JAIST Repository
https://dspace.jaist.ac.jp/Title

Carrier lifetime measurement of perovskite films bydifferential microwave photoconductivity decay

Author(s)Ohdaira, Keisuke; Huynh, Thi Cam Tu; Shimazaki,Ai; Kaneko, Ryuji; Sumai, Yuka; Shahiduzzaman,Md.; Taima, Tetsuya; Wakamiya, Atsushi

Citation

Japanese Journal of Applied Physics, 61(6): 68001

Issue Date2022-05-19

TypeJournal Article

Text version

author

URL

http://hdl.handle.net/10119/18872

RightsThis is the author's version of the work. It is posted
here by permission of The Japan Society of AppliedPhysics. Copyright (c) 2022 The Japan Society ofApplied Physics. Keisuke Ohdaira, Huynh Thi CamTu, Ai Shimazaki, Ryuji Kaneko, Yuka Sumai, Md.
Shahiduzzaman, Tetsuya Taima, and AtsushiWakamiya, Japanese Journal of Applied Physics, 61(6), 2022, 068001. https://doi.org/10.35848/13474065/ac5d22

Description

Japan Advanced Institute of Science and Technology

Carrier lifetime measurement of perovskite films by differential microwave
photoconductivity decay

Keisuke Ohdaira1, Huynh Thi Cam Tu1, Ai Shimazaki2, Ryuji Kaneko2, Yuka Sumai3, Md.
Shahiduzzaman3, Tetsuya Taima3, and Atsushi Wakamiya2

1

Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292, Japan

2

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

3

Nanomaterials Research Institute, Kanazawa University, Kakuma, Kanazawa, Ishikawa

920-1192, Japan

We measure the minority carrier lifetime of perovskite films by differential microwave
photoconductivity decay (µ-PCD). Clear decay curves can be detected from bare andlaminated methylammonium lead iodide (MAPbI3) films by the differential µ-PCD. The
degradation of the bare and laminated MAPbI3 films under air exposure at room
temperature is clearly observed as the continuous change of the decay curves. The
differential µ-PCD can thus be a quick and non-destructive method for thecharacterization of the electrical quality of perovskite films and modules.

1

In recent years, new-type thin-film solar cells with an absorber consisting of
perovskite crystal, so-called perovskite solar cells, have attracted much attention becauseof their superior conversion efficiency.1–17) The photovoltaic (PV) application of theperovskite films is not limited to single-layered cells but also to tandem cells withconventional materials. In particular, perovskite/silicon (Si) tandem solar cells have been
expected as next-generation high-efficiency cells since the fabrication process of
crystalline Si solar cells has been highly matured and the current PV market share has
been dominated almost completely by Si wafer-based solar cells.18–23) In the perovskite/Si
tandem solar cells, their module structures must be similar to those of conventional
crystalline Si PV modules since a perovskite top cell will be formed on a Si wafer-based
bottom cell. The lamination process for the conventional crystalline Si PV modules isperformed typically at 100–150 °C, at which some of perovskite materials, such as
methylammonium lead iodide (MAPbI3), can be thermally degraded.24–26) The
degradation of the perovskite films during and after the lamination process should thus
be readily evaluated for the selection of encapsulant materials and for the optimization oflamination conditions.
Microwave photoconductivity decay (µ-PCD) has been widely used as a conventional,non-contact, and non-destructive method for the evaluation of the minority carrier
lifetime of Si wafers.27–31) A pulse light irradiation generates excess carriers in an absorber,
which enhances the reflection of microwave. The recombination of the excess carriers
results in the decrease of microwave reflection, and a carrier lifetime can be evaluatedfrom the decay of the microwave reflection. µ-PCD is applicable not only for bare Si
wafers but for laminated Si wafers and cells.30,31) Furthermore, µ-PCD can be used also
for the characterization of thin films by using a high-sensitivity system—differential µ2

