Spin-manipulation via novel MoPS_3 nanocrystal for high-performance thick-film organic solar cells

Domain: biology
Published: 2026-03-10
Editorial outcome: major_revision

Abstract
The realization of high-efficiency thick-film organic solar cells (OSCs) is crucial for scalable manufacturing yet remains challenging due to limited exciton diffusion. Here, we introduce a magnetic strategy by incorporating two-dimensional (2D) ferromagnetic MoPS3 nanocrystal into the active layer to manipulate exciton spin dynamics. We demonstrate that the interaction between the ferromagnetic MoPS3 nanocrystal and excitons promotes the formation of weak intrinsic magnetic fields within the active layer. These fields effectively promote the intersystem crossing (ISC) from short-lived singlet excitons to long-lived triplet excitons, thereby extending exciton diffusion length and reducing non-radiative recombination losses. Consequently, MoPS3 nanocrystal doped D18-Cl:L8-BO devices achieve power conversion efficiencies of 20.37% at an active layer thickness of 100 nm and 19.36% (19.13% certified value) at an active layer thickness of 300 nm, representing one of the highest reported values for thick-film (>300 nm) OSCs. Universal applicability is demonstrated with power conversion efficiencies of 20.91%/19.63% (D18:L8-BO) and 19.13%/17.92% (PM6:Y6) at 100/300 nm. This work establishes 2D ferromagnetic MoPS3 nanocrystal as effective spin manipulators in organic semiconductors and provides a universal strategy to overcome the critical thickness-performance trade-off in OSCs.

Introduction
The pursuit of organic solar cells (OSCs) has been driven by their potential for lightweight, flexible, and large-area photovoltaic applications via cost-effective solution-processing techniques1–7. Significant advancements have been achieved with power conversion efficiencies (PCEs) now beyond 20% in state-of-the-art laboratory devices8–12. However, these record efficiencies are invariably obtained from devices with thin active layers (typically ≤100 nm), which are amenable to efficient exciton diffusion and charge collection13,14. For industrial-scale manufacturing using printing and coating techniques, a thicker active layer (≥300 nm) is highly desirable to enhance process tolerance, improve film uniformity over large areas, and ensure robust, defect-free fabrication15,16. Unfortunately, the inherent trade-off between active layer thickness and device performance remains a formidable challenge17–19. In thick-film OSCs, limited charge-carrier mobility and pronounced bimolecular recombination lead to severe photocurrent and fill factor losses, ultimately constraining the PCE20,21.

The core of this limitation lies in the photophysics of the primary photogenerated species: the singlet exciton (S1)22,23. In a thick-film active layer (≥300 nm), the probability of an S1 exciton diffusing from its generation site to the donor/acceptor (D/A) interface for charge separation becomes critically low. This is governed by two intrinsic constraints: a short exciton diffusion length (LD, typically 5–20 nm in organic blends) and a fleeting lifetime on the nanosecond scale. A promising route to overcome this barrier is to populate the triplet exciton (T1) state. T1 excitons exhibit microsecond to millisecond lifetimes due to their spin-forbidden decay, which translates to a substantially longer effective diffusion length, dramatically increasing the probability of successful charge separation in a thick-film active layer24. However, harnessing this potential is non-trivial. The intersystem crossing (ISC) process from S1 to T1 is spin-forbidden in most organic semiconductors due to weak spin-orbit coupling (SOC) inherent in light elements (e.g., C, H, O, N) that constitute these materials, creating a kinetic bottleneck.

In this work, we introduce a materials-based strategy to overcome this spin-dynamic bottleneck. We synthesized a novel two-dimensional ferromagnetic nanocrystal, MoPS3, via chemical vapor transport (CVT) and derived nanocrystals through solvent-assisted ultrasonic exfoliation25–29, and incorporated it as a spin-functional additive. The interaction between the ferromagnetic MoPS3 nanocrystals and photoexcited species promotes the formation of weak intrinsic magnetic fields within the active layer. These fields, synergizing with the enhanced SOC provided by the heavy molybdenum (Mo) atoms, effectively promote the ISC process. This catalyzes the conversion of short-lived singlets into long-lived triplets, thereby extending the LD and suppressing non-radiative energy loss. Remarkably, MoPS3 nanocrystal doped D18-Cl:L8-BO devices achieve a PCE of 20.37% at a 100 nm thickness and retain a high efficiency of 19.36% at 300 nm, ranking among the highest reported for thick-film OSCs. More importantly, the approach demonstrates remarkable generality and thickness tolerance across high-performance systems, for which D18:L8-BO based devices attain PCEs of 20.91% (100 nm) and 19.63% (300 nm), while PM6:Y6-based devices reach 19.13% (100 nm) and 17.92% (300 nm). Our work establishes ferromagnetic MoPS3 nanocrystal integration as a paradigm for designing thickness-resilient, high-efficiency OSCs, directly addressing a key manufacturability obstacle.

