However, the intrinsic environmental instability of 3D PSCs become a big obstacle to future commercialization. Emerging 2D Ruddlesden-Popper (RP) perovskites with the general formulate of A 2 B n−1 Pb n I 3n+1 , where A is the bulky large cations (e.g., n-butylamine (BA), phenylethlammonium (PEA)), B is the small organic cations (e.g., methylammonium (MA)), and n is the number of confined lead halide octahedral, have recently shown the excellent inherent environmental stability. [5,6] In 2D RP perovskite, the hydrophobic PEA or BA bulky cations prevent the inorganic perovskite layers from oxygen and moisture corrosion, leading to long-term environmental stability. On the other hand, the bulky space cations can passivate the defects and increase the ion migration activation energy in 2D RP perovskite, contributing to the improvement of the thermal stability and photostability.Despite of the impressive stability, the photovoltaic performance of 2D RP PSCs is still lower as compared to their 3D counterparts. [6][7][8] The lower efficiency is ascribed to two major reasons. First, owing to the quantum confinement effect, the enlarged energy bandgap of 2D RP perovskite causes the insufficient light absorption especially at the near-infrared region, leading to the reduced short circuit current (J sc ). Second, 2D RP perovskite crystals prefer growing along the in-plane direction with respect to the substrate. Consequently, the insulating interlayer bulky cations of 2D perovskite impede the out-ofplane charge transfer between the conducting inorganic slabs, leading to insufficient interlayer charge transport. In principle, this poor charge transport capability can be improved by tuning the crystal orientation of 2D RP perovskite. Different strategies including processing, [7,9] solvent, [10] additives, [11,12] and cations engineering [13][14][15][16][17] have been proposed to control crystallographic orientation from the parallel to the vertical direction, and consequently improve the device efficiency. For example, Nie and co-workers first reported the hot-casting method to achieve over 12% efficiency from the 2D perovskite (BA 2 MA 3 Pb 4 I 13 ). [7] Zhao and co-workers developed a slow postannealing process to align the multiphases growth along the vertical direction to the substrate, and obtained a champion PCE of 17.26% for BA 2 MA 3 Pb 4 I 13 2D PSCs. [18] Chen and co-workers, reported the addition of ammonium thiocyanate (NH 4 SCN) can promote vertically oriented crystal growth, leading to the improvement of efficiency and lifetime. [11] Besides, cation engineering is another effective approach to improve the efficiency of 2D PSCs. Liu and co-workers reported a new type of 2D perovskite withOwing 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 li...

Efficient and spectrally stable pure-red perovskite light-emitting diodes (PeLEDs) are still rare and urgently needed for high-definition display. The traditional color tuning method by varying halide composition undergoes phase segregation and has spectral instability issues. Instead of halide mixing, we fabricate pure-red PeLEDs based on quasi-two-dimensional (quasi-2D) perovskites by simultaneously incorporating phenethylammonium (PEA) and 1-naphthylmethylammonium (NMA) cations. The control of PEA and NMA cospacer ratio modulates the phase distribution and the resulting different color emission. The PeLEDs with PEA:NMA molar ratio of 5:5 exhibit a pure-red (635 nm) electroluminescence (EL) with a CIE coordinate (0.709, 0.285) approaching the Rec. 2020 specification. Meanwhile, the optimized devices exhibit an external quantum efficiency (EQE) of 12.41% and a maximum brightness of 1452.6 cd m–2, which are among the best-performing pure-red PeLEDs based on quasi-2D perovskite to date. Additionally, our PeLEDs demonstrate stable EL spectra under different operating voltages and continuous operation.

Stretchable organic solar cells (OSCs) simultaneously possessing high-efficiency and robust mechanical properties are ideal power generators for the emerging wearable and portable electronics. Herein, after incorporating a low amount of trimethylsiloxy terminated polydimethylsiloxane (PDMS) additive, the intrinsic stretchability of PTB7-Th:IEICO-4F bulk heterojunction (BHJ) film is greatly improved from 5% to 20% strain without sacrificing the photovoltaic performance. The intimate multi-layers stacking of OSCs is also realized with the transfer printing method assisted by electrical adhesive "glue" D-Sorbitol. The resultant devices with 84% electrode transmittance exhibit a remarkable power conversion efficiency (PCE) of 10.1%, which is among the highest efficiency for intrinsically stretchable OSCs to date. The stretchable OSCs also demonstrate the ultra-flexibility, stretchability, and mechanical robustness, which keep the PCE almost unchanged at small bending radium of 2 mm for 300 times bending cycles and retain 86.7% PCE under tensile strain as large as 20% for the devices with 70% electrode transmittance. The results provide a universal method to fabricate highly efficient intrinsically stretchable OSCs.