Optimization and Analysis of Conjugated Polymer Side Chains for High‐Performance Organic Photovoltaic Cells |
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| Authors: | Ji‐Hoon Kim Sebastian Wood Jong Baek Park Jessica Wade Myungkwan Song Sung Cheol Yoon In Hwan Jung Ji‐Seon Kim Do‐Hoon Hwang |
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| Affiliation: | 1. Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan, Republic of Korea;2. Department of Physics and Centre for Plastic Electronics, Imperial College London, London, UK;3. Surface Technology Division Korea Institute of Materials Science, Changwon, Republic of Korea;4. Advanced Materials Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon, Republic of Korea |
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| Abstract: | Optimization and analysis of conjugated polymer side chains for high‐performance organic photovoltaic cells (OPVs) reveal a critical relationship between the chemical structure of the side chains and photovoltaic properties of polymer‐based bulk heterojunction OPVs. In particular, the impact of the alkyl side chain length on the π‐bridging (thienothiophene, TT) unit is considered by designing and synthesizing a series of benzodithiophene derivatives (BDT(T)) and thieno3,2‐b]thiophene‐π‐bridged thieno3,4‐c]pyrrole‐4,6(5H)‐dione (ttTPD) alternating copolymers, PBDT(T)‐(R2)ttTPD, with alkyl chains of varying length on the TT unit. Using a combination of 2D X‐ray diffraction, Raman spectroscopy, and electrical device characterization, it is elucidated in detail how these subtle changes to the chemical structure affect the molecular conformation, thin film molecular packing, blend film morphology, optoelectronic properties, and hence overall photovoltaic performance. For copolymers employing both the alkoxy or alkylthienyl‐substituted BDT motifs, it is found that octyl side chains on TT unit yield the maximum degree of molecular backbone coplanarity and result in the highest quality of molecular packing and optimized hole mobility. Inverted devices fabricated using this PBDTT‐8ttTPD: polymer/6,6]‐phenyl‐C71‐butylic acid methyl ester active layer show a maximum power conversion efficiency (PCE) of 8.7% with large area cells (0.64 cm2) maintaining a PCE of 7.5%. |
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| Keywords: | 2D‐GIXD BDT‐TPD‐based copolymers organic photovoltaic cells resonant Raman spectroscopy side chains |
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