Step-by-Step Modulation of Crystalline Features and Exciton Kinetics for 19.2% Efficiency Ortho-Xylene Processed Organic Solar Cells

Highlights A novel fluoro-methoxylated end group for Y-series acceptors is produced, and asymmetric substitution strategy is applied as a step-by-step optimization. 19.24% power conversion efficiency is achieved for industrially compatible solvent ortho-xylene processed organic solar cells. Underlying morphological and photo-physical variation is revealed for device performance difference brought by solvent selection, which could set up a template for future research on similar topics. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01241-z.

N2.The reaction was stirred at -78℃ for 3 h and then CO2 gas was added, The reaction mixture was returned to room temperature and stirred overnight.The mixture was poured into water, and acidified to pH 1-2 by addition of the diluted HCl and extracted with EA for three times.The combined organic phase was washed with water followed by brine.Then the solution was dried over Na2SO4 and concentrated under reduced pressure.The residue as light yellow solid was used directly without further purification.

Synthesis of Compound 2
Compound 2 (2.5 g, 4.31 mmol) was dissolved in acetic anhydride (15 mL), the reaction was stirred at 145 °C refluxed for 2.5 h.Then reaction mixture was cooled to room temperature, triethylamine (8 mL) and tert-butyl acetoacetate (1.22 g, 7.75 mmol) were added dropwise and the reaction was stirred at 75 °C overnight.The reaction mixture was poured over ice with HCl and extracted with DCM, The combined organic phase was washed with water followed by brine.Then the solution was dried over Na2SO4 and concentrated under reduced pressure.The Compound 2 as brown solid was used directly without further purification.

Synthesis of BTP-2BO-SFO
BTP-2BO-CHO (300 mg, 0.257 mmol), IC-FO (155.54 mg, 0.642 mmol) were dissolved in absolute chloroform (20 mL), and pyridine (2 mL) were added.The mixture was deoxygenated with nitrogen for 30 min and then refluxed for 6 h.After cooling to room temperature, the mixture was poured into methanol (150 mL) and filtered.The residue was purified by column chromatography on silica gel using petroleum ether/DCM (1:2) as eluent, yielding a dark blue solid and recrystallization through MeOH/DCM for two times to obtain BTP-2BO-SFO (270 mg, 65%

S2 Characterization
UV-vis absorption spectra were measured using a Shimadzu UV-2500 recording spectrophotometer.AFM measurements were obtained by using a Dimension Icon AFM (Bruker) in a tapping mode.The grazing incidence small/wide angle X-ray scattering (GISAXS/GIWAXS) measurements were carried out with a Ganesha SAXSLAB laboratory instrument using a CuKα X-ray source (8.05 keV, 1.54 Å) and a Pilatus 300K detector.The samples for GIWAXS/GISAXS measurements were fabricated on silicon substrates using the same recipe as for the devices.The incident Nano-Micro Letters S4/S22 angle was 0.4° for GISAXS and 0.2° for GIWAXS measurements, respectively.The sample to detector distance (SDD) was set to 1045 and 95 mm for GISAXS and GIWAXS measurement.For the GISAXS images, the DPDAK software was applied to extract the polymer scattering signals.The transformation to q-space, radial cuts for the in-plane and out-of-plane analysis and azimuthal cuts for the orientation analysis were processed by the MATLAB-based package GIXSGUI.

S3 SCLC Measurements
The electron and hole mobility were measured by using the method of space-charge limited current (SCLC) for electron-only devices with the structure of ITO/ZnO/active layer/PFN-Br-MA/Ag and hole-only devices with the structure of ITO/PEDOT:PSS-TA/active layers/MoOx/Ag.The charge carrier mobility was determined by fitting the dark current to the model of a single carrier SCLC according to the equation: J = 9ε0εrμV 2 /8d 3 , where J is the current density, d is the film thickness of the active layer, μ is the charge carrier mobility, εr is the relative dielectric constant of the transport medium, and ε0 is the permittivity of free space.V = Vapp -Vbi, where Vapp is the applied voltage, Vbi is the offset voltage.The charge carrier mobility was calculated from the slope of the J 1/2 ~ V curves.The thickness of target layer is well controlled identical to that of PV's active layer.

