1 Supporting Information Efficiency Enhancements in Non-Fullerene Acceptor-Based Organic Solar Cells by Post-Additive Soaking Hoyeon Choi a† , Jihoon Lee b† , Chang-mok Oh a , Soyeong Jang b , Hyojung Kim c , Munseok Jeong c , Sung Heum Park b *, and In-Wook Hwang a * a Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea b Department of Physics, Pukyong National University, Busan 48513, Republic of Korea c Department of Energy Science, Sungkyunkwan University, Suwon 16419, Republic of Korea † These authors contributed equally to this work AUTHOR INFORMATION Corresponding Authors *Emails: hwangiw@gist.ac.kr (I.-W. Hwang); spark@pknu.ac.kr (S.H. Park) Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2019