Photo-switchable organic field-effect transistors (OFETs) represent an important platform for designing memory devices for a diverse array of products including security (brand-protection, copy-protection, keyless entry, etc.), credit cards, tickets, and multiple wearable organic electronics applications. Herein, we present a new concept by introducing self-assembled monolayers of donor–acceptor porphyrin–fullerene dyads as light-responsive triggers modulating the electrical characteristics of OFETs and thus pave the way to the development of advanced nonvolatile optical memory. The devices demonstrated wide memory windows, high programming speeds, and long retention times. Furthermore, we show a remarkable effect of the orientation of the fullerene–polymer dyads at the dielectric/semiconductor interface on the device behavior. In particular, the dyads anchored to the dielectric by the porphyrin part induced a reversible photoelectrical switching of OFETs, which is characteristic of flash memory elements. On the contrary, the devices utilizing the dyad anchored by the fullerene moiety demonstrated irreversible switching, thus operating as read-only memory (ROM). A mechanism explaining this behavior is proposed using theoretical DFT calculations. The results suggest the possibility of revisiting hundreds of known donor–acceptor dyads designed previously for artificial photosynthesis or other purposes as versatile optical triggers in advanced OFET-based multibit memory devices for emerging electronic applications.

Herein, we report the nanoscale visualization of the photochemical degradation dynamics of MAPbI3 (MA = CH3NH3 +) using infrared scattering scanning near-field microscopy (IR s-SNOM) combined with a series of complementary analytical techniques such as UV–vis and FTIR-spectroscopy, XRD, and XPS. Light exposure of the MAPbI3 films resulted in a gradual loss of MA+ cations starting from the grain boundaries at the film surface and slowly progressing toward the center of the grains and deeper into the bulk perovskite phase. The binary lead iodide PbI2 was found to be the major perovskite photochemical degradation product under the experimental conditions used. Interestingly, the formation of the PbI2 skin over the perovskite grains resulted in a largely enhanced photoluminescence, which resembles the effects observed for core–shell quantum dots. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved degradation dynamics of perovskite absorbers and revealing the associated material aging pathways.

High-efficiency n–i–p perovskite solar cells generally incorporate organic hole-transport layer materials such as spiro-OMeTAD or PTAA, which have intrinsically low charge carrier mobility and therefore require doping to improve transport properties. However, using dopants is known to affect badly the operational stability of perovskite solar cells. Therefore, the development of suitable dopant-free hole-transport materials is the critical issue for realizing perovskite solar cells with high efficiency and long operational lifetimes. Herein, a series of small molecules with triazatruxene, benzodithiophene, triphenylamine, and dithienosilole electron donor core units were designed and explored as solution-processed dopant-free hole-transport materials for perovskite solar cells. The best performance has been obtained using the triazatruxene-based molecule TAT-2T-CNA with terminal alkyl cyanoacetate groups and a 2,2′-bithiophene π-conjugated bridge, which has enabled device efficiency of 20.1% with negligible hysteresis, along with a substantially improved V OC and FF values as compared to the reference devices assembled with PTA as a hole-transport material. The superior performance of TAT-2T-CNA is attributed to the optimal optoelectronic properties of this material and, most importantly, defectless film morphology. Using scanning near-field infrared microscopy (IR-SNOM) technique was shown to be particularly useful for the detection and visualization of defects in thin films of hole-transport materials, which strongly correlate with the device performance. The results obtained in this work are expected to provide new insights facilitating the rational design of efficient dopant-free hole-transport materials for efficient and stable perovskite solar cells.

Herein, we show that thin films of MAPbI 3 , FAPbI 3 , (CsMA)PbI 3 , and (CsMAFA)PbI 3 , where MA and FA are methylammonium and formamidinium cations, respectively, tolerate ultrahigh doses of γ rays approaching 10 MGy without significant changes in their absorption spectra. However, among the studied materials, FAPbI 3 was the only one that did not form metallic lead due to its extreme radiation hardness. Infrared nearfield optical microscopy revealed the radiation-induced depletion of organic cations from the grains of MAPbI 3 and their accumulation at the grain boundaries, whereas FAPbI 3 on the contrary lost FA cations from the grain boundaries. The multication (CsMAFA)PbI 3 perovskite underwent a facile phase segregation to domains enriched with MA and FA cations, which is a principally new radiation-induced degradation pathway. Our findings suggest that the radiation hardness of the rationally designed perovskite semiconductors could go far beyond the impressive threshold of 10 MGy we set herein for FAPbI 3 films, which opens many exciting opportunities for practical implementation of these materials.

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