Eco-friendly volatile additive enabling efficient large-area organic photovoltaic module processed with non-halogenated solvent

doi:10.21203/rs.3.rs-3752673/v1

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Eco-friendly volatile additive enabling efficient large-area organic photovoltaic module processed with non-halogenated solvent

https://doi.org/10.21203/rs.3.rs-3752673/v1

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The pursuit of sustainable manufacturing for organic solar cells (OSCs) has prompted the exploration of environmentally friendly, non-halogenated solvents. However, contemporary OSCs processed with these solvents often require the inclusion of toxic halogenated additives to optimize photovoltaic performance. In this study, we devised a processing method that incorporates not only a non-halogenated solvent but also a non-halogenated additive. The introduction of the eco-friendly menthol (MT) effectively mitigates detrimental disordered aggregation during film formation by leveraging its strong polarity to enhance acceptor crystallization, thereby optimizing the donor-acceptor morphology. These advancements ultimately lead to more efficient exciton dissociation and charge carrier transport, resulting in the realization of large-area organic photovoltaic modules (19.31 cm²) with a notable power conversion efficiency (PCE) of 15.74%. To the best of our knowledge, this PCE represents the highest reported value for large-area modules processed with non-halogenated solvents and is comparable to state-of-the-art organic photovoltaic modules processed with conventional halogenated solvents. This research underscores the significant potential of fully non-halogenated processing in achieving sustainable manufacturing for high-performance OSCs.

Scientific community and society/Energy and society/Energy efficiency

Physical sciences/Energy science and technology/Renewable energy/Solar energy/Photovoltaics/Solar cells

In recent years, organic solar cells (OSCs) have garnered significant attention owing to their distinctive advantages, including lightweight properties, wide materials availability, and mechanical flexibility.^1–4 Under laboratory conditions, OSCs have achieved a power conversion efficiency (PCE) exceeding 19%.^5–7 The use of halogenated solvents, such as chloroform and chlorobenzene, in photovoltaic device fabrication is a common practice to ensure favorable miscibility and morphology. Unfortunately, these halogenated solvents pose severe risks to human health and the environment.^8–11 The hazards with toxic solvents are particularly pronounced during the production of large-area organic photovoltaic modules, hindering their practical application in future manufacturing.¹²

As the significance of eco-friendly solvents in the production of photovoltaic devices is widely recognized, considerable efforts have been made to improve the photovoltaic performance of OSCs processed with non-halogenated solvents.^13–16 However, non-halogenated solvents with low polarity usually lead to decreased solubility of organic photovoltaic materials (OPMs), resulting in irregular distribution and severe phase separation during film formation. Halogenated additives, therefore, are used to modulate the film morphology by utilizing the distinct solubility of donors and acceptors.^17–19 Nevertheless, it is worth noting that the widespread use of halogenated additives reintroduces environmental concerns. Moreover, the conventional additives with high boiling point may remain in the active layers after thermal annealing (TA), thereby impeding long-term stability of the photovoltaic devices. The genuinely sustainable manufacture of photovoltaic devices that integrate both solvents and additives has not received sufficient attention thus far.

In this study, we propose a novel approach for fabricating high-performance OSCs in non-halogenated solvent by introducing an eco-friendly volatile additive, menthol (MT). The widely utilized polymer donor PM6 and non-fullerene acceptor BO-4Cl were employed as the photovoltaic materials system. MT effectively alleviates the disordered aggregation of acceptors and enhanced crystallization utilizing the induction of its strong polarity, thus contributing to more efficient exciton dissociation and charge carrier transport. As a result, the PM6:BO-4Cl/MT-based photovoltaic device delivers a PCE of 18.81% processed with non-halogenated solvent o-xylene (o-XY). Building upon these findings, large-area photovoltaic modules were fabricated, attaining a remarkable PCE of 15.74% with an illumination area of 19.31 cm².

