Optical memory devices based on photoswitchable OFETs comprising light sensitive layers of photochromic spiropyran salts revealed advanced electrical characteristics and superior stability.

semiconductor and dielectric. [23][24][25][26][27] The latter approach seems to be the most promising. It is known that the highest density of charge carriers in operating OFET fl ows in a few molecular layers of semiconductor adjacent to dielectric. [ 28 ] Therefore, photoisomerization of a photochromic compound at the dielectric/semiconductor interface changes signifi cantly electrical characteristics of the conducting channel (density of traps/carriers, electrical permittivity, capacitance) and the device itself thus providing the required photoswitching effect.While comparing the characteristics of the OFET-based memory elements, few important parameters should be considered. First of all, it is a switching coeffi cient defi ned as k sw = I DS (1)/ I DS (2), where I DS (1) and I DS (2) correspond to the drain currents of the OFET in states 1 and 2, respectively, measured at the same gate voltage V GS = const, which shows how strong is the hysteresis in the electrical characteristics of the transistor or how wide is the memory window. The device operating voltages, a programming speed, and a long-term stability of the distinct electrical states (retention characteristics) are also crucially important.Analyzing previous reports on the OFET-based optical memories comprising photochromic materials, one can notice their low switching coeffi cients which stay typically below 10 and hardly exceed 100 for the best examples (Table S1, Supporting Information). These devices typically operate at high voltages (30-100 V), while their programming is very slow and requires light illumination within tens of seconds or even minutes. To make this type of memory elements more interesting for practical applications one has to improve signifi cantly their characteristics. We have reported very recently memory elements based on a photochromic spirooxazine which showed decent operating voltages (<5 V) and reasonably high switching coefficients of ≈10 3 . [ 29 ] Unfortunately, the programming speeds were still rather low mainly due to fundamental limitations of the used materials and the device architecture.Here we present a concept of the memory elements operating via optically and electrically triggered charge separation between the organic semiconductor ([60]fullerene) and the photochromic dielectric (specially designed 1,2-bis(hetaryl) ethene) layers. The proposed approach allowed us to decrease the device programming time by three orders of magnitude down to few milliseconds with a high potential to reach practically interesting microsecond operation regime. Additionally, the designed devices showed exceptionally wide memory windows refl ected by the switching coeffi cients of ≈10 5 at reasonably low operation voltages (3-10 V).

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