Pronounced Dependence of All‐Polymer Solar Cells Photovoltaic Performance on the Alkyl Substituent Patterns in Large Bandgap Polymer Donors. Issue 9 (1st April 2020)

• Record Type: Journal Article
• Authors: Chen, Jiale; Huang, Xuelong; Cao, Zhixiong; Liu, Shengjian; Liang, Kexin; Liu, Jinhai; Jiao, Xuechen; Zhao, Jiaji; Li, Qingduan; Cai, Yue‐Peng
• Is Part Of: Chemphyschem. Volume 21:Issue 9(2020)
• Page Start: 908
• Page End: 915
• Publication Date: 2020-04-01
• Subjects: alkyl substituent -- bandgap -- bulk-heterojunction -- polymer donor side chain -- polymer solar cells; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202000176
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: For all‐polymer solar cells which are composed of polymer donors and polymer acceptors, the effect of alkyl side chains on photovoltaic performance is a matter of some debate, and this effect remains difficult to forecast. In this concise contribution, we demonstrate that three alkyls namely branched alkyl 2‐butyloctyl (2BO), long linear alkyl n‐dodecyl (C12), and double‐short linear alkyl n‐hexyls (DC6) incorporated into the side chains of large bandgap polymer donor PBDT‐TTz can induce considerable, of significance, and different electronic, optical, and morphological parameters. Systematic studies shed light on the critical role of the double‐short linear alkyl n‐hexyls (DC6) in (i) producing large ionization potential value, (ii) increasing propensity of the polymer to order along the π‐stacking direction, (iii) generating polymer crystallites with more preferential "face‐on" orientation, consequently, (iv) improvement of carriers transportation, (v) suppression of charge recombination, (vi) reduction of energy loss in all‐polymer devices. In parallel, we unearth that the PBDT‐TTz with double‐short linear alkyl n‐hexyls (DC6) represents the highest efficiency of 8.3 %, whereas, the other two PBDT‐TTz analogues (2BO, C12) yield efficiencies of less than 3 % in optimized all‐polymer solar cells. Though branched or long linear alkyl side chains (2BO, C12) have been applied to provide the solution processability of conjugated polymers, motifs bearing multiple short linear alkyl substituents (DC6) are proved critical to the development of high performing polymers. Abstract : The importance of tailoring alkyl side chains to design high‐performing polymers is emphasized. Polymers with double‐n‐hexyls (DC6) present the largest ionization potentials and form highly ordered and strong face‐on backbone stackings that are desirable for achieving a higher open‐circuit voltage and an enhanced charge transportation, thus leading to the best efficiency of >8 %. On the contrary, polymers with bulky or long side chains perform worse in solar cells.