Theoretical calculations. The chemical structures of the polymer donor PM6, the acceptor BO-4Cl and the additive MT are depicted in Fig. 1a. MT possesses a strong dipole moment of 1.73 Debye (Fig. 1b) due to the high atomic electronegativity of the oxygen atom, promoting the appearance of prismatic crystals (Figure S1). This characteristic facilitates robust intermolecular interactions with the adjacent molecules. Hence, we conducted density functional theory (DFT) calculations to determine the electrostatic potential (ESP) distribution of PM6, BO-4Cl and MT. The singlet point energy calculations were performed using the latest version of ORCA quantum chemistry software²⁰ (version 5.0.4) with PBE0 functional and def2-SVP basis set. DFT-D3 with BJ-damping was applied to account for weak interactions and improve the accuracy of the calculations. As illustrated in Fig. 1c, the conjugated polymer backbones of PM6 exhibit significant negative charges on their surfaces. Conversely, most of the surface of BO-4Cl carries positive charges, except for the negatively charged regions located on the cyano groups. Due to the polarization effect, the oxygen atoms on the hydroxyl groups naturally carry negative charges. The opposite polarity of charge distribution indicates that the solid additive primarily interacts with the acceptor.

To confirm the presence of intermolecular interactions, we optimized the geometric structures of PM6, BO-4Cl and MT (Figure S2) using the GFN2-xTB method.²¹ Subsequently, we constructed assembled geometric structures of the BO-4Cl:MT combinations. Considering the charge characteristics and steric hindrance, MT exhibits a propensity to interact with the core units (referred to as type1) and the end groups (referred to as type2) of BO-4Cl (Fig. 1d). The binding energies between BO-4Cl and MT are calculated using the formula: ${{E}_{binding}={E}_{complex}-(E}_{BO-4Cl}+{E}_{MT})$. Detailed results of the calculations are provided in Table S1. The combination type2 exhibits a binding energy of -18.788 kcal mol⁻¹, which is higher than the − 17.650 kcal mol⁻¹ of the combination type1. The results indicate that MT tends to bind with the end groups of BO-4Cl, which may have an impact on the crystallization of acceptors. To gain further insight into the interactions between BO-4Cl and MT, we performed non-covalent interaction (NCI) analysis using the Independent Gradient Model (IGM) method.²² The resulting IGM diagram was rendered using VMD.²³ Figure S3 illustrates the NCI graphs of the two BO-4Cl:MT combinations from different perspectives. The blue color represents strong O-H…N and O-H…S hydrogen bonding interactions, while the green represents weak van der Waals attractions and the red represents strong repulsions between molecules. The presence of blue color indicates the formation of strong non-covalent interactions between BO-4Cl and MT.

Molecular properties. The thermogravimetric analysis (TGA) shown in Fig. 2a indicates a complete and instant volatilization of MT at 150℃. While at a typical TA temperature of 100℃, a complete volatilization of MT was observed after one-hour treatment, indicating its favorable volatility. The Fourier transform infrared (FT-IR) results in Fig. 2b show that the characteristic absorption of hydroxyl groups of MT, peated at 3269 cm^− 1, disappears after TA treatment at 50℃ for 10 min. After depositing the PM6:BO-4Cl/MT film, we observed no detectable signals for the hydroxyl group, providing the conclusive evidence for the complete removal of MT during film formation. The UV-vis absorption spectra of pure films and blend films were investigated in Fig. 2c and S4. The absorption peaks of PM6/MT film show no significant changes, suggesting negligible intermolecular interactions between donors and additives. The principal absorption peak of BO-4Cl/MT film displays a redshift of 4 nm compared to that of BO-4Cl film, indicating that the additives primarily influence the intermolecular π-π interaction of acceptors, which is consistent with the computational results as shown in Fig. 1. Meanwhile, the primary peak of PM6:BO-4Cl/MT blend film exhibits a redshift from 818 to 820 nm, probably resulting from the optimization of the donor/acceptor molecular packing in the presence of additives. The analysis of spectral data indicates that MT molecules mainly interact with acceptors and can be readily removed, highlighting its potential as a promising candidate additive for photovoltaic devices.

Photovoltaic performance and charge dynamics. Inspired with the above analysis, OSCs with a configuration of ITO/2PACz/active layer/PFN-Br/Ag were fabricated (Fig. 3a). Figure 3b presents the current density-voltage (J-V) characteristics of PM6:BO-4Cl devices with and without MT under one sun illumination (AM 1.5 G, 100 mW cm^− 2), and the corresponding photovoltaic parameters are summarized in Table 1. The PM6:BO-4Cl control device exhibits a moderate PCE of 18.09% with an open-circuit voltage (V_OC) of 0.853 V, a short-circuit current density (J_SC) of 27.55 mA cm^− 2 and a fill factor (FF) of 76.95%. We optimized the weight ratio (33/67/100 wt%) of MT additive to BO-4Cl acceptor. The results, as illustrated in Figure S5 and Table S2, demonstrate that the device processed with 67 wt% MT additive yields a champion PCE of 18.81%, accompanied by a V_OC of 0.853 V, a J_SC of 28.35 mA cm^− 2 and an FF of 77.76%. As far as we know, the reported efficiency is among the highest for PM6-based binary OSCs processed using non-halogenated solvents (Table S3).^{18,19,24–30} The external quantum efficiency (EQE) spectrum of PM6:BO-4Cl/MT device shows an increased response in the region of 400–800 nm (Fig. 3c), corresponding to the enhancement of J_SC. The J_SC value calculated from the integration of the EQE spectrum was 27.64 mA cm^− 2, which agreed well with the value obtained from the J-V curve within a deviation of 2.6%.