Results
MoPS3 bulk crystal was synthesized via CVT using iodine as a transport agent, with the detailed synthetic route summarized in supplementary information (SI). MoPS3 nanocrystals were subsequently obtained in high yield through solvent-assisted ultrasonic exfoliation (Supplementary Fig. 1). X-ray photoelectron spectroscopy (XPS) depth profiling verifies chemical structure of MoPS3 nanocrystal (Supplementary Fig. 2). X-ray diffraction (XRD) patterns exhibited characteristic (001), (002), and (003) reflections at 15.3°, 9.5°, and 30°, respectively, verifying preserved long-range layered ordering (Supplementary Fig. 3). Atomic force microscopy (AFM) revealed a monolayer-dominated morphology with uniform surface topography and a thickness distribution centered around 0.41 nm (Supplementary Fig. 4). High-resolution transmission electron microscopy (HR-TEM) further resolved crystalline domains with lattice spacings of 0.65 nm and 0.31 nm, corresponding to the (001) and (110) planes, respectively (Supplementary Fig. 5). Dielectric and magnetic profiling demonstrated notably high permittivity and permeability, confirming the capability of MoPS3 nanocrystals to modulate exciton-spin interactions (Supplementary Figs. 6-7). The pronounced SOC in MoPS3 nanocrystals, a direct consequence of the heavy Mo element, manifests as significant band splitting and a complete lifting of spin degeneracy (Fig. 1a-c). This strong SOC, primarily driven by the heavy d-orbital of Mo, leads to a substantial reconstruction of the low-energy electronic structure near the Fermi level. These features provide clear evidence for the decisive role of heavy-metal-derived SOC in defining the electronic and magnetic properties of MoPS3 nanocrystals.

The influence of MoPS3 nanocrystals on the intrinsic magnetic field within the D18-Cl:L8-BO system (Supplementary Fig. 8) was examined using a vibrating-sample magnetometer (VSM). Incorporation of MoPS3 into the D18-Cl:L8-BO composite significantly enhanced the saturation magnetization (SA) from 0.66 emu/g to 1.04 emu/g (Fig. 1d), confirming the reinforcement of intrinsic magnetic fields30. To probe the impact on excited states, we investigated the singlet (ES) and triplet (ET) energy levels. The ES values of D18-Cl and L8-BO, determined from absorption and photoluminescence (PL) spectra intersection, were 2.06 eV and 1.47 eV (Supplementary Table 1), respectively. Due to the large singlet-triplet energy gap (ΔEST > 0.82 eV for D18-Cl and > 0.65 eV for L8-BO), phosphorescent emission at 77 K was nearly undetectable for both neat materials (Fig. 1e, f), indicating energetically blocked ISC. In contrast, dilute solutions of D18-Cl:MoPS3 and L8-BO:MoPS3 at 77 K exhibited clear phosphorescence peaks around 690 nm and 945 nm (Fig. 1g-h), corresponding to ET values of 1.80 eV and 1.31 eV, respectively. The resulting ΔEST values were reduced to 0.25 eV and 0.16 eV, respectively, markedly smaller than those of the pristine materials and favorable for efficient ISC from S1 to T1. Notably, the ET of D18-Cl:MoPS3 (1.80 eV) exceeds the ES of L8-BO (1.47 eV), suggesting potential for triplet-to-singlet energy transfer.

The charge-transfer (CT) state energy (ECT) was determined from the low-energy tail of the Fourier-transform photocurrent spectroscopy (FTPS) and electroluminescence external quantum efficiency (EQEEL) spectra (Supplementary Fig. 9; Fig. 1i). The extracted ECT values are 1.34 eV for the pristine D18-Cl:L8-BO blend and 1.35 eV for the MoPS3-incorporated device. In the control system, ECT lies below the triplet energies (ET) of both donor and acceptor, permitting non-radiative recombination loss via triplet-state back-transfer. In contrast, the incorporation of MoPS3 elevates the triplet energy of D18-Cl above ECT, effectively blocking this loss channel. Furthermore, the reduced energy offset between ET and ECT also implies a more competitive forward CT rate from L8-BO triplet excitons to the CT state (Supplementary Table 2). Additional support comes from Urbach energy analysis of the sub-bandgap EQE spectra, which shows a decrease from 23.66 meV to 21.72 meV upon MoPS3 addition, indicating suppressed energetic disorder31. Collectively, these findings demonstrate that MoPS3 nanocrystals serve a dual function: they reduce ΔEST to promote ISC (suppressing geminate recombination) and strategically realign the triplet and CT energy landscape to minimize non-radiative losses.

Triplet exciton generation, diffusion and dissociation
Electron paramagnetic resonance (EPR) spectroscopy provides direct evidence for the MoPS3-mediated modulation of triplet exciton generation. In the absence of MoPS3, the superoxide radical signal that resulting from the reaction of T1 excitons with oxygen is weak and broadened (Fig. 2a), indicating low ISC efficiency and limited T1 yield. Meanwhile, the singlet oxygen signal originating from direct S1-oxygen interaction is relatively intense and broad, reflecting that most S1 excitons are lost non-radiatively. Upon incorporation of MoPS3, the superoxide radical signal increases markedly and sharpens (Fig. 2b), which may be attributed to the Mo heavy-atom effect enhancing SOC and thus accelerating ISC. Correspondingly, the singlet oxygen signal is substantially suppressed, demonstrating efficient S1 to T1 conversion. Transient absorption (TA) spectroscopy (Fig. 2c, d) conclusively establishes MoPS3 nanocrystal-mediated triplet exciton generation and accelerated ISC within the D18-Cl:L8-BO system. Near-IR kinetics (1200 nm) assigned to T1 → Tn transitions show extended triplet lifetime from 802 ps (pristine D18-Cl:L8-BO) to 1198 ps (MoPS3 nanocrystal doped D18-Cl:L8-BO), confirming interfacial stabilization of triplets (Fig. 2e).

