RESUMO
Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt < 2 V over 10 hours of continuous operation), and high mobility values >1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices.
RESUMO
Optoelectronic devices based on metal halide perovskites, including solar cells and light-emitting diodes, have attracted tremendous research attention globally in the last decade. Due to their potential to achieve high carrier mobilities, organic-inorganic hybrid perovskite materials can enable high-performance, solution-processed field-effect transistors (FETs) for next-generation, low-cost, flexible electronic circuits and displays. However, the performance of perovskite FETs is hampered predominantly by device instabilities, whose origin remains poorly understood. Here, perovskite single-crystal FETs based on methylammonium lead bromide are studied and device instabilities due to electrochemical reactions at the interface between the perovskite and gold source-drain top contacts are investigated. Despite forming the contacts by a gentle, soft lamination method, evidence is found that even at such "ideal" interfaces, a defective, intermixed layer is formed at the interface upon biasing of the device. Using a bottom-contact, bottom-gate architecture, it is shown that it is possible to minimize such a reaction through a chemical modification of the electrodes, and this enables fabrication of perovskite single-crystal FETs with high mobility of up to ≈15 cm2 V-1 s-1 at 80 K. This work addresses one of the key challenges toward the realization of high-performance solution-processed perovskite FETs.
RESUMO
Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS2 ). The devices are capable of detecting photons with energy below the bandgap of MoS2 . Under the illumination of near-infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible-light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 104 -105 A W-1 owing to the photogating effect and charge trapping mechanism. Besides, the phototransistors can detect a weak visible-light signal with effective optical power as low as 17 picowatts (pW). A thermally induced photoresponse mechanism, the bolometric effect, is proposed as the cause of the negative photocurrent in the NIR regime. The thermal energy of the NIR radiation is transferred to the MoS2 crystal lattice, inducing lattice heating and resistance increase. This model is experimentally confirmed by low-temperature electrical measurements. The bolometric coefficient calculated from the measured transport current change with temperature is -33 nA K-1 . These findings offer a new approach to develop sub-bandgap photodetectors and other novel optoelectronic devices based on 2D layered materials.
