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Herein, the impact of thin layer of polyphosphazene derivatives, as a buffer layer between the electron‐transporting layer and the back metal‐contact in mixed‐cation mixed‐halide perovskite solar cells (PSCs), is explored. PSCs with a poly[bis(allylamino)phosphazene] (PPz) interlayer exhibit enhanced rectification in the photo‐induced current density–voltage (J–V) curves, which show improved photovoltaic performance and photostability with reduced hysteresis. The thickness of the interlayer is optimized and the optimized PSCs with PPz buffer layer shows an average open‐circuit voltage (VOC) of ≈1.05 V, a short‐circuit current density (JSC) of around 23.5 mA cm−2, a fill factor of ≈72%, and a power conversion efficiency of about 17.3% for the forward and reverse scans under simulated AM1.5G illumination. Moreover, the application of PPz as an electron‐transporting interlayer in organic solar cells reveals that PPz interfacial layer improves the electron extraction at the cathode. The merit of applying PPz interlayer extends to the possibility of using different metals (such as aluminum, gold, copper, and silver) as the top contact in the prepared PCSs. In general, these experiments reveal a very promising approach to tackle the issue of interfacing, and to improve the performance and stability of PSCs. [ABSTRACT FROM AUTHOR]

Indigoidine is a blue natural pigment, which can be efficiently synthetized in E. coli. In addition to its antioxidant and antimicrobial activities indigoidine due to its stability and deep blue color can find an application as an industrial, environmentally friendly dye. Moreover, similarly to its counterpart regular indigo dye, due to its molecular structure, indigoidine is an organic semiconductor. Fully conjugated aromatic moiety and intermolecular hydrogen bonding of indigoidine result in an unusually narrow bandgap for such a small molecule. This, in its turn, result is tight molecular packing in the solid state and opens a path for a wide range of application in organic and bio-electronics, such as electrochemical and field effect transistors, organic solar cells, light and bio-sensors etc. • Indigoidine a natural pigment synthetized in E. coli. • Fully conjugated aromatic moiety results in a narrow bandgap of 1.3 eV in thin films. • Indigoidine has unusually low LUMO of −4.3 eV. • In OFETs indigoidine shows ambipolar behavior. [ABSTRACT FROM AUTHOR]