Table 1

Detailed photovoltaic parameters of OSCs under illumination of AM 1.5G, 100 mW cm^− 2.
Conditions	V_OC (V)	J_SC (mA cm^− 2)	J_SC ^EQE(mA cm^− 2)	FF (%)	PCE_max (%)	PCE_avg^a (%)
PM6:BO-4Cl	0.853	27.55	27.07	76.95	18.09	17.71 ± 0.28
PM6:BO-4Cl/MT	0.853	28.35	27.64	77.76	18.81	18.52 ± 0.19

^a Average data were obtained from 16 independent devices.

We plotted the photocurrent density (J_ph) versus the effective voltage (V_eff) curves to gain a deeper understanding of the exciton dissociation and charge extraction processes. J_ph can be defined as J_light – J_dark, where J_light and J_dark are the current densities under illumination and in the dark, respectively. V_eff can be defined as V₀ – V_bias, where V₀ is the voltage at J_ph = 0 and V_bias is the applied voltage. The exciton dissociation probability (P_diss) was calculated as J_ph/J_sat under short-circuit conditions, where J_sat is the saturation photocurrent density. Similarly, the charge collection probability (P_coll) was obtained from J_ph/J_sat under the maximum power output condition. As shown in Fig. 3d and Table S4, the PM6:BO-4Cl/MT device exhibits higher P_diss (98.44%) and P_coll (90.25%) compared to the PM6:BO-4Cl device (97.57% and 89.51%, respectively), indicating more efficient exciton dissociation and charge collection.

The dependence of J_SC and V_OC on the illumination intensity (P_light) was measured to investigate the charge recombination processes. The relationship between J_SC and P_light can be expressed as J_SC ∝ P_light^ɑ, where ɑ represents the exponential factor obtained from the slope of the linear fitting. In Fig. 3e, the PM6:BO-4Cl/MT device exhibits a higher ɑ value (0.998) compared to the PM6:BO-4Cl device (0.992), suggesting a weaker bimolecular recombination. As shown in Fig. 3f, the slopes of V_OC versus P_light decrease from 1.19 kT/q for the PM6:BO-4Cl device to 1.12 kT/q for the PM6:BO-4Cl/MT device (where k is the Boltzmann’s constant, T is the temperature, and q is the elementary charge), indicating the dominance of biomolecular recombination in the PM6:BO-4Cl/MT device. The deviation from the expected kT/q value may be attributed to trap-assisted recombination derived from morphological traps or interfacial defects. These findings suggest that both bimolecular recombination and trap-assisted recombination are significantly suppressed in the MT-assisted devices, accounting for the high J_SC and FF values obtained. Besides, we also performed transient photocurrent (TPC) measurements to gain insights into the carrier dynamics process. As depicted in Fig. 3g, the PM6:BO-4Cl/MT device exhibits a shorter carrier lifetime (0.15 µs) compared to the PM6:BO-4Cl device (0.19 µs), indicating more efficient carrier extraction, which agrees well with the observed charge collection probability in the PM6:BO-4Cl/MT device.

We subsequently investigated the charge transport properties by using the space charge limited current (SCLC) method. As shown in Fig. 3h and Table S5, the PM6:BO-4Cl device exhibits a hole mobility (µ_h) of 5.19 × 10^− 4 cm² V^− 1 s^− 1 and an electron mobility (µ_e) of 1.33 × 10^− 3 cm² V^− 1 s^− 1, resulting in a µ_h/µ_e value of 0.39. Upon the addition of MT to the binary system, the PM6:BO-4Cl/MT device demonstrates an increased µ_h of 5.88 × 10^− 4 cm² V^− 1 s^− 1 and µ_e of 1.42 × 10^− 3 cm² V^− 1 s^− 1. The µ_h/µ_e value slightly increases to 0.41, indicating a more balanced charge carrier mobility. To evaluate the trap state density (N_t) in different devices, the dark current-voltage (I-V) curves of the electron-only devices are plotted in Fig. 3i. At low bias voltage, the current exhibits an ohmic response within the linear region. As the voltage increases, the current enters the intermediate region, where traps become filled by the injected free carriers. The calculated values of N_t are found to be 8.09 × 10¹⁵ cm^− 3 and 6.12 × 10¹⁵ cm^− 3 for the PM6:BO-4Cl and PM6:BO-4Cl/MT devices, respectively. The balanced charge transport and reduced trap state density indicate that MT effectively suppresses charge accumulation and recombination in the active layers, contributing to the improved J_SC and FF in the MT-assisted devices.

