Altering the Positions of Chlorine and Bromine Substitution on the End Group Enables High‐Performance Acceptor and Efficient Organic Solar Cells

Abstract

Molecular design of organic semiconductors plays an important role in development of organic solar cell (OSC) materials and devices. [1-6] It is generally believed that subtle structural changes could lead to significant variations in the optoelectronic properties and photovoltaic performance of organic semiconductors. In particular, many of such examples have been demonstrated in the area of nonfullerene small-molecule acceptors (SMAs), [7-16] which has been a major revolution of the OSC field in the past few years. Thanks to their easily modified chemical structures, the electrochemical, optoelectronic, and physical properties of the molecules can be tuned and optimized to achieve efficient donor and acceptor materials. [17-26] To date, the OSCs based on nonfullerene SMAs and polymer donors have demonstrated efficiencies of over 17%. [27-39] It is widely recognized that subtle changes in the chemical structure of organic semiconductors can induce dramatic variations in their optoelectronic properties and device performance, especially for the nonfullerene small-molecule acceptors (SMAs). For instance, halogenation of the end groups in the acceptordonor-acceptor-type SMAs is an effective strategy to modulate the properties of the end group and thus the entire SMA. While previous position modulations have focused on only one substituent, this study shows the development of three isomeric SMAs (BTP-ClBr, BTP-ClBr1, and BTP-ClBr2) via manipulating the position of two halogen substituents (chlorine and bromine) on the terminal unit. BTP-ClBr exhibits a blueshifted absorption, a shallower lowest unoccupied molecular orbital energy level, and a weaker crystallization tendency relative to BTP-ClBr1 and BTP-ClBr2. A power conversion efficiency (16.82%) and an excellent fill factor (FF) (0.79) are realized in the optimal PM6:BTP-ClBr organic solar cell device. The higher FF is consistent with the results of the characterization including a longer charge recombination lifetime, a faster photocurrent decay, a weaker bimolecular recombination, and a more favorable domain size for PM6:BTP-ClBr, which all originate from a subtle change in the substitution sites that strongly influences the physicochemical properties of the SMA.

Ternary Organic Photovoltaic Cells Exhibiting 17.59% Efficiency with Two Compatible Y6 Derivations as Acceptor

“…The obvious (010) diffraction peak at 1.77 Å −1 in OOP indirection and (100) diffraction peak at 0.28 Å −1 in IP direction can be observed from the 2D‐GIWAXS patterns of PM6:BTP‐BO‐4F blend films, suggesting the efficient charge transport along the normal direction of substrate due to the preferential face‐on orientation molecular arrangement of PM6 and BTP‐BO‐4F. [ 49–52 ] The preferential face‐on orientation molecular arrange of PM6 and BTP‐BO‐4F can be further confirmed from the occurrence of IP (200) diffraction in blend films in comparison with the neat films. The diffraction intensity of OOP (010) and IP (100) peaks in PM6:Y6‐1O blend films is slightly stronger than that in PM6:BTP‐BO‐4F blend films, indicating the more ordered molecular arrangement in PM6:Y6‐1O blend films.…”

Regio‐Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All‐Polymer Solar Cells with 15.2 % Efficiency

“…Therefore,w ei ntuitively design synthetic routes that can yield only one regiospecific product of dihalogenated terminal groups.T he synthetic routes to IC-FBr-o and IC-FBr-m are illustrated in Scheme 1. [50,51] By introducing the fluorine atom adjacent to one of the carbonyl groups of the precursor, the following condensation reaction will only occur at the other carbonyl group with less steric hindrance,r esulting in configuration-unique terminal group moieties and the corresponding SMA comonomers (Y-OD-FBr-o and Y-OD-FBrm). Notably,t he synthetic routes of these two regiospecific terminal groups are even easier and more efficient compared to that of the previous IC-FBr containing regio-isomers.…”

Side‐Chain Engineering on Y‐Series Acceptors with Chlorinated End Groups Enables High‐Performance Organic Solar Cells

“…[30][31][32] All the three parts can be reasonably designed and regulated to fine-tune the molecular properties of Y-series acceptors. [33][34][35][36][37][38][39][40][41] For example, if the chlorine atoms are used to replace the fluorine atoms in one of the famous Y-series acceptors named Y6, [42] the resulting molecule BTP-4Cl not only exhibits red-shifted absorption but also reduced voltage loss, leading to the BTP-4Cl-based devices showing an increased power conversion efficiency (PCE) of 16.5% with enhanced open-circuit voltage (V OC ) and short-circuit current density (J SC ) compared to those of the Y6-based devices. [43] It is also promising to modify the inner branched side chains which determine the solubility and crystallinity of Y-series acceptors.…”