The generation of triplet excitons extends the LD. Excitation-fluence-dependent TA measurements were performed (Fig. 3a, b). The calculated LD values increased from 16 nm (pristine D18-Cl) to 25 nm (D18-Cl:MoPS3) and from 21 nm (neat L8-BO) to 37 nm (L8-BO:MoPS3), confirming enhanced exciton diffusion in MoPS3 nanocrystal-doped phases. MoPS3 nanocrystal incorporation elevated hole (μh) and electron (μe) mobility in both individual and blended films (Supplementary Figs. 10–13; Supplementary Tables 3 and 4), indicating effective promotion of charge transport pathways32. In the D18-Cl:L8-BO blend (~100 nm), both μh and μe are enhanced from 1.16 × 10−3 and 1.31 × 10−3 to 2.21 × 10−3 and 2.09 × 10−3 cm2V−1s−1 upon MoPS3 incorporation. Notably, when the thickness increases to ~300 nm, the pristine blend suffers a severe mobility reduction (μh = 0.38 × 10−3 and μe = 0.42 × 10−3 cm2V−1s−1), whereas the MoPS3-modified film maintains high and well-balanced mobilities (μh = 1.86 × 10−3 and μe = 1.77 × 10−3 cm2V−1s−1). This thickness-robust and balanced charge transport effectively suppresses space-charge accumulation and recombination losses, enabling efficient charge extraction in thick-film active layers. Complementary transient photovoltage (TPV) measurements (Supplementary Fig. 14) under open-circuit conditions independently assessed LD via the Einstein-Smoluchowski relation: LD = (μτkT/q)1/2, where μ indicates charge-carrier mobility, k denotes the Boltzmann constant, and q stands for the elementary charge. Fitting TPV decays [y = Aexp(−x/τ)] yielded longer lifetimes for MoPS3 nanocrystal doped D18-Cl:L8-BO devices (1.61 μs vs. 1.00 μs control)33, corresponding to LD enhancements from 55 nm to 96 nm (D18-Cl) and 58 nm to 93 nm (L8-BO). Although the absolute LD values derived from the ensemble-averaged TPV method and the local-probe EEA analysis are not directly comparable, both techniques consistently demonstrate a substantial increase in the LD upon MoPS3 incorporation (Supplementary Fig. 15). These findings are corroborated by time-resolved photoluminescence (TRPL), which showed an extended average fluorescence lifetime from 0.26 ns to 0.39 ns upon MoPS3 incorporation (Supplementary Fig. 16). Complementary TA spectroscopy under 800 nm excitation (L8-BO selective) revealed exciton dynamics. Collective analysis of 2D color plots (Supplementary Fig. 17), TA spectra (Fig. 3c, d), and ground-state bleaching (GSB) kinetics (Fig. 3e, f) demonstrates synchronized decay of L8-BO GSB (798 nm) with D18-Cl GSB rise (587 nm), providing direct evidence of hole transfer from L8-BO to D18-Cl. Biexponential fitting resolved two lifetime components: τ1 (exciton dissociation lifetime at D/A interfaces) and τ2 (exciton diffusion lifetime to D/A interfaces). Notably, MoPS3 nanocrystal incorporation significantly boosted these exciton lifetime constants at both D18-Cl (τ1 increased from 1.78 ps to 2.15 ps and τ2 from 25.39 ps to 29.95 ps) and L8-BO (τ1 increased from 1.23 ps to 1.35 ps and τ2 from 15.16 ps to 19.70 ps). This extension aligns with the enhanced exciton diffusion lengths. The control device showed a maximum exciton generation rate (Gmax) of 1.74 × 1028 m−3s−1 and an exciton dissociation efficiency [P(E,T)] of 97.2%. MoPS3 incorporation elevated these to 1.75 × 1028 m−3 s−1 and 97.6%, respectively (Supplementary Fig. 18; Supplementary Table 5)34,35. Time-dependent density functional theory (TD-DFT) simulations examined the photoexcitation characteristics (Supplementary Fig. 19). The molar absorptivity increased from 9.1 × 104 L mol⁻1 cm⁻1 (pristine) to 1.30 × 105 L mol⁻1 cm⁻1 (MoPS3-doped), with a red-shifted excitation energy and increased oscillator strength. Hole-electron distribution mapping showed that MoPS3 doping markedly increased and continuouslized the charge density networks (Supplementary Figs. 20-23). Calculations of the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels using a polarization functions (DZVP-MOLOPT-SR-GTH) in a hybrid Gaussian/plane method (Supplementary Figs. 24-25) quantified the electronic structure modification. The HOMO-LUMO gap narrowed upon MoPS3 nanocrystal incorporation, which may strengthen donor-acceptor orbital overlap, reduce the exciton dissociation barrier, and extend the excited-state lifetime, thereby promoting charge separation.

