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Developing intrinsically stretchable organic solar cells (OSCs) with excellent mechanical robustness and long-term operation stability is highly demanded for practical applications. Here, the representative PM6/Y6 active layer film, crosslinked by a photo-crosslinkable small molecule 2,6-bis(4-azidobenzylidene)cyclohexanone (BAC) containing azide groups, exhibits a significantly enhanced stretchability of 18% and toughness of 6.94 MJ m

Two-dimensional (2D) materials were widely used in sensing owing to the tunable physical or chemical properties. For years, optical sensing attracted a massive amount of attention on account of high accuracy, high security, non-invasive measurement, and strong anti-interference ability. Among the various optical sensing schemes, multi-wavelength optical sensing (MWOS) is an important branch and widely adopted in optical image, spectroscopy, or bio/chemical research. However, no spectral selectivity, limited working wavelength range, or intrinsic instability makes conventional 2D materials unsuitable for MWOS. A new class of 2D materials, known as MXene, exhibits outstanding electronic, optical, and thermal properties, leading to new applications in optical sensing. In this paper, we propose an integrated photothermal optical sensor (PHOS) using Ti3C2Tx MXene films. Thanks to the inherent spectral dependence of Ti3C2Tx MXene over a broadband range, the proposed PHOS can respond to different wavelengths from visible to short-wavelength infrared. Because of the efficient photothermal conversion, the PHOS has a control efficiency up to 0.19 π · mW−1 · mm−1 under 980-nm laser pumping and shows a higher control efficiency under red light (690 nm) irradiation. The measured response time of the proposed PHOS is 23.4 μs. This paper brings MXene into chip-integrated optical sensing fields for the first time and shows the potential applications.

Polarization-sensitive photodetectors based on anisotropic semiconductors sense both the intensity and polarization state information without extra optical components. Here, a self-powered organic photodetector (OPD) composed of intrinsically stretchable polymer donor PNTB6-Cl and non-fullerene acceptor Y6 is reported. The PNTB6-Cl:Y6 photoactive film accommodates a remarkable 100% strain without fracture, exhibiting a high optical anisotropy of 1.8 after strain alignment. The resulting OPD not only shows an impressive faint-light detection capability (high spectral responsivity of 0.45 A W

Owing to their insufficient light absorption and charge transport, 2D Ruddlesden-Popper (RP) perovskites show relatively low efficiency. In this work, methylammonium (MA), formamidinum (FA), and FA/MA mixed 2D perovskite solar cells (PSCs) are fabricated. Incorporating FA cations extends the absorption range and enhances the light absorption. Optical spectroscopy shows that FA cations substantially increase the portion of 3D-like phase to 2D phases, and X-ray diffraction (XRD) studies reveal that FA-based 2D perovskite possesses an oblique crystal orientation. Nevertheless, the ultrafast interphase charge transfer results in an extremely long carrier-diffusion length (≈1.98 µm). Also, chloride additives effectively suppress the yellow δ-phase formation of pure FA-based 2D PSCs. As a result, both FA/MA mixed and pure FA-based 2D PSCs exhibit a greatly enhanced power conversion efficiency (PCE) over 20%. Specifically, the pure FA-based 2D PSCs achieve a record PCE of 21.07% (certified at 20%), which is the highest efficiency for low-dimensional PSCs (n ≤ 10) reported to date. Importantly, the FA-based 2D PSCs retain 97% of their initial efficiency at 85 °C persistent heating after 1500 h. The results unambiguously demonstrate that pure-FA-based 2D PSCs are promising for achieving comparable efficiency to 3D perovskites, along with a better device stability.

Low-dimensional Ruddlesden-Popper perovskites (RPPs) exhibit excellent stability in comparison with 3D perovskites; however, the relatively low power conversion efficiency (PCE) limits their future application. In this work, a new fluorine-substituted phenylethlammonium (PEA) cation is developed as a spacer to fabricate quasi-2D (4FPEA)2 (MA)4 Pb5 I16 (n = 5) perovskite solar cells. The champion device exhibits a remarkable PCE of 17.3% with a Jsc of 19.00 mA cm-2 , a Voc of 1.16 V, and a fill factor (FF) of 79%, which are among the best results for low-dimensional RPP solar cells (n ≤ 5). The enhanced device performance can be attributed as follows: first, the strong dipole field induced by the 4-fluoro-phenethylammonium (4FPEA) organic spacer facilitates charge dissociation. Second, fluorinated RPP crystals preferentially grow along the vertical direction, and form a phase distribution with the increasing n number from bottom to the top surface, resulting in efficient charge transport. Third, 4FPEA-based RPP films exhibit higher film crystallinity, enlarged grain size, and reduced trap-state density. Lastly, the unsealed fluorinated RPP devices demonstrate superior humidity and thermal stability. Therefore, the fluorination of the long-chain organic cations provides a feasible approach for simultaneously improving the efficiency and stability of low-dimensional RPP solar cells.

Substituting the hydrogen atoms on the conjugated side chain of a wide-bandgap polymer J52 with chlorine atoms can simultaneously increase the Jsc, Voc, and FF of nonfullerene OSCs, leading to an efficiency boost from 3.78 to 11.53%, which is among the highest efficiencies for as-cast OSCs reported to date. To illustrate the impressive 3-fold PCE enhancement, the chlorination effect on the optical properties and energy levels of polymers, film morphology, and underlying charge dynamics is systematically investigated. Grazing incidence wide-angle X-ray scattering studies show that chlorinated J52-2Cl exhibits strong molecule aggregation, the preferred face-on orientation, and enhanced intermolecular π–π interactions, hence increasing the charge carrier mobility by 1 order of magnitude. Moreover, chlorination modifies the miscibility between the donor and acceptor and consequently optimizes the phase separation morphology of J52-2Cl:ITIC blend films. These results highlight chlorination as a promising appro...