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Developing Halogen‐Free Polymer Donors for Efficient Nonfullerene Organic Solar Cells by Addition of Highly Electron‐Deficient Diketopyrrolopyrrole Unit
Author(s) -
Ji Jingjing,
Xie Jiaqi,
Tang Junhui,
Zheng Kaibo,
Liang Ziqi
Publication year - 2021
Publication title -
solar rrl
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.544
H-Index - 37
ISSN - 2367-198X
DOI - 10.1002/solr.202100142
Subject(s) - moiety , energy conversion efficiency , materials science , conjugated system , copolymer , polymer , absorption (acoustics) , organic solar cell , homo/lumo , electron mobility , photochemistry , polymer chemistry , chemistry , optoelectronics , organic chemistry , molecule , composite material
High‐performance polymer donors when paired with nonfullerene acceptors are mainly limited to flanking halogenated benzodithiophene (BDT)‐based π ‐conjugated copolymers, which however involve complex synthetic procedures. Herein, a series of halogen‐free polymer donors that link BDT moiety with two highly electron‐deficient benzodithiophene‐dione (BDD) and diketopyrrolopyrrole (DPP) units with various molar ratios is developed. Compared with the benchmark PBDB‐T donor containing BDD unit, additional incorporation of a stronger electron‐negative DPP unit markedly lowers frontier molecular orbital levels and extends optical absorption, potentially leading to simultaneously enhanced V OC and J SC in organic solar cells. A remarkable power conversion efficiency (PCE) of 10.28% is thus obtained in the optimal P75 (BDD : DPP = 3:1 mol%) and Y6 blend cells in comparison with the reference PBDB‐T:Y6 (9.20%). A slight addition of PC 71 BM into the blend is found to further generate finer phase‐separated domains and thus increase the best efficiency up to 12.20%. The subtly critical roles of PC 71 BM are determined by transient absorption measurements on both thin‐film and in situ devices to be the prolonged free charge carrier lifetime and the shallow charge transfer states, which enhance J SC and fill factor in the device, respectively.