Photovoltaic and photophysical properties
To systematically assess photovoltaic implications, we fabricated control and MoPS3 nanocrystal doped D18-Cl:L8-BO devices with architecture of ITO/2PACz/active layer/PNDIT-F3N/Ag (Supplementary Fig. 26). Current density-voltage (J-V) characterization (Fig. 4a) show the reference D18-Cl:L8-BO device (100 nm active layer) delivers a PCE of 18.97%, with open-circuit voltage (VOC) of 0.92 ± 0.01 V, short-circuit current density (JSC) of 26.19 ± 0.64 mA cm−2, and fill factor (FF) of 76.34 ± 1.23%. Increasing thickness to 300 nm degrades PCE to 16.79%, primarily from FF reduction (69.12 ± 0.88%). Conversely, optimized MoPS3 nanocrystal (0.6 wt%) doped D18-Cl:L8-BO devices (100 nm active layer) achieve peak PCE of 20.37% (VOC = 0.92 ± 0.01 V, JSC = 27.45 ± 0.73 mA cm−2, FF = 79.63 ± 0.68%), as detailed in Table 1 and Supplementary Table 6. This optimum is consistent with the concentration-dependent SCLC results, in which 0.6 wt% MoPS3 nanocrystal incorporation yields enhanced and balanced charge mobilities (Supplementary Fig. 27). Critically, 300 nm MoPS3 nanocrystal doped D18-Cl:L8-BO devices retain a PCE of 19.36% (VOC = 0.92 ± 0.01 V, JSC = 27.24 ± 0.86 mA cm−2, FF = 76.41 ± 0.82%), exhibiting exceptional thickness tolerance (Fig. 4b). This 19.36% efficiency was certified at 19.13% (Supplementary Fig. 28), standing as the record-high for 300 nm-thick OSCs (Fig. 4c; Supplementary Table 7). External quantum efficiency (EQE) spectra (Fig. 4d) confirm enhanced photoresponse across wavelengths for MoPS3 nanocrystal doped D18-Cl:L8-BO devices at both thicknesses versus undoped counterparts. To assess operational resilience, we tracked parameter evolution under thermal stress (50°C), LED illumination, and extended N2 storage (Supplementary Fig. 29; Supplementary Tables 8−13). After 1008 h, MoPS3-doped devices consistently showed higher PCE retention than controls across all conditions.

Charge recombination and extraction dynamics were further examined. The relationship VOC ∝ nkT/q ln Plight (k: Boltzmann constant, T: absolute temperature, q: elementary charge) reflects diminishing trap-assisted recombination as the ideality factor n approaches unity36. Linear regression yielded slopes of 1.21 kT/q (control) versus 1.16 kT/q (MoPS3 nanocrystal doped) devices (Supplementary Fig. 30a), signifying mitigated trap-assisted recombination with MoPS3 nanocrystal integration. Complementarily, the power exponent S in JSC ∝ (Plight)S indicates recombination kinetics, where S ≈ 1 corresponds to minimal bimolecular losses37. Fitting yielded S = 0.89 for control D18-Cl:L8-BO devices and S = 0.91 for MoPS3 nanocrystal doped D18-Cl:L8-BO devices (Supplementary Fig. 30b), indicating restrained bimolecular recombination in MoPS3 nanocrystal doped devices. Charge recombination dynamics were examined via transient photocurrent (TPC) measurements38,39. The extracted charge transport times decreased from 0.39 μs (control D18-Cl:L8-BO device) to 0.37 μs (MoPS3 nanocrystal doped D18-Cl:L8-BO device), confirming accelerated charge extraction enabled by MoPS3 nanocrystal (Supplementary Fig. 31)40. Temperature-dependent PL spectroscopy quantified energetic disorder via a Marcus-Levich-Jortner framework (Fig. 4e-h; Supplementary Figs. 32–33; Supplementary Tables 14−15)41. The D18-Cl:MoPS3 and L8-BO:MoPS3 blends exhibited smaller low-frequency reorganization energy (λ) compared to their neat counterparts (Fig. 4i), demonstrating that MoPS3 suppresses non-radiative recombination by reducing dynamic disorder.

Molecular anchoring mechanism analysis
Ab initio molecular dynamics (AIMD) simulations quantified interaction energies (E) to evaluate interfacial affinity (Supplementary Fig. 34). The computed E for MoPS3/D18-Cl (−23.83 eV) and MoPS3/L8-BO (−20.12 eV) were comparably strong. The interaction energy for the pristine D18-Cl:L8-BO blend was −13.44 eV, which shifted to −4.01 eV upon MoPS3 incorporation. This decrease implies that MoPS3 promotes spatial decoupling between the donor and acceptor phases. Fourier transform infrared (FTIR) and XPS spectroscopy probed interaction sites. FTIR analysis of D18-Cl films reveals MoPS3 nanocrystal selectively coordinates chlorine atoms via S···Cl halogen bonding, marked by attenuation of the C-Cl vibrational mode at 824 cm−1 (Fig. 5a; Supplementary Fig. 35). This aligns with the decreased Cl 2p binding energy (from 200.7 eV to 200.4 eV) and S 2p binding energy (from 164.2 eV to 163.9 eV) (Supplementary Fig. 36). Such position-selective coordination promotes D18-Cl crystallinity through nanocrystal-directed molecular alignment. Conversely, L8-BO films exhibit complete C=O peak suppression at 1159 cm−1 alongside a broad emergent feature at 1103 cm−1 (Fig. 5a; Supplementary Fig. 37), coupled with a 1.2 eV O 1s binding energy decrease, directly evidencing Mo-O coordination between Mo6+ sites in MoPS3 nanocrystal and oxygen atoms in L8-BO. Significantly, asynchronous >1 eV decreases in S 2p, C 1s, N 1s, and F 1s binding energies (Supplementary Fig. 38) upon the incorporation of MoPS3 nanocrystal suggests bidirectional charge transfer: initial electron donation from L8-BO oxygen to Mo6+ is partially back-transferred to L8-BO’s π-system via Mo-S bonds, elevating its electron density.