PCD.28,29) In the differential µ-PCD, microwave reflections are measured at twoneighboring positions with and without excess carrier excitation, resulting in higher
sensitivity by taking the difference of microwave reflection intensity at the two positions.
This technique is expected to be utilized for the evaluation of perovskite films; however,to the best of our knowledge, there has been little work for the µ-PCD measurement ofperovskite films, although similar technique has been already proposed.32,33) This might
be due to the existence of already well-known time-resolved photoluminescence (TRPL).
The demonstration of evaluating laminated perovskite films by differential µ-PCD will
also lead to the future evaluation of laminated perovskite single cells and perovskite/Si
tandem cells. In this note, we report the results on the differential µ-PCD measurementfor MAPbI3 films for the carrier lifetime measurement. The minority carrier lifetimes ofboth bare and laminated films are evaluated by differential µ-PCD.
We prepared 400-nm-thick MAPbI3 films directly on glass substrates with a size of
26×28×0.7 (t) mm. MAPbI3 solution was first synthesized by dissolving 1 M PbI2 and 1
M CH3NH3I (MAI) in DMF:DMSO (4:1) mixed solvent and stirring at 70 °C for 60 min,and was then spin-coated on the glass substrates using antisolvent technique withchlorobenzene, followed by heating on a hotplate at 100 °C for 60 min.16,17) SomeMAPbI3 films were then laminated by using a module laminator (NPC, LM-50X50-S) toform

small-sized

glass-glass

modulesconsistingof3.2-mm-thickcoverglass/thermoplastic polyolefin elastomer (TPO) encapsulant/MAPbI3 sample/TPO
encapsulant/cover glass. The TPO encapsulant was highly transparent in an ultraviolet
wavelength region. The lamination was divided into two processes: degassing process byevacuation at 110 °C for 30 min and adhesion process at a pressure of 60 kPa at 110 °Cfor 10 min. The bare and laminated MAPbI3 films were stored in air at room temperature3

in the dark.
The MAPbI3 films before and after air exposure were characterized by differential µPCD (KOBELCO, LTA-1510EP). A LiYF4 third harmonic generation pulse laser with awavelength of 349 nm and a pulse duration of ~30 ns was used for the generation ofexcess carriers in MAPbI3 films. An areal photon density of a laser pulse is ~2×1014 /cm2.
Note that this corresponds to an excess carrier density (Δn) of ~5×1018 /cm3 if all thephotons are absorbed in MAPbI3 and excited carriers are distributed uniformly in a 400nm-thick MAPbI3 film. This assumption is reasonable since the diffusion coefficient ofcarriers in MAPbI3 is 1.35 cm2/s34) and resulting diffusion length is >400 nm for aduration of >1 ns. Microwave with a frequency of 26 GHz was used for the measurement.
The phase of the 26 GHz microwave was tuned so that the intensity of the reflected
microwave was maximized. The tuning of the microwave phase will also contribute to
the cancellation of the influence of bottom silicon when the perovskite/Si tandem
structures are evaluated in the future.
Figure 1 shows a decay curve obtained by differential µ-PCD from an as-preparedbare MAPbI3 film. One can see a first sharp increase in the microwave reflection intensity,indicating the irradiation of pulse light and resulting formation of excess carriers. The
intensity of the microwave reflection then decreases with time by carrier recombination.
The slope of the decay curve, which generally corresponds to a minority carrier lifetime,
is not constant but change with time. It is known that a radiative lifetime (τrad) in MAPbI3
strongly depends on Δn, and τrad is ~10 ns (Δn ~1018 /cm3), ~100 ns (Δn ~1017 /cm3), and~1 µs (Δn ~1016 /cm3).35) Δn can be roughly estimated to be on the order of 1018 /cm3
immediately after the pulse laser irradiation, as mentioned above, and reflected
microwave intensity may be proportional to Δn. Based on this consideration, Δn at each4

