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Optimization and Analysis of Conjugated Polymer Side Chains for High‐Performance Organic Photovoltaic Cells
Author(s) -
Kim JiHoon,
Wood Sebastian,
Park Jong Baek,
Wade Jessica,
Song Myungkwan,
Yoon Sung Cheol,
Jung In Hwan,
Kim JiSeon,
Hwang DoHoon
Publication year - 2016
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201504093
Subject(s) - materials science , side chain , conjugated system , thiophene , polymer , polymer solar cell , alkyl , alkoxy group , raman spectroscopy , energy conversion efficiency , active layer , polymer chemistry , chemical engineering , organic chemistry , optoelectronics , layer (electronics) , nanotechnology , thin film transistor , chemistry , composite material , optics , physics , engineering
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 thieno[3,2‐b]thiophene‐π‐bridged thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (ttTPD) alternating copolymers, PBDT(T)‐(R 2 )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‐C 71 ‐butylic acid methyl ester active layer show a maximum power conversion efficiency (PCE) of 8.7% with large area cells (0.64 cm 2 ) maintaining a PCE of 7.5%.