S4 Analysis of Jph vs Veff Relationships
The definition of Jph is the current density under illumination (JL) minus the dark current density (JD), and V0 refers to the voltage value when Jph = 0. Accordingly, Veff = V0 -Vappl, where Vappl represents applied voltage, has a clear meaning.Importantly, when Veff reaches a high value (> 2V) it is normally believed that generated excitons are fully collected, in which Jph is equal to saturated current density (Jsat).Then, we can calculate JSC/Jsat and Jmax/Jsat to describe exciton dissociation (ηdiss) and charge collection (ηcoll) efficiency.Jmax is the Jph at the maximal output point.

S5 UV-vis and PL Spectra Fitting Method
UV-vis and PL spectra are modelled as linear superpositions of basis spectra from individual absorbers: A =Σi bi×i (S1) where A = f(E) is the decadic absorbance, bi = f(E) is the (unitless) basis spectrum of material i, which depends on the irradiated energy E, and si is the spectral weight (in units of eV).The index i ∈ {D, A} comprises the donor and acceptor materials, respectively, if applicable.The basis spectra for each material are given as linear superpositions of sub-bands whose shapes are given by hyperparameters that contain morphology information: bi =Σj bi,j (ai,j, wi,j, ci,j, dc,i,j, hi,j, ni,j), (S2) where the index j ∈ {1o, 1a, 2, 3} comprises contributions from the three lowest energetic-allowed optical transitions.For j = 1, we distinguish between contributions Nano-Micro Letters S5/S22 from an ordered phase and an amorphous phase (suffixes 'o' and 'a', respectively).This picture has been shown to yield good results in P3HT (refs. 55,56),PM6 (ref. 32) and Y6 (ref. 33).We model electron-phonon coupling by assuming one effective vibronic progression as a superposition of Gaussian bands of same width wi,j and fixed energy offset dci,j against the energy ci,j of the (0-0) vibronic transition57 for a given electronic transition and the individual spectral weight given by the Huang-Rhys factor, hi,j, of this effective progression.For donor polymers, we adopt the model of weak H aggregates ('Spano model')58 in which the (0-0) vibronic transition is suppressed by a factor ni,j with respect to the other vibronic transitions of the given progression.We use nonlinear regression (function curve_fit of the Python library scipy) to fit the experimental absorption spectra by tuning the hyperparameters in equation ( 2) and Penrose pseudo matrix inversion (using scipy function lsq_linear) to obtain the overall spectral weights in equation ( 1).However, because there is linear dependence between si and ai,j, we need to fix at least one of these parameters.Thus, we follow the convention that the ordered region of the lowest energetic electronic transition of each material has unity spectral weight: ai,1o ≡ 1 (3) Furthermore, due to spectral congestion in the absorption spectra, we reduced the number of free hyperparameters by fixing nD,1a = nD,1o = 0.5, which is a typical value for donor polymers, and by fixing nA,1a = nA,1o = 1 because the acceptor systems of this work are dominated by strong J aggregates rather than weak H aggregates as would be required by the Spano model.

S6 Transient Absorption Spectroscopy
Transient absorption spectroscopy (TAS) was measured with an amplified Ti:sapphire femtosecond laser (800 nm wavelength, 50 fs, 1 kHz repetition; Coherent Libra) and a Helios pump/probe setup (Ultrafast Systems).The 400 nm pump pulses with a pump fluence of 0.5 or < 3 μJ/cm 2 were obtained by frequency doubling the 800 nm fundamental regenerative amplifier output.The white-light continuum probe pulses were generated by focusing a small portion of the regenerative amplifier's fundamental 800 nm laser pulses into a 2 mm sapphire crystal.

Fig. S13
Fig. S13 Normal distribution of VOC, JSC, and FF, based on at least 10 devices

Fig. S15
Fig. S15 Calculated series resistance and shunt resistance of all systems, and new J-V curves with corrected voltage

Fig. S19
Fig. S19 UV-vis spectra deviation metrices of all neat and blend films

Table S1
Photovoltaic performances of non-halogenated main solvent processed OSCs summary

Table S2
Jph vs Veff relationship derived parametersThe brackets contain averages and standard errors of PCEs based on 20 devices.

Table S3
Calculated parameters for (010) peak from OOP direction