Subtopic 2: Solution Processed Excitonic Solar Cells

具良好穩定性及高結晶性大尺寸晶粒鈣鈦礦薄膜之研發
Highly crystalline large-grain size perovskite thin film crystals with good  stability 

​許建斌及嚴克友教授，香港中文大學，電子工程系
Profs. Jianbin Xu and Keyou Yan, Department of Electronic Engineering, The Chinese University of Hong Kong

(From left) Prof. Keyou Yan, Prof. Jian-Bin Xu, PhD students Tiankai Zhang and Mingzhu Long of the Department of Electronic Engineering, CUHK.
（左起）中大電子工程學系研究團隊 - 嚴克友教授、許建斌教授、博士研究生張天愷及龍明珠。

針對問題 Problem to be solved
鈣鈦礦太陽能電池（Perovskite Solar Cell，PSC）是國際前沿研究課題，於2013年更被《科學》期刊（Science）納入該年《十大科學突破》之列。可是，這種太陽能電池主要由一類相當不穩定的鈣鈦礦所製成，阻礙了它的商業化。
Perovskite solar cell (PSC) is one of the leading frontier research topics worldwide. In 2013, PSC was selected by the Science journal as one of the “Top 10 Breakthroughs of 2013”. The raw material of this kind of solar cells is a particular kind of instable perovskite, which hampered its device fabrication for commercialization.

 大幅度提高鈣鈦礦物料穩定性 Significant improvement of perovskite stability 

香港中文大學（中大）電子工程學系教授許建斌教授、研究助理教授嚴克友教授及其博士研究生龍明珠、張天愷等，成功優化有機無機雜合鈣鈦礦的合成路徑，研發出名為「非化學計量比的酸鹼反應」（NABR）之合成方法，有效提高了MAPbI3鈣鈦礦的穩定性。這項突破性的成果近日在國際知名學術期刊《自然通訊》（Nature Communications）發表。 

 他們系統化地研究了鈣鈦礦的形成、降解和恢復原理，並在此基礎上提出了NABR。用NABR所製成的鈣鈦礦薄膜，在空氣濕度65%的環境下，能夠保持穩定兩個月，比以傳統方法製造的鈣鈦礦薄膜，只能保持約一星期大大提升。這項研究結果，有望研發出高效率、低成本、高穩定的鈣鈦礦太陽能電池；團隊成員並希望未來此技術能應用於另一類鈣鈦礦太陽能電池。 

The CUHK research team, comprised Prof. Jian-Bin Xu, Prof. Keyou Yan, and their PhD students Mingzhu Long and Tiankai Zhang  from the Department of Electronic Engineering successfully established a technique named “non-stoichiometric acid-base reaction (NABR)” to significantly improve the stability of MAPbI3 perovskite thin films through reaction route optimization in organic and inorganic hybrid perovskite. The breakthrough has been published recently in the latest issue of the renowned journal Nature Communications. They systematically investigated the perovskite formation, degradation and recovery and proposed the NABR based on the mechanism investigation. Being an ion crystal, perovskite is subject to instability under environments of high air humidity. The research team discovered that perovskite material prepared through their NABR methodology is stable for two months under a humidity of approximately 65%, whereas perovskites prepared by traditional methods degraded distinctly after one week. The study sheds light on the development of highly efficient PSC with low cost and high stability, which is promising to be applied in the stability enhancement work of another type of perovskite. 

MAPbI3鈣鈦礦太陽能電池的材料結構。Structure of the MAPbI3 perovskites solar cell.

由NABR合成的MAPbI3鈣鈦礦材料，材料穩定性大幅度提高。該材料在空氣濕度65%的環境下，能夠保持穩定兩個月，而傳統方法製造的鈣鈦礦薄膜只能保持約一星期。Perovskite material prepared through the NABR methodology is stable for two months in a humidity of approximately 65%, whereas other perovskites prepared by traditional methods degrade distinctly after one week.

提升鈣鈦礦物料晶粒結構及電池面積 Enhancement perovskite crystal structure and surface area

及後，團隊成功地製備了高結晶性大尺寸晶粒鈣鈦礦薄膜，以及由此製備的高效率鈣鈦礦電池。在鈣鈦礦多晶薄膜的生長過程中，為了達到良好的結晶品質，團隊把成核中心減少，從而減緩晶體生長速度，令晶粒能夠充分生長。由此方法生產的鈣鈦礦材料，由於其大尺寸晶粒和高結晶性，它的濕度和熱穩定性都有了極大的提升。在結晶過程中，該方法同時免除了抗溶劑的使用，有效地簡化了製備過程，提高了電池製備的成功率。此外，該團隊設計了一種氣體反應器，阻止了水對鈣鈦礦結構本身的破壞，減緩了退化過程，從而大幅度地提高了薄膜濕度穩定性（在約65%濕度環境中，其結晶性可維持近兩個月，比以傳統方法生產、只能維持一星期的鈣鈦礦，穩定性大大提升）。

另一方面，雖然目前小面積鈣鈦礦電池（1平方厘米或以下）達到不俗的光電轉換效率，它們如需達到市場應用要求，必須製作成大面積模組（10 x 10cm2或以上）才行。可是由於基板上導電膜的電阻較大，它們一旦做成大面積模組後，效率往往大為降低。上述由中大團隊設計的氣固反應過程和反應器，能夠製備出緻密的大面積鈣鈦礦薄膜（5 × 5 cm2），大大增加了鈣鈦礦電池的面積，向商業化生產所需要求大大邁進一步。同時，此種新的氣固生產技術不但快捷（數秒便可完成），而且能大規模生產出具良好穩定性的鈣鈦礦物料，進一步促進了產品的生產及商業化潛力。本研究成果已分別發表在Wiley旗下期刊《先進能源材料》（Advanced Energy Materials）及著名國際雜誌《納米能源》(Nano Energy) 上。

相關文獻 Related Paper:

• Mingzhu Long, Tiankai Zhang, Yang Chai, Chun-Fai Ng,  Thomas C. W. Mak, Jianbin Xu & Keyou Yan. (2016). Nonstoichiometric acid-base reaction as reliable synthetic route to highly stable CH3NH3PbI3 perovskite film. Nature Communications, 7: 13503. [Link]
• Mingzhu Long*, Tiankai Zhang*, Wangying Xu, Xiaoliang Zeng, Fangyan Xie, Qiang Li, Zefeng Chen,  Fengrui Zhou, Kam Sing Wong, Keyou* Yan & Jianbin Xu*. (2017).  Large-grain formamidinium PbI3-xBrx for high-performance perovskite solar cells via intermediate halide exchange. Advanced Energy Materials, 7(12): 1601882. [Link]
• Mingzhu Long, Tiankai Zhang, Houyu Zhu, Guixia Li, Feng Wang, Wenyue Guo, Yang Chai, Wei Chen, Qiang Li, Kam Sing Wong, Jianbin Xu* & Keyou Yan*. (2017). Textured CH3NH3PbI3 thin film with enhanced stability for high performance perovskite solar cells. Nano Energy, 33: 485 - 96.  [Link]

Project leaflet 研究計劃簡介

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