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Researchers confirmed the passivation effect of remnant PbI2 in perovskite solar cells TEXT SIZE: A A A
Date:2016.07.22 Author:XIA Rui Clicks:
Perovskite solar cells (PSCs) with organo-lead halide perovskites as light harvesters is the latest development of thin film solar cells, their certified power conversion efficiency (PCE) has reached 22.1%, which is higher than that of multicrystalline silicon solar cells (21.3%).
The performance of PSCs strongly depends on the quality of perovskite absorber layer including its crystallinity, morphology, and composition. CH3NH3PbI3 (MAPbI3) is one of the most common light harvesters in PSCs, however, when the MAPbI3 film is prepared a certain amount of PbI2 generally remains in it.
Some researchers believe that the remnant PbI2 could play a passivation role to improve the performance of PSCs, but the others have the opposite views. What is the truth?
A recent research on the passivation effect of remnant PbI2 in PSCs gives the answer. It was performed by the research group led by Prof. FANG Xiaodong from Anhui Institute of Optics and Fine Mechanics (AIOFM), Chinese Academy of Sciences (CAS).
Dr. WANG Shimao et al. prepared MAPbI3 films through two-step spin-coating method, and the content and location of the remnant PbI2 were tuned through varying the heating temperatures of PbI2 and MAPbI3 films, respectively. The charge recombination behavior of PSCs and the passivation effect of remnant PbI2 were investigated through electrochemical impedance spectroscopy (EIS, Fig. 1A and B), dark current, and time-resolved fluorescence emission decay (Fig. 1C) measurements. It was found that the charge recombination in PSCs was gradually suppressed, the fluorescence emission lifetime gradually increased with the content of unreacted PbI2 located at TiO2/perovskite interface increasing. Moreover, when decomposed PbI2 remains among the MAPbI3 particles, the charge recombination resistance (Rrec) and fluorescence emission lifetime increased significantly. So far, the passivation effects of the unreacted and decomposed PbI2 in PSCs have been confirmed unquestionably.
This research was published in Nanoscale entitled "Credible evidence for the passivation effect of remnant PbI2 in CH3NH3PbI3 films in improving the performance of perovskite solar cells".
This work was supported by the National Natural Science Foundation of China, the China Postdoctoral Science Foundation, the National Basic Research Program of China, and the Key Laboratory of Novel Thin Film Solar Cells, Chinese Academy of Sciences.
Fig. 1. (A) The representative Nyquist plots of PSCs prepared at different temperatures obtained under the bias voltage of 0.8 V. (B) The variation of recombination resistance (Rrec) with the preparation temperature obtained under the bias voltages of 0.7, 0.8, 0.9 and 1.0 V. (C) Time-resolved fluorescence emission decay spectra and their fits (lines) of the MAPbI3 films prepared at different temperatures.(Image by WANG Shimao)
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