The impact on molecular packing was investigated using two-dimensional grazing incidence wide-angle X-ray scattering (GIWAXS). MoPS3 incorporation reduced the out-of-plane (OOP) π-π stacking distance for both D18-Cl (from 4.142 Å to 4.009 Å) and L8-BO (from 3.959 Å to 3.944 Å) and increased their crystal coherence lengths (CCL), indicating denser, more ordered packing (Supplementary Figs. 39-41; Supplementary Tables 16−17)42,43. This ordering persisted in the blend film (Fig. 5b). Both control and MoPS3-doped blend films exhibited a preferred face-on orientation. MoPS3 sharpened and intensified the OOP (010) π-π stacking peak (q from 1.546 Å−1 to 1.577 Å−1), corresponding to distances of 4.064 Å and 3.985 Å, respectively, and increased the CCL from 2.719 nm to 3.821 nm (Supplementary Table 18). The reduced π-π distance and increased CCL confirm enhanced π-orbital coherence and crystallinity (Fig. 5c). Spectroscopic signatures (vibronic coupling ratio44, PL intensity45) further corroborated improved molecular ordering in both components (Supplementary Fig. 42), consistent with AFM and TEM results (Supplementary Fig. 43).

In situ absorption spectroscopy reveals distinct film formation dynamics during spin coating of D18-Cl:L8-BO and D18-Cl:L8-BO:MoPS3 blends (Fig. 5d). The pristine film shows a rapid rise and red shift of the long-wavelength absorption within ~0.5 s, indicating accelerated acceptor aggregation and abrupt solidification, while donor-related absorption evolves more gradually. In contrast, the MoPS3-containing film exhibits a smoother and delayed absorption evolution across the entire spectral range, with suppressed abrupt transitions during the critical solidification stage (Supplementary Fig. 44). This moderated kinetics suggests that MoPS3 retards excessive acceptor aggregation and synchronizes donor–acceptor ordering, thereby extending the molecular rearrangement window and promoting more homogeneous film formation. Photo-induced force microscopy (PiFM) was used to probe the nanoscale chemical morphology of the active layers (Fig. 5e). The pristine D18-Cl:L8-BO film exhibits relatively coarse fibrillar networks at both 1455 cm−1 (L8-BO) and 1532 cm−1 (D18-Cl), with average fibril diameters of ~25 nm, indicative of less confined phase separation. Upon incorporation of MoPS3, both donor- and acceptor-rich fibrils become significantly thinner (~21 nm) with narrower diameter distributions (Fig. 5f; Supplementary Fig. 45), reflecting a more uniform and finely interpenetrating morphology. Such refined domain sizes are expected to reduce carrier trapping and non-radiative recombination at donor–acceptor interfaces, consistent with the suppressed non-radiative losses.

Generality of MoPS3 nanocrystal integration for thick-film OSCs
To validate universal thickness tolerance, we incorporated MoPS3 into D18:L8-BO and PM6:Y6 blends. MoPS3 incorporation significantly enhanced saturation magnetization in both systems (Fig. 6a, b; Supplementary Fig. 46). Phosphorescence measurements confirmed that MoPS3 markedly reduced ΔEST for all components (D18, L8-BO, PM6, Y6), promoting efficient ISC (Supplementary Figs. 47-49; Tables 19-20). ECT analysis and Urbach energy decreases confirmed suppressed non-radiative losses and energetic disorder in both MoPS3-modified systems (Fig. 6c; Supplementary Figs. 50-51; Supplementary Tables 21-22). In both control systems, ECT lies below the ET of donor and acceptor, permitting loss via triplet back-transfer. MoPS3 elevates the donor triplet energy above ECT, effectively blocking this channel (Fig. 6d). SCLC analysis confirmed substantial charge mobility enhancements in both systems following MoPS3 integration (Supplementary Figs. 52-55; Supplementary Tables 23-24). TPV measurements provided longer decay times and correspondingly longer calculated LD values for all components (D18, PM6, L8-BO, Y6) in MoPS3-doped devices (Fig. 6e; Supplementary Fig. 56-57). These results demonstrate the universal applicability of MoPS3 for promoting ISC and extending exciton diffusion length.

Photovoltaic metrics for devices across 100–300 nm active layers are shown in J–V curves (Fig. 6f-g; Supplementary Figs. 58-59). The reference D18:L8-BO device (100 nm active layer) delivered a PCE of 19.92%, with a VOC of 0.92 ± 0.01 V, JSC of 27.05 ± 0.71 mA cm−2, and FF of 79.27 ± 0.74%. Performance dropped to 17.59% at an active layer thickness of 300 nm due to FF attenuation (70.21 ± 0.82%). The 0.6 wt% MoPS3 nanocrystal incorporated D18:L8-BO device demonstrated optimal performance with an active layer of about 100 nm (PCE = 20.91%, VOC = 0.92 ± 0.01 V, JSC = 27.69 ± 0.57 mA cm−2, FF = 81.02 ± 0.78%; Supplementary Table 25), as well as maintained a PCE of 19.63% at an active layer thickness of 300 nm (with VOC of 0.92 ± 0.01 V, JSC of 27.82 ± 0.54 mA cm−2, and FF of 76.93 ± 0.67%; Supplementary Table 26), exhibiting excellent film thickness insensitivity. Similarly, PM6:Y6 devices retained 17.92% PCE at 300 nm (vs. 19.13% at 100 nm active-layer thickness) with 0.6 wt% MoPS3 nanocrystal integration (Supplementary Tables 27 and 28).