Morphology characterization and working mechanism. To explore the effect of MT on the morphology, we examined the miscibility of the blend films through contact angle measurements (Figure S6). According to the Owens-Wendt-Rabel-Kaelble (OWRK) model, the surface tensions (γ) are calculated to be 33.12 and 38.35 mN m^− 1 for PM6 and BO-4Cl films, respectively. Upon the MT addition, the corresponding γ values change to 29.86 and 43.42 mN m^− 1 for the respective films. The interaction parameters (χ) are further calculated according to the Flory-Huggins model, which can be expressed as ${{\chi }}_{\text{1,2}}\propto {(\sqrt{{\gamma }_{1}}-\sqrt{{\gamma }_{2}})}^{2}$. The calculated parameters are summarized in Table S6 and S7. The χ parameter of the BO-4Cl:MT blend (χ = 0.335) is significantly lower than that of the PM6:MT blend (χ = 1.033), indicating that MT exhibits better miscibility with the BO-4Cl molecule. Without the addition of MT, the PM6:BO-4Cl binary blend shows a χ parameter of 0.192, which is lower than that of PM6:(BO-4Cl/MT) blend (χ = 0.696) and BO-4Cl: (PM6/MT) blend (χ = 0.531). The higher χ parameters observed in the MT-assisted blends suggest that MT reduces the miscibility between the donor and acceptor, promoting appropriate phase separation in the binary blend film.

The film surface morphology properties were investigated by the atomic force microscopy (AFM) measurements (as shown in Fig. 4a, 4b and S7). There is no noticeable change in the images of PM6 and PM6/MT films, indicating that MT has a negligible effect on PM6. In contrast, the BO-4Cl/MT film displays uniform pores due to the volatilization of MT, resulting in an increased R_q value from 0.41 to 10.40 nm. These results confirm the uniform mixing of MT and BO-4Cl, aligning with the findings from contact angle measurements. Meanwhile, the PM6:BO-4Cl/MT film exhibits a finer nanofiber network with an R_q value of 1.20 nm comparing with 0.88 nm of the PM6:BO-4Cl film, facilitating more efficient exciton dissociation and charge transport.

In addition, we studied the crystallinity and crystal orientation of the blend films using grazing incident wide-angle X-ray scattering (GIWAXS). The 2D-GIWAXS patterns and the corresponding line cuts are shown in Fig. 4c-4e. The calculated values of d-spacing and crystal coherence length (CCL) for both films are summarized in Fig. 4f and Table S8. The PM6:BO-4Cl film exhibits a lamellar packing (100) diffraction peak at q_xy = 0.272 Å⁻¹ in the in-plane (IP) direction and a strong π-π stacking (010) diffraction peak at q_z = 1.725 Å⁻¹ along the out-of-plane (OOP) direction, manifesting a preferential face-on orientation. Similarly, the PM6:BO-4Cl/MT film shows the (100) and (010) diffraction peaks at q_xy = 0.271 Å⁻¹ and q_z = 1.732 Å⁻¹, respectively. The calculated d-spacing values³¹ estimated from the (100) peaks are 23.100 and 23.185 Å for PM6:BO-4Cl and PM6:BO-4Cl/MT films, respectively. The slightly increased d-spacing values of the lamellar packing may be attributed to the steric hindrance effect of MT. Moreover, the d-spacing values of π-π stacking at (010) peaks decrease from 3.642 to 3.628 Å, implying a more compact molecular packing. Upon the MT addition, the CCL values significantly increase from 38.209 to 71.581 Å for the (100) peaks and from 21.179 to 30.567 Å for the (010) peaks, respectively. These higher CCL values suggest fewer imperfections and dislocations, demonstrating the positive effect of MT in inducing higher crystallinity in the blend films.

