1. ACS Appl. Mater. Interfaces | Research Article

Approximately 800-nm-Thick Pinhole-Free Perovskite Films via Facile Solvent Retarding Process for Efficient Planar Solar Cells
Zhongcheng Yuan, Yingguo Yang, Zhongwei Wu, Sai Bai, Weidong Xu, Tao Song, Xingyu Gao, Feng Gao, and Baoquan Sun

ACS Appl. Mater. Interfaces, 2016, 8 (50), pp 34446–34454 dol: 10.1021/acsami.6b12637


Device performance of organometal halide perovskite solar cells significantly depends on the quality and thickness of perovskite absorber films. However, conventional deposition methods often generate pinholes within ∼300 nm-thick perovskite films, which are detrimental to the large area device manufacture. Here we demonstrated a simple solvent retarding process to deposit uniform pinhole free perovskite films with thicknesses up to ∼800 nm. Solvent evaporation during the retarding process facilitated the components separation in the mixed halide perovskite precursors, and hence the final films exhibited pinhole free morphology and large grain sizes. In addition, the increased precursor concentration after solvent-retarding process led to thick perovskite films. Based on the uniform and thick perovskite films prepared by this convenient process, a champion device efficiency up to 16.8% was achieved. We believe that this simple deposition procedure for high quality perovskite films around micrometer thickness has a great potential in the application of large area perovskite solar cells and other optoelectronic devices.

2. Applied Physics Letters | Research Article

Inhomogeneous degradation in metal halide perovskites

Rong Yang, Li Zhang, Yu Cao, Yanfeng Miao, You Ke, Yingqiang Wei, Qiang Guo, Ying Wang, Zhaohua Rong, Nana Wang, Renzhi Li, Jianpu Wang, Wei Huang, and   Feng Gao
Appl. Phys. Lett. 111, 073302 (2017); doi: 10.1063/1.4999630

Although the rapid development of organic-inorganic metal halide perovskite solar cells has led to certified power conversion efficiencies of above 20%, their poor stability remains a major challenge, preventing their practical commercialization. In this paper, we investigate the intrinsic origin of the poor stability in perovskite solar cells by using a confocal fluorescence microscope. We find that the degradation of perovskite films starts from grain boundaries and gradually extend to the center of the grains. Firmly based on our findings, we further demonstrate that the device stability can be significantly enhanced by increasing the grain size of perovskite crystals. Our results have important implications to further enhance the stability of optoelectronic devices based on metal halide perovskites.
3. Nature Communication | Research Article

Wei Zou, Renzhi Li, Shuting Zhang, Yunlong Liu, Nana Wang, Yu Cao, Yanfeng Miao, Mengmeng Xu, Qiang Guo, Dawei Di, Li Zhang, Chang Yi, Feng Gao, Richard H. Friend, Jianpu Wang & Wei Huang

Nature Communications, volume 9, Article number: 608 (2018) doi:10.1038/s41467-018-03049-7

Efficiency roll-off is a major issue for most types of light-emitting diodes (LEDs), and its origins remain controversial. Here we present investigations of the efficiency roll-off in perovskite LEDs based on two-dimensional layered perovskites. By simultaneously measuring electroluminescence and photoluminescence on a working device, supported by transient photoluminescence decay measurements, we conclude that the efficiency roll-off in perovskite LEDs is mainly due to luminescence quenching which is likely caused by non-radiative Auger recombination. This detrimental effect can be suppressed by increasing the width of quantum wells, which can be easily realized in the layered perovskites by tuning the ratio of large and small organic cations in the precursor solution. This approach leads to the realization of a perovskite LED with a record external quantum efficiency of 12.7%, and the efficiency remains to be high, at approximately 10%, under a high current density of 500 mA cm−2.

4. Advanced Materials | Communication

Long Electron–Hole Diffusion Length in High‐Quality Lead‐Free Double Perovskite Films

Weihua Ning  Feng Wang  Bo Wu  Jun Lu  Zhibo Yan  Xianjie Liu  Youtian Tao  JunMing Liu Wei Huang  Mats Fahlman  Lars Hultman  Tze Chien Sum*  Feng Gao*

Advanced Materials,

Developing environmentally friendly perovskites has become important in solving the toxicity issue of lead‐based perovskite solar cells. Here, the first double perovskite (Cs2AgBiBr6) solar cells using the planar structure are demonstrated. The prepared Cs2AgBiBr6 films are composed of high‐crystal‐quality grains with diameters equal to the film thickness, thus minimizing the grain boundary length and the carrier recombination. These high‐quality double perovskite films show long electron–hole diffusion lengths greater than 100 nm, enabling the fabrication of planar structure double perovskite solar cells. The resulting solar cells based on planar TiO2 exhibit an average power conversion efficiency over 1%. This work represents an important step forward toward the realization of environmentally friendly solar cells and also has important implications for the applications of double perovskites in other optoelectronic devices.


Accepted in Advanced Materials, 30 March 2018