Process‐Aid Solid Engineering Triggers Delicately Modulation of Y‐Series Non‐Fullerene Acceptor for Efficient Organic Solar Cells

Abstract

considered as one of the most promising green-energy technologies. [1][2][3][4] From the past several years, with the advents of start-of-the-art Y-series non-fullerene acceptors (NFAs) (Y6, Y6-BO, BTIC-2Cl-γCF 3 , BTP-eC9, L8-BO, and so on) in terms of novel electron-deficient core, dithienothiophen[3.2-b]pyrrolobenzothiadiazole, BTP, [5][6][7][8][9][10] the recording power conversion efficiencies (PCEs) have exceeded 19% in single-junction configuration and over 20% certified PCE based on tandem solar cells has been reported recently. [11,12] As the exciton splitting, charge generation, transport, and extraction are highly dependent on the microstructure morphology and mesoscopic aggregation state in bulk heterojunction (BHJ) photoactive layer. [13] Correspondingly, considerable morphology control strategies have been proposed to enhance crystallinity and manipulate phase separation behaviors for the promotion of photovoltaic characteristics. For example, solvent additive engineering is a promising approach to fine-tune nanomorphology. Despite the increment of performance, such a strategy worsen the device reproducibility and long-term operational stability due to the low volatilization property. [14][15][16][17] Besides, the ternary blend (introducing a third Volatile solids with symmetric π-backbone are intensively implemented on manipulating the nanomorphology for improving the operability and stability of organic solar cells. However, due to the isotropic stacking, the announced solids with symmetric geometry cannot modify the microscopic phase separation and component distribution collaboratively, which will constrain the promotion of exciton splitting and charge collection efficiency. Inspired by the superiorities of asymmetric configuration, a novel process-aid solid (PAS) engineering is proposed. By coupling with BTP core unit in Y-series molecule, an asymmetric, volatile 1,3-dibromo-5-chlorobenzene solid can induce the anisotropic dipole direction, elevated dipole moment, and interlaminar interaction spontaneously. Due to the synergetic effects on the favorable phase separation and desired component distribution, the PAS-treated devices feature the evident improvement of exciton splitting, charge transport, and collection, accompanied by the suppressed trap-assisted recombination. Consequently, an impressive fill factor of 80.2% with maximum power conversion efficiency (PCE) of 18.5% in the PAS-treated device is achieved. More strikingly, the PAStreated devices demonstrate a promising thickness-tolerance character, where a record PCE of 17.0% is yielded in PAS devices with a 300 nm thickness photoactive layer, which represents the highest PCE for thick-film organic solar cells.

Theoretical investigation of fused N-methyl-dithieno-pyrrole derivatives in the context of acceptor–donor–acceptor approach

“…[11][12][13][14] It has been already reported that the use of non fullerene based semiconducting materials in photovoltaics have increased the PCE up to 18.5%. 12,15,16 Among these, small-molecule acceptors with the acceptor-donoracceptor (A-D-A) backbone architecture, similar to the widely used and rather successful small-molecule donors, have drawn interest due to their easily tunable energy levels and high device performances. Besides, conjugated small molecules have attracted much attention due to their well dened structures and hence less batch to batch variation, easy synthetic control, high mobility and open circuit voltage, high purity, versatile chemical structures and easy energy level control.…”

Isomerization of Noncovalently Conformational Lock in Nonfused Electron Acceptor toward Efficient Organic Solar Cells

“…Organic solar cells (OSCs) have received extensive attention as one of the most promising photovaltiac technologies because of their potential for solution-processed large-area production, flexible and stretchable devices, and semitransparent photovoltaic applications. − The power conversion efficiencies (PCEs) of typical solution-processed bulk heterojunction OSCs have reached over 18% in many systems, which is greatly attributed to the design and synthesis of high-performance nonfullerene small molecular acceptors (SMAs) − and paired electronic donors, − deeper understandings of the charge dynamics, − morphological control, , and device engineering. − Currently, most of the high-efficiency SMA materials are fused-ring electron acceptors (FREAs), such as Y-series SMAs − and ITIC families, − which typically consist of a large ladder-type fused multiring core with bulky side chains and two strong electron-withdrawing end-capped units. The fused-ring core could enhance the light absorption and charge carrier mobilities of FREA because of its π-extended conjugation length and rigid coplanar structures.…”

Effects of the rigid and sterically bulky structure of non-fused nonfullerene acceptors on transient photon-to-current dynamics

“…S1 in the ESI †), [17][18][19][20] and the power conversion efficiencies (PCEs) of the state-of-the-art devices have surpassed 19%. 21 Comprehensive studies, including those on steady state current-voltage, 17,18,[22][23][24] spectroscopic, [25][26][27] and morphological analyses [28][29][30][31][32][33] have revealed that the utilization of a rigid p-conjugated framework and the suppression of face-to-face intermolecular arrangement are advantageous for photoinduced charge generation and isotropic charge transport. However, the utilization of such fused-ring structures has faced difficulties in scale-up synthesis and structural tunability.…”