Based on the analysis of the interaction between MT and PM6:BO-4Cl heterojunction, a working mechanism of morphological evolution influenced by the volatile additive is proposed (Fig. 4g). During the spin-coating process of the photovoltaic solution onto substrates, the films undergo an initial nucleation process. MT molecules predominantly localize around acceptors and form strong intermolecular interactions via hydrogen bonds. As the solvent evaporates, MT molecules become trapped between acceptors, effectively hindering the disordered aggregation of BO-4Cl molecules and reducing charge recombination. Due to the strong dipole force, MT can induce the ordered molecular arrangement and better crystallization of acceptors, facilitating the long-range charge transfer. Upon complete removal of MT, the blend films exhibit a refined nanofiber morphology with optimal phase separation.

Large-area modules. Furthermore, we manufactured large-area organic photovoltaic modules to evaluate the potential of MT-assisted OSCs for large-scale production. The P1/P2/P3 laser etching method³² was used to connect the anode of one cell to the cathode of the next cell (Fig. 5a). Seven sub-cells are connected in series to form the monolithic modules. Figure 5b presents a photo of the module with a side length of 6 cm. The total illumination area is 19.31 cm², including the photoactive area and the inactive interconnecting area. Due to the laser patterning process, the geometric fill factor can be up to 98%. As depicted in Fig. 5c, the module achieves a remarkable champion PCE of 15.74%, accompanied by a V_OC of 5.945 V, a J_SC of 3.66 mA cm^− 2 and an FF of 72.39%, which is one of the highest values reported to date for large-area organic photovoltaic modules processed with non-halogenated solvents (Fig. 5d and Table S9).^{13,25,33–46} The PCE was also certified with 14.95% efficiency by a third-party accrediting institute (Figure S8). Subsequently, the shelf stability of the champion module was tested in inert atmosphere, it maintained 86% efficiency after 3840 hours aging (Figure S9).

In this work, we have found a non-halogenated volatile additive MT, showing remarkable ability in suppressing the disordered aggregation of acceptors and promoting ordered molecular arrangement. Consequently, the optimized molecular morphology enables a binary OSC with PCE of 18.81%. In addition, we have successfully fabricated the large-area modules (19.31 cm²) employing the same strategy, achieving a PCE of 15.74% (certified as 14.95%). To the best of our knowledge, this efficiency stands among the highest reported for large-area organic photovoltaic modules using non-halogenated solvents. Our work demonstrates the feasibility of using eco-friendly solvents and additives in fabricating high-performance OSCs, thereby paving the way for sustainable manufacturing of organic photovoltaic modules.

Materials. The PM6 (Mw = 90 kDa), BO-4Cl and PFN-Br were purchased from Solarmer Materials Inc. 2PACz was obtained from TCI Development Co., Ltd. Menthol was commercially available from Aladdin Bio-Chem Technology Co., Ltd. O-xylene (o-XY) was purchased from J&K Scientific Ltd. All materials and regents were used without further purification. The pre-patterned indium-tin oxide (ITO)-coated glass substrates were purchased from Materwin New Materials with a sheet resistance of 10 Ω sq^− 1.

Devices fabrication. The OSC devices were constructed with ITO/2PACz/photoactive layer/PFN-Br/Ag. 2PACz was dissolved in ethanol at a concentration of 0.35 mg ml^− 1. PFN-Br was dissolved in methanol at a concentration of 0.5 mg ml^− 1. The mixed PM6:BO-4Cl was dissolved in o-XY at a polymer concentration of 10 mg ml^− 1. The weight ratio of donor to acceptor was 1:1.2. MT was added to the photoactive solution as an additive at different weight ratios (33/67/100 wt% relative to BO-4Cl). All the blend solutions were stirred at 60℃ for 4 h. The ITO-coated glass substrates were cleaned by sequential ultrasonication in soap deionized water, deionized water, acetone, and isopropanol for 10 minutes, respectively. After treatment of oxygen plasma for 20 minutes, the substrates were transferred to a nitrogen-filled glove box. The 2PACz solution was spin-coated at 6000 rpm without thermal annealing. The photoactive solutions were then spin-coated at an optimized speed to obtain active layers with thickness of ~ 105 nm. The films were subsequently thermally annealed on a hotplate at 50℃ for 10 minutes. The PFN-Br solution was then spin-coated onto the active layer at 2500 rpm without any annealing. Finally, 80-nm-thick Ag was deposited as the top electrode by thermal evaporation under less than 5×10^− 5 Pa.

