1. Photovoltaic Materials
Accelerated Stability Study of Methylammonium Lead Trihalide Perovskite
Photovoltaic Materials
Ravi K. Misra,*a Sigalit Aharon,b Baili Li,a Iris Visoly- Fisher,a,c Lioz Etgar,b and Eugene A. Katz, a,c
a. Dept. of Solar Energy and Environmental Physics, The Jacob Blaustein Institute for Desert Research (BIDR), Ben-GurionUniversity of the Negev, Sede Boker Campus 84990, Israel,
b. The Institute of Chemistry, The Hebrew University of Jerusalem, Israel
c. The Ilse katz Institute for Nanoscale Science & Technology, Ben Gurion University of the Negev, Beersheva 84105, Israel
Motivation:
Power conversion efficiency of hybrid inorganic-organic metal halide perovskite-based photovoltaic devices has recently reached ~18% [1,2].A significant challenge facing the development of such cells is combining high efficiency and operational stability. However, the published data about degradation mechanisms and stability of perovskite-based materials and photovoltaic devices is very limited. Here we report first results of accelerated stability testing of encapsulated films of methyl ammonium lead trihalide (MAPbX3, X=Br, I) perovskites under concentrated sunlight. The degradation path of the material under concentrated sunlight at different sample temperatures was followed using UV-Vis absorption spectra and X-ray diffraction patterns.
Experimental:
MAPbI3 (cont.)
Normalized XRD patterns of as-grown MAPbI3 film (a); after exposure to 100 suns at sample temperature of 45-55oC (b); pristine PbI2 powder (c).
MAPbBr3 and MAPbI3 films were fabricated on clean glass slides using two-step deposition method followed by encapsulation [3].
Sunlight collected and concentrated outdoors was focused into a transmissive optical fiber and delivered indoors onto the sample [4].
Samples were thermally bonded to the top of a thermoelectric temperature controller, set at 5oC or 25 oC.
As control experiments, samples were annealed in the dark at 35oC, 55oC or 75oC for one hour.
Appearance of a prominent peak attributed to the 001 plane at 12.6o of hexagonal PbI2 (and other characteristic peaks of PbI2 for 002, 003 and 004 planes) indicates degradation of MAPbI3 to PbI2.
MAPbBr3
UV-Vis absorption spectra of a MAPbBr3 film exposed to 100 suns for various times at a sample temperature of ~45-55oC.
Results and Discussion:
The onset at ~540 nm corresponds to the optical band gap of MAPbBr3, Eg~2.3 eV.
No photobleaching observed
A similar behavior was observed for MAPbBr3 films similarly exposed at sample temperature of 25oC.
MAPbI3
(a)
(b)
Conclusions:
1. Photobleaching of MAPbI3 films was observed after their exposure to 100 suns for 60 minutes at elevated sample temperature (~ 45-55oC) due to decomposition of the hybrid perovskite material and crystallization of its inorganic component PbI2.
2. No degradation was observed after MAPbI3 film exposure to the same light intensity and dose but at lower sample temperatures (~25oC).
3. Since MAPbI3 films showed a slight gradual increase in absorption with increasing annealing temperature in the dark, the observed degradation is induced by a combined effect of light and heat during concentrated sunlight exposure.
4. Better stability of MAPbBr3 films was demonstrated, where no photobleaching was observed after exposure of these films to similar stress conditions.
UV-Vis absorption spectra of MAPbI3 film exposed to 100 suns for various times with the thermoelectric platform set to 5oC (a) and 25oC (b). Estimated temperatures of the perovskite film were ~25oC (a) and 45-55oC (b) [5]. (c) MAPbI3 film before and after the annealing for one hour in the dark at 35, 55 and 75oC. The inset shows the normalized number of absorbed solar photons (ASP) from the AM1.5G spectrum as a function of the exposure time.
(c)
Acknowledgements:
R.K.M., E.A.K, I.V.F. acknowledge the support of the European Commission’s StableNextSol COST Action MP1307. R.K.M. is also thankful to Blaustein Center for Scientific Cooperation (BCSC) for providing Postdoctoral Fellowship. L.E acknowledge the Israel Alternative Energy Foundation (I-SAEF) that financed this research, the Ministry of Industry Trade and Labor Office of the Chief Scientist Kamin project No.50303, and the Tashtiot project of the Office of the Chief Scientist.
The onset at ~780 nm corresponds to the optical band gap Eg=1.58 eV .
No photobleaching observed under 100 suns at sample temperature of 25oC.
Photobleaching observed under 100 suns at elevated temperatures (45-55oC). The original dark brown color of the film faded to yellow in the illuminated area.
No photobleaching observed after dark annealing. The absorption improvement is attributed to improved crystallization.
References:
1. Service, R. F.; Science 2014, 344, 458. 2.
3. Laban, W. A.; Etgar, L.; Energy & Environ. Sci. 2013, 6, 3249.
4. Tromholt, T.; Katz, E. A.; Hirsch, B.; Vossier A.; Krebs F. C. Appl. Phys. Lett. 2010, 96,
5. Visoly-Fisher, I.; Mescheloff, A.; Gabai, M.; Bounioux, C.; Zeiri, L.; Sansotera, M.;
Goryachev, A. E.; Braun, A.; Galagan, Y.; Katz, E.A. submitted arXiv: [cond- mat.mtrl-sci].