Methods
Materials sources
Organic semiconductors, including PM6, Y6, L8-BO, and PNDIT-F3N, were purchased from Nanjing Zhiyan Technology Co., Ltd. D18 was obtained from Shenzhen Ruixun Optoelectronic Material Technology Co., Ltd. D18-Cl was sourced from eFlexPV Limited Tech. Co., Ltd. High-purity solvents (e.g., chloroform, CF) and material 2PACz were procured from Sigma-Aldrich.

OSC device fabrication
Patterned indium tin oxide (ITO)-coated glass substrates were cleaned sequentially with detergent, deionized water, acetone, and isopropyl alcohol under sonication (20 min each), followed by overnight drying in an oven. After 5 min of oxygen-plasma treatment, a 2PACz solution in ethanol was spin-coated onto the ITO substrates at 3000 rpm for 30 s and then annealed at 100 °C for 8 min. For the D18-Cl:L8-BO system, the donor:acceptor (D:A) mass ratio was optimized to 1:1.2 (w/w). The concentration of D18-Cl was fixed at 6 mg/mL in chloroform. Active layers with nominal thicknesses of ~100 nm and ~300 nm were deposited via spin-coating at 3500 rpm and 2000 rpm for 30 s, respectively. For the PM6:Y6 system, the optimized D:A mass ratio was 1:1.5 (w/w), with a PM6 concentration of 7 mg/mL in chloroform. Spin-coating at 4000 rpm and 2500 rpm for 30 s yielded films of ~100 nm and ~300 nm, respectively. For the D18:L8-BO system, the optimized D:A mass ratio was 1:1.4 (w/w), with a D18 concentration of 3.5 mg/mL in chloroform. Films with thicknesses of ~100 nm and ~300 nm were obtained by spin-coating at 2000 rpm and 1300 rpm for 30 s, respectively. A 30-second spin-coating process at 2000 rpm forms a uniform thin film around 100 nm thick, whereas spin-coating at 1300 rpm for 30 seconds produces a homogeneous film roughly 300 nm in thickness. Subsequently, a methanol solution of PNDIT-F3N (0.5 mg/mL) was spin-coated at 2000 rpm for 30 s to form the cathode interlayer. Finally, a 100 nm-thick Ag electrode was thermally evaporated under high vacuum (<1 × 10−4 Pa). The effective device area was 0.0516 cm2, which was further defined as 0.04 cm2 using a square metal mask.

Fabrication and characterization of single-carrier devices
Hole-only and electron-only devices with structures of ITO/2PACz/active layer/Ag and ITO/ZnO/active layer/PNDIT-F3N/Ag, respectively, were fabricated to evaluate charge-carrier mobility. Dark current J–V characteristics were measured using a Keithley 2450 source meter. Mobilities were extracted by fitting the SCLC region using the equation: J = (9/8)ε0εrμVeff2/d3, where the parameters are defined as follows: J is the current density, μ is the zero-field charge mobility, ε0 is the permittivity of free space, εr is the relative permittivity of the material, d is the thickness of the active layer, and Veff is the effective voltage.

Instrumentation
UV–vis–NIR absorption and PL spectra were recorded on an APL-ASII spectral analysis system. J–V characteristics of photovoltaic devices were measured under simulated AM 1.5G illumination using a Zolix Sirius-SS150A solar simulator and a Keithley 2450 source meter, calibrated with a certified silicon reference cell. EQE spectra were obtained using a Zolix-built EQE measurement system calibrated with a certified silicon reference cell. TA spectra were acquired by probing differential transmission before and after excitation with an 805 nm pump pulse. TPC and TPV were measured using a CEL-TPV2000 system. AFM images were taken on a Bruker Multimode 8 microscope in tapping mode. TEM was performed on a JEOL JEM-F200 microscope. XRD patterns of MoPS3 nanocrystals were collected on a Bruker D8 Advance diffractometer using Cu Kα radiation (λ = 0.15418 nm). GIWAXS measurements were conducted on a Xeuss 2.0 system (λ = 1.54189 Å). XPS was performed on a Thermo Fisher Nexsa spectrometer. In-situ absorption spectrum were collected using a Maya 2000 Pro spectrometer (Ocean Insight) with illumination from a xenon lamp source. PiFM results were acquired using a VistaScope microscope from Molecular Vista inc. from Songshan Lake Materials Laboratory. PiFM experiments were excited by a pulsed quantum cascade laser (Block Engineering) with a gap-free narrowband tunable wavenumber of 760-1950 cm−1. The spectral line width is ~2 cm−1 with a wavenumber resolution of 0.5 cm−1.

SOC calculations
SOC calculations are performed using the Vienna ab initio simulation package (VASP) by DFT theory calculations. The exchange correlation functional is parametrized by the Perdew, Burke, and Ernzerhof (PBE) model. For the structural relaxation, a cutoff energy of 450 eV is used. A 3×3×1 Monkhorst-Pack K-mesh is used to sample the two-dimensional Brillouin zone. The energy convergence threshold is 1.0 × 10−5 eV and the criteria for the convergence of the Hellmann-Feynman forces on the atoms is 0.02 eV/Å.

