Quasi-2D Organic-Inorganic Metal Halide Perovskites for Photodetectors Application

準二維有機無機雜化鈣鈦礦在光探測器中的應用

Student thesis: Doctoral Thesis

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Award date9 Aug 2019

Abstract

Conventional three-dimensional (3D) organic-inorganic halide perovskites have recently undergone unprecedented rapid development. Yet, their inherent instabilities over moisture, light, and heat remain a crucial challenge prior to the realization of commercialization. By contrast, the emerging quasi-two-dimensional (quasi-2D) Ruddlesden-Popper-type perovskites have recently attracted increasing attention owing to their great environmental stability. However, the research of quasi-2D perovskites is just in their infancy. In this work, we focused on the synthesis, optoelectronic properties of quasi-2D metal halide perovskites, strategies for their device performance improvement and applications of photodetectors.

First, we begin with a brief introduction of the quasi-2D Perovskites, along with a detailed comparison to 3D counterparts. Then, the aims and objectives of the thesis are given.

Second, a discussion of the organic spacer cation engineering of quasi-2D perovskites is presented. We reported the synthesis of a novel series of quasi-2D perovskites based on the general formula (iBA)2(MA)n-1PbnI3n+1 (iBA = iso-butylamine; MA = methylamine), where the relatively pure phase (iBA)2PbI4 and (iBA)2MA3Pb4I13 films can be obtained. Because of the shorter branched-chain of iBA as compared with that of its linear equivalent (n-butylamine, BA), the resulting (iBA)2(MA)n-1PbnI3n+1 perovskites exhibit much enhanced photodetection properties without sacrificing their excellent stability. Through hot-casting, the optimized (iBA)2(MA)n-1PbnI3n+1 perovskite films with n=4 give the significantly improved crystallinity, demonstrating the high responsivity, large on-off ratio and fast response speed. This part of work suggests that more attention should be paid to the intrinsic properties of quasi-2D perovskite films (organic spacer cations) which play a significant role in determining the device performance.

Next, compositional engineering is demonstrated to overcome difficulties in fabricating high-quality perovskite films. We successfully introduced both FA (FA = Formamidinium) and Cs cations into the quasi-2D perovskites (iBA)2(MA)3Pb4I13 to modulate the qualities of thin films as well as improve the performance of devices. When incorporated in typical rigid photodetectors, the resulting FA, Cs-doped (iBA)2(MA)3Pb4I13 perovskites exhibit much enhanced photodetection properties compared with those of pristine (iBA)2(MA)3Pb4I13 under 532 nm illumination. Moreover, once fabricated as flexible photodetectors on polyimide, the FA, Cs-doped quasi-2D perovskites show further improved photodetection performance. This part of work paves a way for future development of high-performance flexible photodetectors for next-generation optoelectronic devices.

Finally, we summarize results presented in this thesis and discuss possible future research directions in related fields. All of these not only provide an insight into the applications of quasi-2D perovskites on photodetector devices, but also exhibit versatile techniques for further performance enhancement of other perovskite optoelectronics.

    Research areas

  • Quasi-2D Perovskites, Thin Films, Spacer Cation, Hot Casting, Mixed Cations Incorporation, Perovskite Photodetectors