A Non-fullerene Acceptor with Enhanced Intermolecular π-Core Interaction for High-Performance Organic Solar Cells

Abstract

Understanding the molecular structure and self-assembly of thia­diazole-derived non-fullerene acceptors (NFAs) is very critical for elucidating the origin of their extraordinary charge generation and transport properties that enable high power conversion efficiencies to be achieved in these systems. A comprehensive crystallographic study on a state-of-the-art NFA, Y6, and its selenium analog, CH1007, has been conducted which revealed that the face-to-face π-core interaction induced by benzo­[2,1,3]­thia­diazole S–N-containing moieties plays a significant role in governing the molecular geometries and unique packing of Y6 and CH1007 to ensure their superior charge-transport properties. Moreover, benefitting from the red-shifted optical absorption via selenium substitution, photo­voltaic devices based on a PM6:CH1007:PC71BM ternary blend delivered an exceptionally high short-circuit current of 27.48 mA/cm2 and a power conversion efficiency of 17.08%.

Asymmetric Acceptors Enabling Organic Solar Cells to Achieve an over 17% Efficiency: Conformation Effects on Regulating Molecular Properties and Suppressing Nonradiative Energy Loss

“…[ 45–47 ] Most importantly, Y6's banana shape allows it to stack closely to form a 3D framework with effective charge transfer/transport channels (bipolar transport property). [ 45–51 ] Consequently, the blend of Y6 with PM6 achieved an unprecedented PCE (15.7%) with a 0.50 eV E loss in binary devices. [ 6 ]…”

“…[44] In addition, its dipyrrolobenzo[c] [1,2,5] thiadiazole (BP) moiety within the fused core strengthens the intermolecular π-π stackings through S-N (on thiadiazole unit) noncovalent interactions and reduces the E loss . [45][46][47] Most importantly, Y6's banana shape allows it to stack closely to form a 3D framework with effective charge transfer/transport channels (bipolar transport property). [45][46][47][48][49][50][51] Consequently, the blend of Y6 with PM6 achieved an unprecedented PCE (15.7%) with a 0.50 eV E loss in binary devices.…”

“…[45][46][47] Most importantly, Y6's banana shape allows it to stack closely to form a 3D framework with effective charge transfer/transport channels (bipolar transport property). [45][46][47][48][49][50][51] Consequently, the blend of Y6 with PM6 achieved an unprecedented PCE (15.7%) with a 0.50 eV E loss in binary devices. [6] Limited by the unique packing features and synthetic difficulty of Cadogan reaction, the main optimizations performed currently for Y6 were focused on its side chains and terminal groups hoping to fine-tune the NFA's crystalline properties.…”

“…Noticeably, NFA with high V oc in device is desirable because it can be applied to a ternary blend to compensate large V oc loss for materials with high J sc , however, such type of acceptors is relatively scarce especially in the Y6 system. [57,58] Benefited from the high V oc of BP5T-4F and high J sc of CH1007, [45] ternary OSCs based on PM6:BP5T-4F:CH1007 (1:1.02:0.18) were fabricated to enhance the PCE to 17.2%. These results showed that asymmetric cores can induce significant conformation effects on Y6-type NFAs, and the resulting Z-shape and W-shape conformation NFAs can reduce E loss .…”

“…[57][58] In this regard, our finding provides a new molecular design strategy for achieving highperformance NFAs with high V oc . CH1007 is a high-performance NFA recently reported by our group (Figure S7, Supporting Information) [45] which contains two selenophenes at the end of the π-core to enable stronger intermolecular interaction and a reduced bandgap. As a result, OSCs based on PM6:CH1007 showed a high PCE of 15.96% along with a V oc of 0.820 V, a J sc of 27.03 mA cm −2 , and an FF of 72%.…”