Impact of Polymer Backbone Fluorination on the Charge Generation/Recombination Patterns and Vertical Phase Segregation in Bulk Heterojunction Organic Solar Cells

摘要： Incorporating fluorine (–F) substituents along the main-chains of polymer donors and acceptors is an effective strategy toward efficient bulk-heterojunction (BHJ) solar cells. Specifically, F-substituted polymers often exhibit planar conformations, leading to favorable packing, and electronic coupling. However, the effects of fluorine substituents on the charge generation and recombination characteristics that determine the overall efficiency of BHJ active layers remain critically important issues to examine. In this report, two PBDT[2X]T polymer analogs –poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-thiophene] [PBDT[2H]T] and its F-substituted counterpart poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-3,4-difluoro-thiophene] [PBDT[2F]T]—are studied to systematically examine how –F substituents impact the blend morphology, charge generation, carrier recombination and extraction in BHJ solar cells. Considering the large efficiency differences between PBDT[2H]T- and PBDT[2F]T-based BHJ devices, significant emphasis is given to characterizing the out-of-plane morphology of the blend films as vertical phase-separation characteristics are known to have dramatic effects on charge transport and carrier extraction in polymer-fullerene BHJ solar cells. Herein, we use electron energy loss spectroscopy (EELS) in tandem with charge transport characterization to examine PBDT[2X]T-fullerene blend films. Our analyses show that PBDT[2H]T and PBDT[2F]T possess very different charge generation, recombination and extraction characteristics, resulting from distinct aggregation, and phase-distribution within the BHJ blend films.

Corrigendum: Impact of Polymer Backbone Fluorination on the Charge Generation/Recombination Patterns and Vertical Phase Segregation in Bulk Heterojunction Organic Solar Cells

Backbone Fluorination of Polythiophenes Improves Device Performance of Non-Fullerene Polymer Solar Cells

摘要： Polythiophenes (PTs) are promising donor materials for the industrialization of polymer solar cells (PSCs) due to the merits of easy synthesis, low cost, and large-scale producibility. The rapid progress of non-fullerene acceptors requires the development of new PTs for use in non-fullerene PSCs. In this work, we present a set of PTs with different degree of backbone fluorination (P6T-F00, P6T-F50, P6T-F75, and P6T-F100) to investigate the effect of fluorination on the photovoltaic properties of PTs in non-fullerene PSCs. Upon increasing fluorine content, the PTs tend to have higher crystallinity, higher absorption coefficients, and enhanced relative dielectric constants. When blended with a non-fullerene acceptor EH-IDTBR, the blend films show increased photoluminescence quenching efficiency, reduced charge recombination loss, and extended charge carrier lifetime along with increasing fluorine content of PTs. These positive factors collectively result in dramatically improved power conversion efficiency from 4.3% for P6T-F00:EH-IDTBR to 7.3% for P6T-F100:EH-IDTBR, which is superior to the champion binary non-fullerene PSCs based on P3HT. Our results demonstrate that PTs are promising donor materials for non-fullerene PSCs via backbone fluorination.