Yan He and Chen Shangshang in Nature Communications: Fullerene-Host Polymers Enhance the Mechanical Stability of Photovoltaic Devices, Achieving Over 18% Efficiency in All-Polymer Solar Cells

Organic solar cells have garnered extensive attention from the research community in recent years due to their lightweight, transparent, flexible, and easily processable characteristics. Currently, polymer–donor–based and small-molecule–acceptor–based solar cells have achieved power conversion efficiencies exceeding 19%, approaching the threshold for commercialization. Fullerene acceptors typically exhibit excellent electron-transport properties and can serve as guest components in ternary organic solar cells to enhance charge extraction and photovoltaic efficiency. However, conventional fullerene small molecules often suffer from undesirable phase separation and dimerization, which degrade device performance and stability and thereby limit their application in organic solar cells.

Recently, Research Groups of He Yan at the Hong Kong University of Science and Technology and Shangshang Chen at Nanjing University This report describes a polyfullerene acceptor, PFBO-C12, which, when incorporated as an acceptor component into all-polymer solar cell architectures, boosts the power conversion efficiency from 16.9% in binary devices to 18.0% in ternary devices. Ultrafast spectroscopy and photophysical studies reveal that PFBO-C12 facilitates hole transport while suppressing charge recombination. Morphological analysis shows that the ternary blend exhibits higher crystallinity and smaller phase-separation domains. Moreover, the introduction of PFBO-C12 reduces voltage losses, endowing all-polymer solar cells with outstanding photostability and mechanical durability in flexible-device applications. These findings demonstrate that incorporating polyfullerenes as acceptor components is an effective strategy for realizing high-efficiency, stable all-polymer solar cells.

First, the authors synthesized a para-xylylene-linked polyfullerene material, PFBO-C12, using a previously reported ATRP polymerization method. Compared with conventional PCBM synthesis, this approach eliminates the need for complex column chromatographic separation and purification, requiring only Soxhlet extraction for purification. This significantly improves fullerene utilization and reduces synthesis costs. Electrochemical tests (CV, Fig. 1b) show that its electrochemical energy levels are comparable to those of PCBM. UV–Vis spectroscopy (Fig. 1c) indicates that, like PCBM, PFBO-C12 can form efficient bulk heterojunctions with the polymer donor (PM6) and the polymer acceptor (PY-V- gamma ) resulting in complementary spectral absorption. Meanwhile, the absorption spectra of the blend films indicate that the incorporation of both PCBM and PFBO-C12 enhances the absorption intensity of the acceptor component (Fig. 1d). Notably, the ternary blend film based on PFBO-C12 exhibits a slightly stronger response in the 300–500 nm wavelength range, which is conducive to photon harvesting and photocurrent generation.

Figure 1. This paper discusses the molecular structure, electrochemical energy level diagram, and UV–vis spectra (pure phase c, mixed phase d).

Therefore, based on PM6: PY-V- gamma : The PFBO-C12-based photovoltaic device achieves an energy conversion efficiency of 18.0%, which is among the highest efficiencies reported to date for all-polymer solar cells (Fig. 2a–c). The incorporation of polyfullerene effectively suppresses charge recombination and enhances carrier mobility in the photovoltaic device (Fig. 2d–e). Compared with binary all-polymer systems, the short-circuit current is increased ( J _SC ) Thanks to the aforementioned improvements in spectral properties, the substantial enhancement in fill factor (FF) is primarily attributable to more optimized morphological features. Morphological studies on crystallinity and phase separation also reveal trends consistent with the photovoltaic performance: the blend film based on PFBO-C12 exhibits enhanced out-of-plane diffraction intensity (Fig. 3b) and suppressed phase-separation domain sizes (Fig. 3d).

Figure 2. Photovoltaic device efficiency characterization results; charge collection and recombination, carrier mobility results

Figure 3. Characterization Results of Crystallinity and Phase Separation (GIWAXS & GISAXS)

Furthermore, based on the aforementioned experiments, the authors conducted a systematic photophysical characterization of three material systems (Figure 4). Transient absorption measurements revealed charge-transfer dynamics consistent with the previous findings: in the ternary system, both PCBM and PFBO-C12 facilitate exciton diffusion and dissociation; moreover, regardless of whether excitation occurs at long or short wavelengths, the PFBO-C12-based ternary system exhibits the fastest hole- and electron-transfer times.

Figure 4. Transient Absorption Experimental Results

Finally, the authors characterized the stability of the device. The results demonstrate that the introduction of PFBO-C12 endows all-polymer solar cells with outstanding photostability and mechanical durability in flexible devices. Moreover, the devices exhibit sufficiently good flexibility in bending tests.

Figure 5 . Characterization of the optical and mechanical stability of the device