**5.2 Large-area fabrication**

Hybrid perovskite thin crystals are freer of grain boundaries and exhibit better transport properties than those of the polycrystalline candidates, so their large-area fabrication will ensure a promising future. However, the embedding of volatile and vulnerable organic components on fragile inorganic framework makes them difficult to be fabricated with a large area by deposition techniques or solution-based methods [42, 54]. Furthermore, thin crystals were grown directly on conductive substrates like FTO- or ITO-glass [42, 56], and tailored substrates, such as SiO2/ Si [97], which provide in-situ growth for thin crystals and be directly made into devices. Nevertheless, these large-area thin crystals have rough surfaces and a great number of surface defects, and thus their optoelectronic properties remain inferior to the bulk counterparts. Further optimization of growth methods for large-area thin crystals is needed for industry productions in future.

## **5.3 Long-term stability**

Low stability of the current hybrid perovskite crystal devices hinders their broad practical application. Several factors that affect the device stability, like ion migration [107, 108], can cause hysteresis and photo-induced phase separation, and the interaction

**117**

*Single Crystal Hybrid Perovskite Optoelectronics: Progress and Perspectives*

crystals need to be explored further for device applications.

and device engineering in a variety of optoelectronic technologies.

with markedly-enhanced performance.

**Acknowledgements**

between single crystals and their surroundings lies in the degradation of perovskite by humidity and light [109–111]. Therefore, to further enhance the stability of single crystal devices, optimized device structures should be designed to control the ion migrations. Meanwhile, various compositions and interface engineering approaches are also intensively investigated to confront this critical issue. In addition, encapsulation has

The growth of hybrid perovskite crystals adopt heavy metal ions, like lead (Pb) or tin (Sn), and organic functional groups, which can impact both the environment and human health. This critical issue needs to be overcome, aiming for further commercialization. As for the common MAPbI3 perovskite crystal, the Pb-ion is toxic to both the human health and natural environment; while the organic solvents used during the growth process of crystals are also toxic and easily penetrate into the human body [112]. To solve these problems, capsulation and recycling are needed in the use of crystal materials and organic solvents. Furthermore, other alternative metals to Pb, with a lower toxicity, are also being studied, such as bismuth and antimony [113, 114], and thus, the optoelectronic properties of these Pb-free perovskite

More recently, hybrid perovskite crystals, having different dimensional forms: bulk and thin crystals, and micro−/nano-plates, have been widely explored as functional layers for optoelectronic devices owing to their excellent physical

properties combined with the advantage of ease of processing. Although these types of devices are still in the early stages of development, a strong potential for a variety of technological and commercial applications clearly remains. Here, we presented a comprehensive overview of the recent advances in hybrid perovskite crystals with respect to the background knowledge on the optoelectronic properties and charge transport dynamics of crystals, and their applications in the area of optoelectronic devices, and a fundamental understanding of the device performance. We summarized the main growth methods for the bulk crystals and also some modified and optimized approaches to synthesize thin crystals. The detailed discussions are focused on charge transport characteristics, operation mechanisms, and challenges, aiming to provide a critical understanding of further advance in materials design

In conclusion, the research progress achieved to date in the area of perovskite crystal optoelectronic devices, with the emphasis placed on challenges faced by the research community, has been summarized systematically, and finally perspective on the opportunities offered by this emerging family to photoactive materials in practical and commercial technologies is also proposed. Further exploration of high-quality perovskite crystals, combined with an in-depth understandings of working mechanism of devices, indicates a promising future for wide applications

The author acknowledges support from Discovery Early Career Researcher Award (DECRA) (DE180100167) from the Australian Research Council (ARC).

been demonstrated to be a valid method to protect hybrid perovskite devices.

*DOI: http://dx.doi.org/10.5772/intechopen.95046*

**5.4 Health and environmental concerns**

**6. Conclusions**

*Single Crystal Hybrid Perovskite Optoelectronics: Progress and Perspectives DOI: http://dx.doi.org/10.5772/intechopen.95046*

between single crystals and their surroundings lies in the degradation of perovskite by humidity and light [109–111]. Therefore, to further enhance the stability of single crystal devices, optimized device structures should be designed to control the ion migrations. Meanwhile, various compositions and interface engineering approaches are also intensively investigated to confront this critical issue. In addition, encapsulation has been demonstrated to be a valid method to protect hybrid perovskite devices.

#### **5.4 Health and environmental concerns**

The growth of hybrid perovskite crystals adopt heavy metal ions, like lead (Pb) or tin (Sn), and organic functional groups, which can impact both the environment and human health. This critical issue needs to be overcome, aiming for further commercialization. As for the common MAPbI3 perovskite crystal, the Pb-ion is toxic to both the human health and natural environment; while the organic solvents used during the growth process of crystals are also toxic and easily penetrate into the human body [112]. To solve these problems, capsulation and recycling are needed in the use of crystal materials and organic solvents. Furthermore, other alternative metals to Pb, with a lower toxicity, are also being studied, such as bismuth and antimony [113, 114], and thus, the optoelectronic properties of these Pb-free perovskite crystals need to be explored further for device applications.

### **6. Conclusions**

More recently, hybrid perovskite crystals, having different dimensional forms: bulk and thin crystals, and micro−/nano-plates, have been widely explored as functional layers for optoelectronic devices owing to their excellent physical properties combined with the advantage of ease of processing. Although these types of devices are still in the early stages of development, a strong potential for a variety of technological and commercial applications clearly remains. Here, we presented a comprehensive overview of the recent advances in hybrid perovskite crystals with respect to the background knowledge on the optoelectronic properties and charge transport dynamics of crystals, and their applications in the area of optoelectronic devices, and a fundamental understanding of the device performance. We summarized the main growth methods for the bulk crystals and also some modified and optimized approaches to synthesize thin crystals. The detailed discussions are focused on charge transport characteristics, operation mechanisms, and challenges, aiming to provide a critical understanding of further advance in materials design and device engineering in a variety of optoelectronic technologies.

In conclusion, the research progress achieved to date in the area of perovskite crystal optoelectronic devices, with the emphasis placed on challenges faced by the research community, has been summarized systematically, and finally perspective on the opportunities offered by this emerging family to photoactive materials in practical and commercial technologies is also proposed. Further exploration of high-quality perovskite crystals, combined with an in-depth understandings of working mechanism of devices, indicates a promising future for wide applications with markedly-enhanced performance.

#### **Acknowledgements**

The author acknowledges support from Discovery Early Career Researcher Award (DECRA) (DE180100167) from the Australian Research Council (ARC). *Optoelectronics*
