Effect of nano-nucleation sites assisted crystallization on performance of perovskite photodetector

Abstract

<sec>Photodetector occupies an important position in the sensor family, but most of the photoelectric conversion materials of photodetectors are inorganic semiconductors, such as GaAs, GaN, Ge and Si, these inorganic semiconductors are usually prepared by complicated methods and high cost, and furthermore, they have poor mechanical flexibility. Organic-inorganic hybrid perovskite materials serving as visible-light sensitizers have the advantages of balanced electron and hole mobilities, adjustable bandgaps, high absorption coefficients, low temperature solution preparation, which make the materials a suitable candidate for inorganic semiconductors.</sec><sec>For planar photodetectors, carriers have greater probabilities to be trapped by the defects in the perovskite films, therefore it is important to fabricate a high-quality perovskite film. However, owing to the low formation energy of perovskite crystals, defects prove to occur on the film surface and grain boundaries, which aggravate the performance of perovskite optoelectronic devices. In this work, we introduce a small quantity of graphene oxide nanosheets (GOSs) on bare glass substrate as effective nucleation sites of perovskite crystals. Owing to the extremely low density of GOSs and large exposed glass basement, the GOSs cannot be regarded as an interface layer. The existence of GOSs on smooth substance reduces the perovskite nucleation barrier, leading to a more preferential crystal growth in these locations, and binds tightly with glass substrate, which passivates the defects efficiently. Meanwhile, the element of O in the GOSs can create Pb–O bond with Pb in the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, further improving the crystal of perovskite. On this basis, planner perovskite photodetector with a structure of glass/GOSs/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/MoO<sub>3</sub>/Au is fabricated. By adjusting the concentration of GOSs deionized water dispersion under the same spin-coating condition, the photoelectric conversion performance of perovskite photodetector is enhanced. Under the influence of the optimal concentration of GOSs, photocurrent of the champion photodetector (1.15 × 10<sup>–6</sup> A) is an order of magnitude higher than that of reference device without GOSs modified (3.58 × 10<sup>–7</sup> A) at 3 V bias, leading to a high ON/OFF current ratio of 5.22 × 10<sup>3</sup>. Besides, improved photoresponse speed is also found in the champion device, with a rise time of 9.6 ms and a decay time of 6.6 ms, respectively. The enhanced performance of GOSs modified perovskite photodetector can be attributed to the significantly reduced defects bringing about an enhanced charge separation and collection performance in the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films.</sec><sec>By introducing extremely low quantity GOSs as the effective perovskite crystal nucleation sites, the perovskite crystallization and thin film can be effectively improved, leading to a positive effect on the performance of perovskite photodetector. This method has a certain universality, and therefore it has a reference value for other structures of perovskite photoelectric devices.</sec>