diodes via Synergistic Doping with Au and Ag Nanoparticles,” ACS Applied Materials & Interfaces, 8, 27911- 27919 (2016)  Seonju Jeong, Changsoon Cho, Jung-Yong Lee*, “Fabrication of Highly Efficient Organic Solar Cells via Incorporation of Various Periodic Metallic Nanogratings,” Polymer Science and Technology, 27, 206-211 (2016)  Changsoon Cho, Seonju Jeong and Jung-Yong Lee*, “Optical study of thin-film photovoltaic cells with apparent optical path length,” Journal of Optics, 18, 094001 (2016)  Juhoon Kang, Chang-Goo Park, Su-Han Lee, Changsoon Cho, Dae-Geun Choi and Jung-Yong Lee*, “Fabrication of high aspect ratio nanogrid transparent electrodes via capillary assembly of Ag nanoparticles,” Nanoscale, 8, 11217 (2016).  Jaeho Ahn†, Ji-Won Seo†, Jong Yun Kim, Jaemin Lee, Changsoon Cho, Juhoon Kang, Sung-Yool Choi, and Jung-Yong Lee*, “Self-Supplied Nano-Fusing and Transferring Metal Nanostructures via Surface Oxide Reduction,” ACS Appl. Mater. Interfaces, 8, 1112–1119 (2016).  Changsoon Cho, Seonju Jeong, Hwan-Jin Choi, Nara Shin, BongSoo Kim, Eun-chae Jeon, and Jung-Yong Lee* “Toward Perfect Light Trapping in Thin-Film Photovoltaic cells: Full Utilization of Dual Characteristics of Light”, Advanced Optical Materials, 3, 1697 (2015). (inside cover)  Juhoon Kang†, Changsoon Cho†, and Jung-Yong Lee*, “Design of asymmetrically textured structure for efficient light trapping in building integrated photovoltaics”, Organic electronics, 26, 61-65 (2015). – Citations: 2  Ali Canlier*, Umit Volkan Ucak, Hakan Usta, Changsoon Cho, Jung-Yong Lee, Unal Senc, Murat Citird, “Development of highly transparent Pd-coated Ag nanowire electrode for display and catalysis applications”, Applied Surface Science, 350, 79 (2015).  Seonju Jeong, Changsoon Cho, Hyunbum Kang, Ki-Hyun Kim, Youngji Yuk, Jeong Young Park, Bumjoon J. Kim*, and Jung-Yong Lee*, “Nanoimprinting-induced nanomorphological transition in polymer solar cells: enhanced electrical and optical performance”, ACS Nano, 9, 2773–2782 (2015).  Jeesoo Seok, Tae Joo Shin, Sungmin Park, Changsoon Cho, Jung-Yong Lee, Du Yeol Ryu, Myung Hwa Kim, and Kyungkon Kim*, “Efficient Organic Photovoltaics Utilizing Nanoscale Heterojunctions in Sequentially Deposited Polymer/fullerene Bilayer”, Scientific Reports, 5, 8373 (2015).  Myungkwan Song, Han-Jung Kim, Chang Su Kim, Jun-Ho Jeong, Changsoon Cho, Jung-Yong Lee, Sung-Ho Jin, Dae-Geun Choi* and Dong-Ho Kim*, “ITO-free highly bendable and efficient organic solar cells with Ag nanomesh/ZnO hybrid electrodes”, Journal of Materials Chemistry A, 3, 65-70 (2015).  Yeong Hwan Seo, Changsoon Cho, Jung-Yong Lee, Jong-In Han*, “Enhancement of growth and lipid production from microalgae using fluorescent paint under the solar radiation”, Bioresource Technology, 173, 193- 197 (2014).  Taegeon Kim†, Ali Canlier†, Changsoon Cho, Vepa Rozyyev, Jung-Yong Lee, Seung Min Han*, “Highly Transparent Au coated Ag Nanowire Transparent Electrode with Reduction in Haze”, ACS Applied Materials & Interfaces, 6, 13527-13534 (2014).  