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We develop a series of poly(triarylamine)-based polymers with hydrophilic OEG side chains. The DEG-PTAA-based perovskite solar cell shows the highest efficiency of 22.26% with superior operational stability to the other devices.

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

New polymer acceptors (PYSiO-X (X = 0–30%)) containing siloxane-based flexible spacers (SiO-FSs) are developed. The resulting halogen-free solvent processed all-polymer solar cells show high photovoltaic efficiency and mechanical robustness.

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.

Organic semiconductor-based optoelectronic devices, such as organic solar cells (OSCs) and organic light-emitting diodes (OLEDs), have been investigated for solution-processable roll-to-roll electronic devices. However, for commercial applications, OSCs and OLEDs require highly efficient device performance and effective fabrication processing methods. To achieve this, this work reports the use of solution-processable quinoxaline–phosphine oxide based small molecules (QPSMs) as electron transport layers (ETLs) in OSCs and OLEDs. QPSMs can be dissolved in alcohol owing to the strong dipole moments within their molecular structures, thereby resulting in simple and effective processing during device fabrication. Moreover, QPSMs improve electron injection/extraction via the well-matched energy levels in both OSCs and OLEDs. In particular, optimized OSCs and OLEDs with ((4-(2,3-diphenylquinoxalin-5-yl)phenyl)diphenylphosphine oxide, QxTPPO1) show power conversion efficiency (PCE) of 16.83% in polymer donor : nonfullerene acceptor systems, PCE of 10.07% in polymer donor : fullerene acceptor systems, and external quantum efficiency of 5.00%, which are enhanced by approximately 23%, 19%, and 12%, respectively, compared to those of the reference devices, thereby exhibiting improved device stability.

While excellent thermal and mechanical stabilities of all-polymer solar cells (all-PSC) have been demonstrated, the storage stability of all-PSCs has rarely been studied. In this paper, the storage stability of all-PSCs is systematically investigated and compared to fullerene-based polymer solar cells (PCBM-PSCs). We identify that the efficient inverted type all-PSCs made with a molybdenum oxide (MoO3) anode interfacial layer exhibit degradation over short periods of storage even under inert nitrogen-filled and dark conditions, while the control inverted PCBM-PSCs containing the same polymer donor are relatively more stable. To elucidate the origin of the poor storage stability, morphological and electrical properties of all-PSCs are investigated. We reveal that the work function of MoO3 is largely changed during the storage because of the interaction between MoO3 and the underneath naphthalene dimide (NDI)-based polymer acceptors (PAs). This causes unfavorable energy-level alignment in devices, resulting in increased charge recombination and deteriorated charge collecting efficiency. To resolve this issue, we propose two effective strategies: (i) introducing a passivation layer to physically separate the NDI-based PAs and MoO3, and (ii) replacing MoO3 with an efficient polymer interlayer. We prove that the modified all-PSCs not only exhibit excellent storage stability with high power conversion efficiency for more than 45 days, but also show high air-stability even without encapsulation. Our findings provide deeper understanding of the storage stability of all-PSCs and suggest future guidelines for efficient and burn-in free all-PSCs.

We report morphological control with phenyl-C60-butyric acid methyl ester (PCBM) molecular aggregation for perovskite–PCBM bulk heterostructure (Pe–PCBM BHS) solar cells. Solar cells prepared via the Pe–PCBM BHS method exhibited a higher power conversion efficiency (PCE) of 18% than 11% from a device with a conventional planar heterojunction structure. The Pe–PCBM BHS can enhance device efficiency by improving electron transfer, shortening the electron transport length required for collection, and reducing the charge transfer resistance at the interface between the perovskite and PCBM through an increase of the perovskite crystal size and construction of a vertical perovskite–PCBM intermixing zone. To the best of our knowledge, the high PCE achieved by our Pe–PCBM BHS is the highest value to be reported in an inverted perovskite solar cell without buffer layers, such as metal oxides or low work function metals.

Controlling the morphological stability of non-fullerene polymer solar cells (NF-PSCs) is a critical process for improving photovoltaic performances. In many systems, liquid additives have been widely used to produce favorable morphological features; however, liquid additives frequently leave residues after thermal treatment owing to their high boiling points, which has detrimental effects on the reproducibility of NF-PSCs. In this study, commercially available and volatilizable solid additives, 9,10-anthracenedione (BDT-1) and benzo[1,2-b:4,5-b′]dithiophene-4,8-dione (BDT-2), are selected to coordinate the molecular arrangement to enhance absorption intensity, charge transfer, and molecular crystallinity. Suppressed bimolecular recombination and a favorable balance between the domain size and relative domain purity were observed with the introduction of both solid additives, which improved the photovoltaic parameters of NF-PSCs. PM6:TPT10-based devices with BDT-1 and BDT-2 additives achieved the best power conversion efficiencies (PCEs) of 16.26% and 15.18%, respectively, which were better than the 13.55% achieved with a 1,8-diiodooctane (DIO) additive. Other NF-PSC systems of PBDB-T:TPT10 and PTQ10:TPT10 blends also showed that the photovoltaic performance with the solid additives is superior to that with liquid additives. These results imply that the use of solid additives is a promising strategy to improve the PCEs of NF-PSCs.