AIMD and TDDFT calculations
AIMD simulations were performed using the CP2K software package to investigate the structural evolution of D18-Cl and L8-BO molecules in the presence and absence of MoPS3. The E between D18-Cl and L8-BO were computed for both scenarios. A sufficiently large vacuum thickness was applied along the non-periodic direction to eliminate spurious interactions between periodic images, ensuring that the calculated results were solely governed by the sampled k-points in reciprocal space. Electronic structure calculations were conducted within the framework of DFT using CP2K. The Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional was employed to describe electron–electron interactions. All simulations utilized a double-ζ valence polarized basis set (DZVP-MOLOPT-SR-GTH) for geometry optimizations and energy evaluations of the D18-Cl and L8-BO systems, with and without MoPS3. The optical absorption spectra and electronic excited-state properties were investigated using TDDFT calculations in CP2K with the same DZVP-MOLOPT-SR-GTH basis set. A total of 50 excited states were computed under periodic boundary conditions. Subsequent wave function analysis for the excited states was carried out using the Multiwfn software package.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors report a conceptually new approach to the long-standing “thick-film efficiency cliff” in organic solar cells (OSCs): embedding two-dimensional MoPS3 nanocrystals as a spin-manipulating dopant to convert short-lived singlet excitons into long-lived triplets via magnetically promoted intersystem crossing (ISC). Achieving >19% power-conversion efficiency (PCE) at 300 nm active-layer thickness-while retaining >20% at 100 nm-sets a new benchmark for thick-film OSCs and, if fully substantiated, would constitute a breakthrough for scalable, roll-to-roll manufacturing. The work is therefore potentially suitable for Nature Communications after minor revision. Below I summarize the strengths and the critical issues that must be addressed:\n1. Given the central conclusion that MoPS3 nanocrystals suppress recombination in thick-film (~300 nm) devices, it would be valuable to include SCLC mobility measurements specifically for these thick films to directly substantiate the performance enhancement mechanism.\n2. The exciton diffusion lengths derived from EEA-TA and TPV differ by nearly a factor of two. Although this was mentioned, it would be helpful to more explicitly emphasize in the main text that the two methods show consistent trends but are not directly comparable.\n3. The same concept is referred to with different terms (e.g., “internal magnetic field” and “intrinsic magnetic field”). To avoid confusion, please select and adhere to one consistent term throughout the manuscript.\n4. Some grammatical issues related to singular and plural usage require attention. For instance, “evidences” should be corrected to “evidence,” and subject-verb agreement should be ensured with collective nouns like “data.” A thorough proofread to correct these inconsistencies is recommended. Additionally, some sentences are overly long (e.g., the final sentence of the abstract). Consider splitting lengthy sentences to enhance clarity and readability.\n5. There is a discrepancy in the PCE value of the 300-nm-thick PM6:Y6-based device: 17.92% in the abstract versus 18.33% in the conclusion. We recommend verifying and unifying these values throughout the manuscript.\n6. The material MoPS3 is labeled as both \"antiferromagnetic\" and \"ferromagnetic,\" which creates a contradiction with the description in the main text and abstract.\n7. A schematic summary figure illustrating the relationship between structural tuning and performance enhancement would significantly enhance the manuscript's clarity and impact.\n8. The thick-film OSCs summarized in the Supplementary Table S6 are not sufficient. Some recent important papers should be included, such as Nature Materials 24, 444–453 (2025); and Joule 9, 102135 (2025).", "reviewer_2": "This paper reports a spin manipulation strategy based on two-dimensional magnetic MoPS3 nanocrystals, which successfully enhances internal magnetic fields of the active layer and thus boosting the performance of thick-film organic solar cells (OSCs). The research design is novel, the experimental data are substantial, and the analytical methods are comprehensive, particularly the systematic study of exciton spin dynamics, which holds significant scientific value. The paper is logically structured, rich in figures and tables, and presents reliable conclusions, offering important insights for promoting the scalable manufacturing of thick-film OSCs. Therefore, I recommend the publication of this paper in Nature Communications after minor revisions.\n1. I noticed that MoPS3 has a strong interaction force with the donor/acceptor. Therefore, I suggest that the author test AFM-IR (PiFM) to verify whether MoPS affects the phase separation morphology or fibrotic orientation of the donor/acceptor?\n2. Does MoPS3 affect the film-forming and crystallization kinetics of the active layer? It is suggested that the author supplement in situ absorption to verify this point.\n3. Please add some newly published references in 2025 related to \"Thick-film OSCs\".\n4. Please check and standardize the formatting of references, including journal title abbreviations and the use of punctuation.\n5. Please unify the usage of 'thick-film' and 'thick active layer' throughout the text.\n6. The abstract describes MoPS3 as 'antiferromagnetic', while in the main text it is repeatedly referred to as 'ferromagnetic?\n7. The test temperature is an important factor affecting the value of saturation magnetization. Fig. 1b shows that the saturation magnetization of the film increases after doping with MoPS3, but the temperature conditions during the test are not specified.\n8. There are some sentences in the text that have grammatical errors and need to be corrected. For example, line 3 on page 8, line 4 on page 14, line 15 on page 17, etc.\n9. The unit of the horizontal coordinate of TRPL in Fig. S13 should be on the order of ns. The author should check and confirm the unit markings used during the drawing of Fig. S13.\n10. The authors should provide a specific method to calculate the exciton diffusion length using TPV method in the SI.