The solar energy utilization is the cross-field frontier of physics, energy, and material science et.al. Organic-inorganic hybrid perovskite material takes the highest interest in these two years. Their light-to-power conversion efficiency boosted to 17.9% (verified by authoritative institution). The very recent record is 19.3%, published in Science. The expected efficiency in near future is 25%, the level of monocrystalline silicon cell. In Mesoscopic Optics and Femtosecond Photophysics Group, sponsored by Foundation for Innovative Research Groups of the NSFC, Prof. Lixin Xiao, Rui Zhu, and CAS Academician Qihuang Gong actively carried out studies and achieved significant improvements.

Organic-Inorganic hybrid perovskite photovoltaic materials contain organic and inorganic units connected by ionic bond. They are new type of photovoltaic material with AMX3 crystalline structure. A is the organic ions such as CH3NH3+; M is divalent metal ions with Pb2 + and Sn2+ as representatives; X is halogen anions of Cl-, Br-, or I-. Inorganic units interconnect as a network for carrier transferring. Excellent charge mobility is found in these materials. The organic units stabilize the structure and improve the solubility for easier processing. Compare to other type of solar cells, these mesoscopic structural perovskite photovoltaic cells are of low cost, broadband spectral absorption, high absorption coefficient, and simplicity in processing. These advantages arouse wide concern both in academy and industry.

The studies showed that the crystalline morphology is crucial to photovoltaic properties of these perovskite solar cells. Prof. Lixin Xiao, Zhaoxin Wu (XJTU), CAS Academician Qihuang Gong, and Xun Hou (XJTU) adopt dual-step processing to optimize perovskite film device containing chloride. Comparing to mono-step method, it is easier to control micro morphology of the cell. Further studies investigate the conditions of film making. They achieve enhancement on light absorbing and charge transferring in the devices. These researches result in perovskite solar cells with improved efficiency. The studies were published in Chem. Commun. (2014, 50, 12458) as inner page cover story and Nanoscale (2014, 6, 8171). Stability is also a key issue for their application. They developed and patented a new hydrophobic hole transporting material which can greatly improve the cell’s stability. （Chem. Commun. 2014, 50, 11196）

The research group led by Prof. Rui Zhu and Prof. Qihuang Qong has also achieved progresses in the interface engineering of perovskite solar cells. In conventional perovskite solar cells, compact n-type metal oxide film is always required as a blocking layer on the transparent conducting oxide (TCO) substrate for efficient electron-selective contact. In this work, alkali salt solution was used to modify the TCO surface to achieve the optimized interface energy level alignment, resulting in efficient electron-selective contact. Devices based on the modified ITO surface could achieve a power conversion efficiency exceeding 15%, together with improved device stability under specific conditions. These results imply that interface engineering provides a promising approach to simplify device fabrication for perovskite solar cells. This work will be published on ACS Nano (DIO: 10.1021/nn5029828). The application for the related patent was also submitted.

In these studies, graduate students, Yingzhuang Ma, Lingling Zheng, and Qin Hu devote great efforts and contribute as first author for the papers. Prof. Zhijian Chen, Asso. Prof. Shufeng Wang, Bo Qu et. al are also the participant. The works are supported by NFSC, MOST, State Key laboratory For Artificial Microstructure and Mesoscopic Physics, and 2011 Project.