Se-Woong Baek, Garam Park, Jonghyeon Noh, Changsoon Cho, Chun-Ho Lee, Min-kyo Seo, Hyunjoon Song*, and Jung-Yong Lee*, “Au@Ag Core-Shell Nanocubes for Efficient Plasmonic Light Scattering Effect in Low Bandgap Organic Solar Cells”, ACS Nano, 8, 4, 3302-3312 (2014).  Cheng Jin An, Hae-Wook Yoo, Changsoon Cho, Jong-Min Park, Jong Kil Choi, Ming Liang Jin, Jung-Yong Lee and Hee-Tae Jung*, “Surface Plasmon Assisted High Performance Top-Illuminated Polymer Solar Cells with Nanostructured Ag Rear Electrodes “, Journal of Materials Chemistry A, 2, 2915-2921 (2014). – Citations: 15  Cheng Jin An, Changsoon Cho, Jong Kil Choi, Jong-Min Park, Ming Liang Jin, Jung-Yong Lee, Hee-Tae Jung*, “Highly Efficient Top‐Illuminated Flexible Polymer Solar Cells with a Nanopatterned 3-Dimensional Microresonant Cavity”, Small, 10, 7, 1278–1283 (2014).  Changsoon Cho†, Hoyeon Kim†, Seonju Jeong, Se-Woong Baek, Ji-Won Seo, Donggeon Han, Kyoohyun Kim, YongKeun Park, Seunghyup Yoo*, and Jung-Yong Lee*, “Random and V-groove texturing for efficient light Curriculum Vitae – Changsoon Cho trapping in organic photovoltaic cells,” Solar Energy Materials and Solar Cells, 115, 36-41 (2013). – Citations: 31  Changsoon Cho and Jung-Yong Lee*, “Multi-scale and angular analysis of ray-optical light trapping schemes in thin-film solar cells: Micro lens array, V-shaped configuration and double parabolic trapper,” Optics Express, 21, S2, A276–A284. (2013)  Dong Jin Kang, Hyunbum Kang, Changsoon Cho, Ki-Hyun Kim, Seonju Jeong, Jung-Yong Lee*, Bumjoon J. Kim*, “Efficient Light Trapping in Inverted Polymer Solar Cells by Randomly Nanostructured Electrode Using Monodispersed Polymer Nanoparticles,” Nanoscale, 5(5), 1858-63.(2013, back cover) 1.2. Conference Proceedings •H. J. Choi, E. c. Jeon, S. W. Woo, C. S. Cho, C. E. Kim, T. J. Je, J. Y. Lee, B. S. Shin, “Study on High-Aspect Ratio Parabolic Patterns Machining Using Planing,” Proceedings of KSPE 2014 Spring Conference, Jeju, Korea. •S YOO, D HAN, H KIM, C CHO, JY LEE, “Light management toward efficient organic solar cells,” Renewable Energy and the Environment (Optical Instrumentation for Energy and Environmental Applications), 2013, Tuscon, AZ., US. (DOI: 10.1364/E2.2013.ET3A.2) •Hyung-Man Lee, Chang-Soon Cho, Ju-Hoon Kang, Seok-Hwan Moon, Chang-Wan Byeon, Hun-Gwang Lim, Kun-Sik Ahn, and Jung-Yong Lee “Optical design and characterization of Fresnel lens for concentrated photovoltaic manufacturing,” ICMTE 2012, Seoul, Korea.
•“Shape-transformable compound parabolic solar concentrator,” Korea, Application No. 10-2018-0017666. •“Four-terminal Multi-junction Photovoltaic Cell using Optical Microstructure,” Korea, Application No. 10-2018- 0020990. •“Lossless Photovoltaic System using Patterned Array and Method of Manufacturing thereof,” Korea, Application No. 10-2017-0037907. 2.2. Patents (granted) •“HYBRID SOLAR ENERGY CONVERSION TECHNOLOGY FOR THE SIMULTANEOUS PRODUCTION OF ELECTRICITY AND BIOFUEL,” Korea, Grant No. 10-1761063 •“Organic thin-film photovoltaic cell using transparent texturing film,” Korea, Grant No. 10-1406882. •“Concentrator-integrated light trapping