Realizing an Unprecedented Fill Factor of 82.2% in Ternary Organic Solar Cells via Co‐Crystallization of Non‐Fullerene Acceptors

Abstract

Ternary strategy is demonstrated as an efficient approach to achieve high short‐circuit current and open‐circuit voltage to boost the performance of organic solar cells (OSCs), however, the realization of high fill‐factor (FF) in ternary OSCs has been rare. In this study, three thiophene terminated non‐fullerene acceptors (NFAs) with methyl or chlorine substitutions on their end‐groups are designed and synthesized, and further incorporated into the state‐of‐the‐art PM6:L8‐BO system to construct ternary OSCs. Subtle changes in their chemical structures significantly modify the molecular packings of these thiophene terminated NFAs. While BTP‐ThMe and BTP‐ThCl have limited forms of dimer, versatile molecular dimers, including “Z” shaped D‐D, “S” shaped A‐A, and “F” shaped A‐D packings exist in BTP‐ThMeCl, which lead to the formation of compact 3D honey‐comb network and this is analogous to the host acceptor L8‐BO. This synergetic molecular packing between BTP‐ThMeCl and L8‐BO contributes to maintain the 3D charge transport network in the ternary system via the formation of NFA co‐crystals at the molecular level, and consequently realizing a maximum power conversion efficiency of 19.1% with a superior FF of 82.2%, which is the highest FF reported so far for OSCs.

Bicontinuous donor and acceptor fibril networks enable 19.2% efficiency pseudo‐bulk heterojunction organic solar cells

“…The improved fibril network is associated with enhanced (010) and (021) diffraction peaks of L8‐BO (Figure 4D–F and Supporting Information S1: Figure ), denoting the enhanced fibril morphology might be attributed to L8‐BO. [ 35 ] As such, these optimized fibril networks also translate to extended exciton lifetime and improved exciton diffusion (Figure 3D and Supporting Information S1: Table ) for both PM6 and L8‐BO, contribute to enhanced hole and electron mobilities (Supporting Information S1: Figure and Table 2), and finally result in improved exciton dissociation and charge collection efficiency (Figure 3E and Table 2) toward superior FF and J SC as we presented above.…”

“…While it is not challenging to realize fibrillation for neat organic components, this situation can be very complicated when binary or ternary components are mixed to construct photoactive layer for OSCs, as their self‐assembly can compete with each other. [ 32,33 ] Although very recent works have demonstrated that the fibrillization of polymer donors or NFAs in mixed films can be enhanced via the co‐crystallization of the conjugated polymers having high compatibility (i.e., D18‐Cl and PM6) [ 25,34 ] or NFAs with similar molecular packing forms (i.e., BTP‐ThMeCl and L8‐BO), [ 35 ] it is still difficult to construct fibrils of donor and acceptor components simultaneously to realize bicontinuous charge transport networks.…”

Hole‐Transporting Polymers Bearing Fine‐Tuning Side Chains via Ternary Copolymerization Strategy for High‐Performance Perovskite Solar Cells

“…Thus the obvious phase separation appears in their blend film. [33,40] As can be seen from the AFM height images with the scale of 1 μm × 1 μm (Figure S5a, Supporting Information), PT-Cz50 film exhibits finer nanoscale fibrillar texture with a slightly lower RMS roughness value of 1.31 nm compared with PA-Cz50, which contributes to the efficient hole transport. [41,42] Figure S5b (Supporting Information) confirms the distinct phase separation of PA-Cz50 again.…”

Alkoxythiophene‐Directed Fibrillization of Polymer Donor for Efficient Organic Solar Cells

“…[9][10][11] Throughout the history of OSCs, constructing bicontinuous heterojunction structure with fibrillar networks has been proved to be an effective strategy for obtaining superior OSCs, which allows sufficient interfaces between donor and acceptor for efficient exciton dissociation and continuous donor/acceptor domains for efficient carrier transport. [12][13][14][15][16][17][18][19][20][21][22] For example, we recently reported a fused-ring solid additive 1-fluoronaphthalene (FN) [12] that can improve the intermolecular main-chain interactions among nonfullerene acceptors (NFAs) and consequently promote the formation of nanofibrillar NFA for superior electron transport, with the fill factor of relevant device increased from 69.4% to 80%. Optimizing the molecular packing of organic semiconductors into ordered, fine, and fibrillar aggregation to promote light absorption, exciton dissociation, and charge transport has been identified as a crucial step to further enhance their photovoltaic performance.…”