Is Excess PbI2 Beneficial for Perovskite Solar Cell Performance?

Fangzhou Liu, Qi Dong, Man Kwong Wong, Aleksandra B. Djurišić, Annie Ng, Zhiwei Ren, Qian Shen, Charles Surya, Wai Kin Chan, Jian Wang, Alan Man Ching Ng, Changzhong Liao, Hangkong Li, Kaimin Shih, Chengrong Wei, Huimin Su, Junfeng Dai

Research output: Journal article publicationJournal articleAcademic researchpeer-review

391 Citations (Scopus)


Unreacted lead iodide is commonly believed to be beneficial to the efficiency of methylammonium lead iodide perovskite based solar cells, since it has been proposed to passivate the defects in perovskite grain boundaries. However, it is shown here that the presence of unreacted PbI2 results in an intrinsic instability of the film under illumination, leading to the film degradation under inert atmosphere and faster degradation upon exposure to illumination and humidity. The perovskite films without lead iodide have improved stability, but lower efficiency due to inferior film morphology (smaller grain size, the presence of pinholes). Optimization of the deposition process resulted in PbI2-free perovskite films giving comparable efficiency to those with excess PbI2 (14.2 ± 1.3% compared to 15.1 ± 0.9%) Thus, optimization of the deposition process for PbI2-free films leads to dense, pinhole-free, large grain size perovskite films which result in cells with high efficiency without detrimental effects on the film photostability caused by excess PbI2. However, it should be noted that for encapsulated devices illuminated through the substrate (fluorine-doped tin oxide glass, TiO2 film), film photostability is not a key factor in the device degradation.

Original languageEnglish
Article number1502206
JournalAdvanced Energy Materials
Issue number7
Publication statusPublished - 6 Apr 2016


  • organometallic halide perovskite
  • solar cells
  • stability
  • XRD

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Materials Science


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