Crossbreeding Effect of Chalcogenation and Iodination on Benzene Additives Enables Optimized Morphology and 19.68% Efficiency of Organic Solar Cells

Abstract Volatile solid additives have attracted increasing attention in optimizing the morphology and improving the performance of currently dominated non‐fullerene acceptor‐based organic solar cells (OSCs). However, the underlying principles governing the rational design of volatile solid additives remain elusive. Herein, a series of efficient volatile solid additives are successfully developed by the crossbreeding effect of chalcogenation and iodination for optimizing the morphology and improving the photovoltaic performances of OSCs. Five benzene derivatives of 1,4‐dimethoxybenzene (DOB), 1‐iodo‐4‐methoxybenzene (OIB), 1‐iodo‐4‐methylthiobenzene (SIB), 1,4‐dimethylthiobenzene (DSB) and 1,4‐diiodobenzene (DIB) are systematically studied, where the widely used DIB is used as the reference. The effect of chalcogenation and iodination on the overall property is comprehensively investigated, which indicates that the versatile functional groups provided various types of noncovalent interactions with the host materials for modulating the morphology. Among them, SIB with the combination of sulphuration and iodination enabled more appropriate interactions with the host blend, giving rise to a highly ordered molecular packing and more favorable morphology. As a result, the binary OSCs based on PM6:L8‐BO and PBTz‐F:L8‐BO as well as the ternary OSCs based on PBTz‐F:PM6:L8‐BO achieved impressive high PCEs of 18.87%, 18.81% and 19.68%, respectively, which are among the highest values for OSCs.

a JNM-ECZ400S nuclear magnetic resonance spectrometer using CDCl3 as the solvent.
GIWAXS measurements were performed at Complex Materials Scattering (CMS) beamline of the National Synchrotron Light Source II (NSLS-II), Brookhaven National Lab.AFM images were obtained by using a Bruker Inova atomic microscope in tapping mode.TEM images were obtained by using a Thermo Scientific Talos F200S G2 transmission electron microscope.Femtosecond transient absorption (fs-TA) spectroscopy experiments were performed using a home-built system with a Ti: sapphire regenerative amplified laser system (Coherent Legend Elite).The probe beam was generated by focusing part of the fundamental femtosecond laser beam onto a 3-mm-thick sapphire plate or 4 mm-thick Yttrium aluminum garnet plate for visible (vis) and near-IR (NIR) spectral windows, respectively.780 nm laser was used to selectively excite NFAs.TA results in this work were presented in the unit of ΔOD, negative features could reflect ground-state bleaching (GSB) or stimulated emission (SE), a positive signal was an excited-state absorption (ESA).During TA measurements, the samples were kept in nitrogen to avoid photodegradation.The pump fluence was kept at <5 μJ cm -2 to minimize the exciton−exciton annihilation effect.

Device Fabrication and Measurements
Device fabrication: The patterned indium tin oxide (ITO, sheet resistance = 15 Ω square -1 ) glass substrates were sequentially ultrasonicated with detergent, deionized water, acetone and isopropanol.Then, the ITO glasses were treated with UV-ozone for 30 min.Poly(3,4ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (Bay PVP.Al 4083, Bayer AG) was filtrated through a 0.45 μm nylon filter and then spin-coated on the cleaned ITO substrates at 5000 rpm for 60 s to form a thin layer (35 nm).After that, the substrates were baked at 150 oC on a hot plate for 10 min.The PM6:L8-BO solutions (1:1.2 by weight, 16.5 mg/mL in chloroform) or PBTz-F:PM6:L8-BO solutions (x:(1-x):1.2 by weight, 16.5 mg/mL in chloroform) without and with different additives were stirred at room temperature for 2 hours before used.The above solutions were spin-coated on the ITO/PEDOT:PSS substrates at a speed of 3000 rpm for 30 s to form a ~100 nm thickness of the photoactive layer.Then, the substrates were baked at 100 o C for 10 min.PNDIT-F3N solution (0.5 mg/mL in methanol with 5 v% of acetic acid) was spin-coated on the top of the active layer to form a thin cathode interlayer.Finally, argentum electrode (Ag, 100 nm) was deposited under high vacuum (~10 -5 Pa) in an evaporation chamber.For the hole-only devices, after deposition of the photoactive layer on ITO/PEDOT:PSS substrates, molybdenum oxide (10 nm) and Ag electrode (100 nm) were was deposited under high vacuum (~10 -5 Pa) in an evaporation chamber.For the electron-only devices, diethylzinc solution (2 M in toluene diluted by tetrahydrofuran) was spin-coated on the ITO substrates under dry air followed by baked at 200 o C for 30 min, the other fabrication processes were identical to the OSC devices.
The EQE values were measured with an EQ-R solar quantum efficiency test system (Enlitech Co., Ltd., Taiwan, China).All fabrication and characterization processes, except for the HTLs preparation and EQE measurements, were conducted in a high purity argon filled glove box.3. Supplementary Tables Table S1.Charge carrier mobilities of the PM6:L8-BO blends with various additives.

Supplementary Figures
Additive μh

Figure S1 .
Figure S1.Normalized PCEs of the devices without additive and with SIB, DIB additive, respectively, under continuous white light LED illumination.

Figure S2 .
Figure S2.J 0.5 -V curves of the (a) hole-only and (b) electron-only devices.

Figure S3 .
Figure S3.a-f) GIWAXS patterns of PM6 films modified with various additives.g) The corresponding in-

Figure S4 .
Figure S4.a) J-V curves of the PBBTz-Cl:PY-IT based all-PSCs without and with SIB additive

Table S2 .
Summarized parameters for the ordered structures of L8-BO with various additives