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The electro-active third component (BID)-incorporated PM6-B10-based organic solar cell shows a high performance (PCE = 17.2%) and mechanical stretchability (COSavg = 11.4%), outperforming the PM6-based device (PCE = 15.8%, COSavg = 2.0%).

We report a new molecular design of sequentially regular polymerized small-molecule-acceptors containing flexible spacer (FS) units (PYFS-Reg) to achieve all-polymer solar cells with both high-performance and mechanical stretchability.

We develop a series of polymer donors containing carbazole-based units (CBT) to achieve high-performance (PCE of 15.54%) and thermally stable PSCs.

We develop a non-covalently fused ring acceptor, CPDT–ICMe, to achieve P3HT-based organic solar cells with high-performance (8.17%) and excellent thermal stability.

Highly efficient (PCE = 13.1%) and stretchable (strain at PCE80% = 34%) IS-OSCs are developed using a molecular interdiffusion-assisted TPU-PEDOT:PSS bilayers with excellent adhesion properties.

In this study, two wide-bandgap PM7 polymer derivatives are developed via simple structural modification of the fused-accepting unit by incorporating ester groups on terthiophene at different positions (i.e., two ester groups on the outer thiophenes (PM7 D1) and on the central thiophene (PM7 D2)). This simple modification creates a higher-energy light absorption window, providing better complementary light harvesting with naphthalenediimide-based acceptor, P(NDI2HD-Se). As a result, PM7 D1-based all-polymer solar cells (all-PSCs) exhibit a high power conversion efficiency (PCE) of 9.13%, which outperforms that of the PM7-based all-PSC (PCE = 6.93%). Importantly, the ester structural modification has significant impact on the thin-film mechanical ductility and robustness. For example, elongation properties of PM7 D1 and PM7 D2 pristine films are significantly improved by ca. 2.5 times compared to that of PM7. This result is attributed to the flexible ester groups, which are able to effectively compensate for applied stress. The improved ductile properties of PM7 D1 and PM7 D2 also affect the mechanical ductility of the blend films, leading to 1.5-fold increase in crack onset strain compared with that of the PM7 blend film. Therefore, we demonstrate that the introduction of ester groups in conjugated polymers provides a simple and promising strategy for future stretchable electronics.

The selection of interfacial layers in organic solar cells (OSCs) is crucial for enhancing their power conversion efficiency (PCE) and operational stability. PEDOT:PSS is the most widely used hole transport layer (HTL) for high-performance OSCs; however, device stability is often severely degraded, owing to the strong acidity and hygroscopicity of PEDOT:PSS. Herein, we report a new efficient HTL system comprising an oligo(aniline) host (PBD) and an aryl sulfonic acid dopant (PFBSA), and demonstrate its use in high-performance OSC devices. Desirable properties like solvent orthogonality, high transmittance, excellent conductivity, and appropriate work function establish the suitability of the PBD:PFBSA film as an HTL. Thus, a PBD:PFBSA HTL is employed in the PM6:Y6-based OSC system to achieve a PCE of 15.24%, which is comparable to that of the PEDOT:PSS HTL-based OSC. Importantly, the PBD:PFBSA HTL-based OSC exhibits significantly higher device stability than the PEDOT:PSS HTL. We investigate the film properties of the PBD:PFBSA HTL to elucidate the origin of the superior device stability. Our results highlight the successful design of a protonic acid-doped oligo(aniline)-based material and its practical application as an effective HTL for OSCs.

While the power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been dramatically increased through the development of small molecular acceptors (SMAs), achieving eco-friendly solution processability of OSCs is a crucial prerequisite for their practical application. In this study, we develop three new, green solvent-processable SMAs (YSe–C3, YSe–C6, and YSe–C9) with different outer side-chains (n-propyl (C3), n-hexyl (C6), and n-nonyl (C9)), affording high-performance OSCs with non-halogenated solvent (o-xylene)-processed active layers. Also, the impact of both outer and inner side-chain engineering of these SMAs on the performance of eco-friendly fabricated OSCs is systematically investigated. The outer side-chain structure has a much more significant impact than the inner side-chain. For example, the PM6:YSe–C6 blend affords high-performance OSCs with a power conversion efficiency (PCE) of over 16%, whereas the PCEs of the YSe–C3- and YSe–C9-based OSCs are only 11–14%. The lower PCEs of PM6:YSe–C3 and C9 are mainly attributed to reduced electron mobility and increased charge recombination, resulting from aggregate-containing non-optimal blend morphologies. Interestingly, the well-optimized morphology of the YSe–C6-based blend also affords OSC devices with active layer thickness-independent PCEs, up to a thickness of >400 nm, demonstrating the great potential for large-area device manufacturing via an eco-friendly printing process. Thus, optimizing the outer side-chain structure of Y-series SMAs is essential for producing green solvent-processed high-performance OSCs.

The operation stability of polymer solar cells (PSCs) is one of the most important prerequisites for their practical use. In this work, we report a new acceptor–donor–acceptor (A–D–A) triad-type small molecule, 5TRh-PCBM, as a compatibilizer for enhancing the thermal stabilities and mechanical properties of efficient PSCs while increasing their power conversion efficiencies (PCEs). This multifunctional 5TRh-PCBM molecule, consisting of an oligothiophene segment as the central core and fullerene derivatives as the end groups, is designed to enable strong interactions between the 5TRh-core with various types of efficient polymer donors containing thiophene or fused-thiophene units, while the end fullerene groups preferentially interact with PCBM acceptors. To examine the effectiveness of this molecular compatibilizer, PSCs with different donors (PTB7-Th, PBDB-T, and P3HT) have been fabricated and tested, with addition of various amounts of 5TRh-PCBM. The addition of 5 and 10 wt% of 5TRh-PCBM significantly enhances the thermal and mechanical stabilities of all tested PSCs. Importantly, unlike typical compatibilizers, the addition of 5TRh-PCBM can increase the PCEs of the PSCs due to its light harvesting capability. In particular, the PCE of PTB7-Th:PCBM-based PSCs is increased from 9.37% to 10.09% with the 5 wt% addition of 5TRh-PCBM. Our comprehensive investigations have revealed the effects of 5TRh-PCBM on the optical, morphological, photovoltaic, and mechanical properties of molecularly engineered PSCs.