time is roughly estimated, which is added to Fig. 1 together with lifetime values estimatedfrom the slopes of the decay curve. The Δn-dependent lifetime values are similar to theτrad values in Ref. 35, and the carrier recombination in the as-prepared MAPbI3 film maybe basically limited by radiative recombination.
Figure 2 shows decay curves obtained by differential µ-PCD from as-prepared bareand laminated MAPbI3 films. The laminated MAPbI3 film also shows a decay curve witha shape similar to that of the bare film. This indicates that the differential µ-PCD
measurement of perovskite films can be performed through module materials such as
cover glass and encapsulant used for crystalline Si PV modules. The intensity of thereflected microwave from the laminated film is smaller than that from the bare film. Thisis partly because of the optical loss of laser pulse light due to reflection and absorption in
the glass/encapsulant stack. We separately estimated the optical loss originating from themodule materials to be ~20%. Another possible reason for the lower signal intensity inthe laminated film is the attenuation of microwave in the glass/encapsulant stack and/orslight thermal degradation of the MAPbI3 film through the lamination process at
110 °C.24–26)
Figure 3 shows the decay curves obtained by differential µ-PCD from bare andlaminated MAPbI3 films for various air exposure durations. The reduction in themicrowave reflection intensity becomes more rapid after longer air exposure, and therapid decays cannot be explained by the radiative recombination. This clearly indicatesthe emergence of Shockley-Read-Hall (SRH) recombination and the degradation ofMAPbI3 films by air exposure.35) It is demonstrated that the degradation of perovskite
films can be evaluated by differential µ-PCD. Note that the laminated film shows slower
degradation than the bare film, which is given by a protection effect of the lamination
5

against air exposure. It should also be emphasized that the degradation is also seen in thelaminated film. This may be due to the invasion of oxygen and/or moisture from theunsealed edges of the module. Note that no significant changes of the slopes by airexposure are seen near the peak of the decays. One possible explanation for thisphenomenon is that radiative recombination is still dominant at a high Δn of 1018 /cm3.35)
Another possible reason is the inaccuracy of the lifetime obtained near the peak of thedecay curve since the pulse duration of ~30 ns used in this study is on the same order ofthe decay.
We finally discuss the advantage of the µ-PCD in the actual industrial application. µPCD has been widely utilized for the characterization of Si wafers and can be used in theprocess line of Si solar cells. Perovskite/Si tandem solar cells and modules will befabricated in the same process lines as conventional Si cells and modules by adding theprocesses for perovskite top cells. By switching a pulse laser with a long wavelength of~900 nm, which is not absorbed in perovskite top cell but absorbed in Si bottom cell, thequality of bottom cells can also be evaluated in the same measurement system. µ-PCD isthus applicable in the production lines of perovskite/Si tandem cells as a quick and nondestructive method to evaluate absorber materials. Another advantage of the usage of µPCD is that it can be a portable system and available outdoors.30) µ-PCD will be utilized
for the evaluation of perovskite/Si PV modules in the large-scale PV power plants or otherinstalled sites. This is an advantage of µ-PCD over TRPL, which is also widely used forthe carrier lifetime measurement of perovskite films.
In conclusion, we investigated the utilization of differential µ-PCD for thecharacterization of perovskite films and its time-dependent degradation by air exposure.
We demonstrated that differential µ-PCD can measure the carrier lifetime of MAPbI3
6

films, even after the module lamination with a structure similar to Si solar cells. The decay
curve changes with air-exposure duration, and reflected microwave signals drop more
rapidly after longer air exposure, which is a clear observation of the degradation ofMAPbI3 films. Slower progression of degradation is confirmed in the laminated MAPbI3films, indicating the protecting effect by the module materials. Differential µ-PCD can bea quick and non-destructive tool for the evaluation of perovskite/Si tandem cells in thecell/module production lines and module-installed sites.
The TPO encapsulant was provided by Dai Nippon Printing Co., Ltd. The authors
would like to thank Mr. Shinichiro Hayashi and Ms. Tomoko Hori of Japan Advanced
Institute of Science and Technology for their supports for the experiments. This work is
supported by the New Energy and Industrial Technology Development Organization(NEDO).