Large-area modules fabrication. For large-area module fabrication, the modules were fabricated with a similar architecture to the small-area OSCs. The series connection is realized using the typical P1-P3 laser patterning method, and the geometric fill factor is 98.25%.

J-V curves and EQE measurement. The J-V characteristics were measured by using the Keithley 2400 source meter under AM 1.5G light (100 mW cm^− 2) from a SAN-EI Electric solar simulator. The light intensity was calibrated using a standard single crystal silicon solar cell. The typical device area of 0.0585 cm² was defined by a shadow mask. For the large-area module, the total illumination area is 19.31 cm². The external quantum efficiency (EQE) spectra were recorded using a measurement system (QE-R) from Enli Technology.

Space-charge-limited-current (SCLC) measurement. The hole and electron mobilities were measured using the SCLC method, employing the device architecture of ITO/2PACz/active layer/MoO_x/Ag and ITO/ZnO/active layer/PFN-Br/Ag, respectively. The mobilities are obtained by fitting the dark current with the following equation:

$$\text{J}=\frac{9}{8}{\epsilon }_{0}{\epsilon }_{r}\mu \frac{{V}^{2}}{{L}^{3}}$$

where J is the current density, ε₀ is the permittivity of vacuum (8.85×10^− 12 F m^− 1), ε_r is the relative permittivity of the material (generally to be 3 for OSCs), µ is the zero-field mobility, V is the effective voltage, L is the film thickness.

The trap state densities (N_t) are calculated from the following equation:

$${N}_{t}=2{\epsilon }_{0}{\epsilon }_{r}\frac{{V}_{TFL}}{{qL}^{2}}$$

where N_t is the trap state density, ε₀ is the permittivity of vacuum (8.85×10^− 12 F m^− 1), ε_r is the relative permittivity of the material (generally to be 3 for OSCs), V_TFL is the onset voltage of the trap-filled limit, q is the elementary charge, L is the film thickness.

Surface tension characterization. Contact angle measurements were carried out using deionized water and diiodomethane with a Dropmeter 100P contact angle system at room temperature. All films were thermally annealed at 50℃ for 10 minutes except the volatile MT film.

The surface tensions (γ) are calculated according to the OWRK model:

$$2\sqrt{{\gamma }_{s}^{d}{\gamma }_{l}^{d}}+2\sqrt{{{\gamma }_{s}^{p}\gamma }_{l}^{p}}={\gamma }_{l}(1+\text{cos}\theta )$$

where ${\gamma }_{l}$is the surface tension of the liquid, ${\gamma }_{l}^{d}$and ${\gamma }_{l}^{p}$ are the dispersion force and polarization force of the liquid, ${\gamma }_{s}^{d}$and ${\gamma }_{s}^{p}$ are the dispersion force and polarization force of the solid.

The interaction parameters (χ) are calculated according to the Flory-Huggins model:

$${{\chi }}_{\text{1,2}}\propto {(\sqrt{{\gamma }_{1}}-\sqrt{{\gamma }_{2}})}^{2}$$

where ${{\chi }}_{\text{1,2}}$ is the interaction parameter, ${\gamma }_{1}$ and ${\gamma }_{2}$ are the surface tension.

Grazing incidence wide-angle X-ray scattering (GIWAXS) characterization. The grazing incidence wide-angle X-ray scattering (GIWAXS) characterization was conducted at TPS 25A1, National Synchrotron Radiation Research Center (NSRRC). The X-ray photon energy of the incident beam is 12.37 keV and the beam size at TPS 25A1 is 5×5 um. The two-dimensional diffraction patterns were recorded by a single photon counting detector, EIGER X 1M. The pixel size of the detector is 75 um.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (62105289). We also thank Prof. U-Ser Jeng (NSRRC) and his group members for their kind assistance in GIWAXS data analysis.

Author contributions

Y. Yang conceived the project. Z. Jia conducted the experiments and data analysis. J. Pan fabricated and characterized the devices. X. Chen and Y. Li helped in the morphology analysis. T. Liu and H. Zhu helped in the spectral data characterization. J. Yao and B. Yan helped in the large-area module fabrication. Y. Yang, Z. Jia and J. Pan contributed to manuscript preparation. All authors discussed the results and commented on the manuscript.

Conflict of Interest

The authors declare no conflict of interest.

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Eco-friendly volatile additive enabling efficient large-area organic photovoltaic module processed with non-halogenated solvent

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