Achieving Balanced Charge Transport and Favorable Blend Morphology in Non-Fullerene Solar Cells via Acceptor End Group Modification

Abstract

Generally, the electron-withdrawing substitution on the end-capping group of the acceptor−donor−acceptor type small-molecule acceptor (SMA) narrows the optical bandgap, and the electron-donating group lifts the lowest unoccupied molecular orbital (LUMO) energy level of nonfullerene SMA, which increase the short-circuit current density (J SC ) and open circuit voltage (V OC ) of the organic solar cells (OSCs), respectively; however, their synergistic effect on the properties of SMA has remained elusive. Here, we first report a new end-capping group (EG), namely, 5-fluoro-6-methyl-3-dicycanovinylindan-1-one (CFDCI), that concurrently possesses an electron-withdrawing fluorine substitute and an electron-donating methyl group. A prototype SMA (namely, ITCF) based on CFDCI and its two control counterparts were prepared to fully understand the structure− property relationship that the new EG exerts on the resultant SMA. The ITCF demonstrated a moderately crystalline morphology in pristine film and more balanced charge transport properties as well as a reduced amount of bimolecular recombination in blend film in comparison with its counterparts. The ITCF-based devices demonstrated a high power conversion efficiency (PCE) of 13.25% with an outstanding fill factor (FF) of 78.8%, which significantly outperformed their counterparts. Our study provides an important strategy to judiciously tune the properties of the SMAs for improving the performance of the OSCs.

Boron(iii) β-diketonate-based small molecules for functional non-fullerene polymer solar cells and organic resistive memory devices

“…Comparing the J61:1 and J61:2 blend lms, the larger RMS of the J61:1 blend lm reveals the presence of a pronounced phase separation with enhanced domain purity, which is advantageous for charge transport. [66][67][68] These ndings are in good agreement with the higher J sc and FF in the corresponding OSC devices. Similar results are also observed for the OSC devices fabricated with the J61:4 blend when compared to those fabricated with the J61:3 blend.…”

Thick‐Film Organic Solar Cells Achieving over 11% Efficiency and Nearly 70% Fill Factor at Thickness over 400 nm

“…Therefore, rationale design of thickness‐insensitive materials can be achieved from these three aspects, aiming at enhancing charge carrier mobilities and fine‐tuning the morphology. Functional groups such as methyl and fluorine with different degrees of electronegativity have been proven to be effective substituents on end groups, which play multiple roles in enhancing photovoltaic performance . Generally, gradually increase the number of methyl groups onto the end group will promote the charge carrier mobilities but can bring disadvantages to the morphology, while mono‐methylated end group gives better performance than its bis‐methylated derivative .…”

Recent Progress in Molecular Design of Fused Ring Electron Acceptors for Organic Solar Cells

“…In early 2019, Yang and co‐workers introduced both electron‐donating methyl group and electron‐withdrawing F atom in the DCI moiety to get novel end‐capping moiety CFDCI and synthesized a new FREA ITCF . As expected LUMO level was estimated to have value in between IT‐DM and IT‐4F .…”