7

References
1) A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, J. Am. Chem. Soc. 131, 6050
(2009).
2) M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami, and H. J. Snaith, Science 338,643 (2012).
3) J. H. Heo, S. H. Im, J. H. Noh, T. N. Mandal, C.-S. Lim, J. A. Chang, Y. H. Lee, H.-j.
Kim, A. Sarkar, and M. K. Nazeeruddin, Nat. Photonics 7, 486 (2013).
4) J.-H. Im, I.-H. Jang, N. Pellet, M. Grätzel, and N.-G. Park, Nat. Nanotechnol. 9, 927(2014).
5) D.-Y. Son, J.-W. Lee, Y. J. Choi, I.-H. Jang, S. Lee, P. J. Yoo, H. Shin, N. Ahn, M.
Choi, D. Kim, and N-.G Park, Nat. Energy 1, 16081 (2016).
6) M. Saliba, T. Matsui, K. Domanski, J.-Y. Seo, A. Ummadisingu, S. M. Zakeeruddin,J.-P. Correa-Baena, W. R. Tress, A. Abate, A. Hagfeldt, and M. Grätzel, Science 354,206 (2016).
7) N. J. Jeon, H. Na, E. H. Jung, T.-Y. Yang, Y. G. Lee, G. Kim, H.-W. Shin, S. I. Seok,J. Lee, and J. Seo, Nat. Energy 3, 682 (2018).
8) W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo, and S. I. Seok, Science348, 1234 (2015).
9) M. Ozaki, Y. Nakaike, A. Shimazaki, M. Jung, N. Maruyama, S. Yakumaru, A. I.
Rafieh, P. Ekanayake, T. Sato, Y. Shimakawa, T. Sasamori, Y. Murata, R. Murdey, andA. Wakamiya, Bull. Chem. Soc. Jpn. 92, 1972 (2019).
10) M. Ozaki, Y. Ishikura, M. A. Truong, J. Liu, I. Okada, T. Tanabe, S. Sekimoto, T.
Ohtsuki, Y. Murata, R. Murdey, and A. Wakamiya, J. Mater. Chem. A 7, 16947 (2019).
11) T. Nakamura, T. Handa, R. Murdey, Y. Kanemitsu, and A. Wakamiya, ACS Appl.
8Electron. Mater. 2, 3794 (2020).
12) Y. Cho, J. Bing, H. D. Kim, Y. Li, J. Zheng, S. Tang, M. A. Green, A. Wakamiya, S.
Huang, H. Ohkita, and A. W. Y. Ho-Baillie, ACS Appl. Mater. Interf. 13, 39178 (2021).
13) Md. Shahiduzzaman, S. Fukaya, E. Y. Muslih, L. Wang, M. Nakano, Md.
Akhtaruzzaman, M. Karakawa, K. Takahashi, J -M. Nunzi, and T. Taima, Materials
13, 2207 (2020).
14) Md. Shahiduzzaman, E. Y. Muslih, A. K. M. Hasan, L. Wang, S. Fukaya, M. Nakano,
M. Karakawa, K. Takahashi, Md. Akhtaruzzaman, J.-M. Nunzi, T. Taima, Chem. Eng.
J. 411, 128461 (2021).
15) Md. Shahiduzzaman, M. I. Hossain, S. Otani, L. Wang, S. Umezu, T. Kaneko, S.
Iwamori, K. Tomita, Y. H. Tsang, Md. Akhtaruzzaman, D. Knipp, J.-M. Nunzi, M.
Isomura, J. A. Zapien, and T. Taima, Chem. Eng. J. 426, 131831 (2021).
16) Md. Shahiduzzaman, D. Kuwahara, M.Nakano, M. Karakawa, K. Takahashi, L. Nunzi,and T. Taima, Nanomaterials 10, 1676 (2020).
17) Md. Shahiduzzaman, A. Kulkarni, S. Visal, L. L. Wang, M. Nakano, M. Karakawa,
K. Takahashi, S. Umezu, A. Masuda, S. Iwamori, M. Isomura, T. Miyasaka, K.Tomita,and T. Taima, Sustain. Energy Fuels 4, 2009 (2020).