\n11.The authors have previously reported a Mn-based system. What is the main improvement of Mo-based nanosheet and why?", "reviewer_3": "The \"thickness-efficiency bottleneck\" is a well-known and persistent limitation preventing OSCs from achieving simultaneously high efficiency, mechanical robustness, and compatibility with low-cost, large-area printing techniques. Most previous approaches have focused on optimizing morphology or developing new donor/acceptor materials. This work breaks from convention by introducing a spin-engineering paradigm. The authors propose and meticulously demonstrate a novel strategy employing two-dimensional (2D) magnetic MoPS3 nanocrystals as a spin-state modulator for excitons. The core concept by using magnetic materials to influence excitonic spin dynamics and thereby reducing recombination losses in thick active layers is not only original but also elegantly executed. The experimental framework is exceptionally comprehensive, integrating advanced material synthesis, thorough morphological and spectroscopic characterization, detailed device fabrication, and robust physics-based analysis. As a result, the reported device performance parameters represent a state-of-the-art achievement for thick-film OSCs, setting a new benchmark in the field. The manuscript is well-organized, the data is convincingly presented, and the conclusions are strongly supported by the evidence. It seamlessly bridges fundamental spin physics science with applied device engineering, offering profound insights with significant implications for the future of high-throughput, roll-to-roll processed OSCs. Therefore, I am enthusiastic about the potential of this work for publication in Nature Communications. Its novelty, depth, and technical quality align perfectly with the journal's scope. I recommend acceptance pending minor revisions, which are intended to further polish the narrative, clarify a few key points for a broad interdisciplinary readership, and solidify the manuscript's already strong impact.\n1. The definition of the internal magnetic field should be further quantified.\n2. For Figures 1c–f, please explain the rationale for determining the S1 energy level from the intersection of absorption and fluorescence spectra, whereas the T1 energy level is assigned based on the phosphorescence peak position. Furthermore, it is advisable to convert the abscissa to energy units to facilitate inspection.\n3. The paper optimizes and analyzes the effect of MoPS3 doping concentration on device performance, but lacks direct evidence for the mobility variation under different doping concentrations. I suggest the authors supplement relevant mobility data to strengthen the physical support for the conclusion of doping optimization.\n4. In the morphology discussion part, the influence of MoPS on the crystallization kinetics of the photosensitive layer should be added to demonstrate the effect on the film-forming mechanism. Meanwhile, the key GIWAXS parameters, such as d-spacing distance and crystalline coherence length in Figure 5.\n5. Some recently published work on thick-film organic solar cells is missing from the references in the introduction part."}, "author_response": "Our response: Thank you very much for your time and effort on our manuscript. According to the reviewer’s suggestion, we have included SCLC mobility measurements specifically for these thick films to directly substantiate the performance enhancement mechanism. For ~100 nm films, incorporation of MoPS markedly enhances both hole and electron 3 mobilities, increasing μ from 1.16 × 10−3 to 2.21 × 10−3 cm2 V−1 s−1 and μ from 1.31 h e × 10−3 to 2.09 × 10−3 cm2 V−1 s−1, while maintaining good charge balance. Notably, in thicker (~300 nm) devices, the pristine blend suffers from a pronounced mobility reduction, whereas the MoPS -modified film retains high and well-matched mobilities 3 (~1.8 × 10−3 cm2 V−1 s−1). This thickness-insensitive and balanced charge transport is expected to mitigate space-charge accumulation and recombination losses, thereby enabling efficient charge extraction in thick-film active layers. To address the reviewer’s comments, in page 9 of the revised manuscript, we have added the following sentences: “MoPS nanocrystal incorporation elevated hole (μ ) and electron (μ ) mobility in 3 h e both individual and blended films (Supplementary Figs. 9-12; Supplementary Table 3-4), indicating effective promotion of charge transport pathways. In the D18-Cl:L8- BO blend (~100 nm), both μ and μ are enhanced from 1.16 × 10−3 and 1.31 × 10−3 to h e 2.21 × 10−3 and 2.09 × 10−3 cm2 V−1 s−1 upon MoPS incorporation. Notably, when the 3 thickness increases to ~300 nm, the pristine blend suffers a severe mobility reduction (μ = 0.38 × 10−3 and μ = 0.42 × 10−3 cm2 V−1 s−1), whereas the MoPS -modified film h e 3 maintains high and well-balanced mobility (μ = 1.86 × 10−3 and μ = 1.77 × 10−3 cm2 h e V−1 s−1). This thickness-robust and balanced charge transport effectively suppresses space-charge accumulation and recombination losses, enabling efficient charge extraction in thick-film active layers.” [Detailed responses to all other points follow, including PiFM, in situ absorption, and reference updates]."}, {"round": 2, "reviewer_comments": {"reviewer_1": "This article has been thoroughly revised in accordance with the reviewers' comments and suggestions. The structure is now more logical and coherent, and the language expression is significantly more natural and idiomatic. These revisions have greatly enhanced the overall quality of the manuscript. I am very pleased to recommend the publication of this manuscript on Nature Communications.", "reviewer_2": "The arthors have addressed my main concerns in this revised manuscript. I think it should be accepted by Nat. Comm. A couple of minor issues should be fixed. For instance, there lacks unit for JSC,EQE in Table 1; Most figures in the main manuscript are overly crowded. They can choose to move less important information to the SI.", "reviewer_3": "The authors have thoroughly addressed all points raised in my previous review. The amendments have substantially enhanced the manuscript's clarity, rigor, and overall quality. I am fully satisfied with the revised version and endorse its acceptance for publication in Nature Communications without further revision."}, "author_response": "Our response: We sincerely thank the reviewer for the positive feedback and recommendation for publication. We truly appreciate the time and effort spent in reviewing our manuscript, as well as the valuable comments that helped us improve the quality of our work. [Additional responses regarding Table 1 units and figure crowding]."}]

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