Suppressing Kinetic Aggregation of Non‐Fullerene Acceptor via Versatile Alloy States Enables High‐Efficiency and Stable Ternary Polymer Solar Cells

Abstract

Despite considerable advances devoted to improving the operational stability of organic solar cells (OSCs), the metastable morphology degradation remains a challenging obstacle for their practical application. Herein, the stabilizing function of the alloy states in the photoactive layer from the perspective of controlling the aggregation characteristics of non‐fullerene acceptors (NFAs), is revealed. The alloy‐like model is adopted separately into host donor and acceptor materials of the state‐of‐the‐art binary PM6:BTP‐4Cl blend with the self‐stable polymer acceptor PDI‐2T and small molecule donor DRCN5T as the third components, delivering the simultaneously enhanced photovoltaic efficiency and storage stability. In such ternary systems, two separate arguments can rationalize their operating principles: (1) the acceptor alloys strengthen the conformational rigidity of BTP‐4Cl molecules to restrain the intramolecular vibrations for rapid relaxation of high‐energy excited states to stabilize BTP‐4Cl acceptor. (2) The donor alloys optimize the fibril network microstructure of PM6 polymer to restrict the kinetic diffusion and aggregation of BTP‐4Cl molecules. According to the superior morphological stability, non‐radiative defect trapping coefficients can be drastically reduced without forming the long‐lived, trapped charge species in ternary blends. The results highlight the novel protective mechanisms of engineering the alloy‐like composites for reinforcing the long‐term stability of NFA‐based ternary OSCs.

Unraveling the Mystery of Ternary Organic Solar Cells: A Review on the Influence of Third Component on Structure–Morphology–Performance Relationships

“…Many studies have shown that the addition of a third component can circumvent this issue, leading to more optimal sized domains and improved morphological stability. [ 97,108,119–121 ]…”

“…More importantly, the ternary configuration showed relatively higher PCE compared with the binary counterparts as annealing temperature increases, signifying the morphological stability imposed by the homogenous acceptor phase in preventing PCE loss. In Zhang's work, [ 119 ] a PM6:BTP‐4Cl system was studied. PM6:BTP‐4Cl suffers from the performance‐degrading aggregation of the BTP‐4Cl acceptor.…”

Triplet‐Charge Annihilation in a Small Molecule Donor: Acceptor Blend as a Major Loss Mechanism in Organic Photovoltaics

“…[34,35] Also, DRCN5T has shown efficiencies close to 11% when blended with NFAs [36] and is widely used as a material in ternary blends given its near infrared absorption, recently obtaining almost 17% solar cell efficiency. [31,[37][38][39][40] In addition, DRCN5T has attracted special attention given its stability versus oxygen, especially after thermal annealing. [41,42] It is also able to increase PC70BM air and light stability, showing negligible short-circuit current loss.…”

Realizing Stable High‐Performance and Low‐Energy‐Loss Ternary Photovoltaics through Judicious Selection of the Third Component

“…[1][2][3][4][5] With the maturing development of donor (D) and acceptor (A) components, the emergence of ternary or even quaternary bulk heterojunction (BHJ) blends has become a new path for improving the PCEs and stabilities of OPVs. [6][7][8][9][10] The mechanisms of operation of ternary OPVs can be classified into energy transfer, charge transfer, parallel-like, and alloy models. The embedding of an additional component (i.e., a third D or A component) into a binary active layer can 1) optimize the blend film morphology, 2) modulate the energy diagram to ensure a greater opencircuit voltage (V OC ), and 3) result in complementary absorption for efficient light harvesting and, thereby, increase the short-circuit current density ( J SC ) of the ternary-blend OPV.…”