18) J. Werner, B. Niesen, and C. Ballif, Adv. Mater. Interf. 5, 1700731 (2018).
19) A. Al-Ashouri, E. Köhnen, B. Li, A. Magomedov, H. Hempel, P. Caprioglio, J. A.
Márquez, A. B. M. Vilches, E. Kasparavicius, J. A. Smith, N. Phung, D. Menzel, M.
Grischek, L. Kegelmann, D. Skroblin, C. Gollwitzer, T. Malinauskas, M. Jošt, G.
Matič, B. Rech, R. Schlatmann, M. Topič, L. Korte, A. Abate, B. Stannowski, D.
Neher, M. Stolterfoht, T. Unold, V. Getautis, and S. Albrecht, Science 370, 1300
(2020).
920) M. Jošt, L. Kegelmann, L. Korte, and S. Albrecht, Adv. Energy Mater. 10, 1904102(2020).
21) D. Yang, X. Zhang, Y. Hou, K. Wang, T. Ye, J. Yoon, C. Wu, M. Sanghadasa, S.
(Frank) Liu, and S. Priya, Nano Energy 84, 105934 (2021).
22) C. Kamaraki, M. T. Klug, T. Green, L. M. Perez, and C. Case, Appl. Phys. Lett. 119,070501 (2021).
23) S. Kim, T. T. Trinh, J. Park, D. P. Pham, S. Lee, H. B. Do, N. N. Dang, V.‑A. Dao, J.
Kim, and J. Yi, Sci. Rep. 11, 15524 (2021).
24) N.-K. Kim, Y. H. Min, S. Noh, E. Cho, G. Jeong, M. Joo, S.-W. Ahn, J. S. Lee, S.
Kim, K. Ihm, H. Ahn, Y. Kang, H.-S. Lee, and D. Kim, Sci. Rep. 7, 4645 (2017).
25) T. T. Ava, A. A. Mamun, S. Marsillac, and G. Namkoong, Appl. Sci. 9, 188 (2019).
26) A. Kumar, U. Bansode, S. Ogale, and A. Rahman, Nanotechnology 31, 365403 (2020).
27) T. Tiedje, J. I. Haberman, R. W. Francis, and A. K. Ghosh, Appl. Phys. Lett. 54, 2499
(1983).
28) H. Hashizume, F. Ojima, K. Iba, N. Yoshida, H. Takamatsu, and S. Sumie, IEICE
Technical Report 97, 29 (1997). (in Japanese)29) K. Ohdaira, H. Takemoto, K. Shiba, and H. Matsumura, Appl. Phys. Express 2,061201 (2009).
30) M. A. Islam, D. C. Nguyen, and Y. Ishikawa, Jpn. J. Appl. Phys. 58, 106507 (2019).
31) N. Nishikawa, S. Yamaguchi, and K. Ohdaira, Microelectron. Reliab. 79, 91 (2017).
32) T. J. Savenije, A. J. Ferguson, N. Kopidakis, and G. Rumbles, J. Phys. Chem. C 117,24085 (2013).
33) T. J. Savenije, D. Guo, V. M. Caselli, and E. M. Hutter, Adv. Energy Mater. 2020,1903788 (2020).
1034) P. Ščajev, S. Miasojedovas, and S. Juršėnas, J. Mater. Chem. C 8, 10290 (2020).
35) F. Staub, U. Rau, and T. Kirchartz, ACS Omega 3, 8009 (2018).

Figure Captions

Fig. 1 Decay curve obtained by differential µ-PCD from an as-prepared bare MAPbI3film. The inset shows the magnified view of the decay curve near the peak.

Fig. 2

Decay curves obtained by differential µ-PCD from as-prepared bare andlaminated MAPbI3 films.

Fig. 3 Decay curves obtained by differential µ-PCD from (a) bare and (b) laminated
MAPbI3 films for various air exposure durations.

11

~20 ns
Δn ~1018 /cm3~700 ns
Δn ~1017 /cm30.10.20.30.40.5Time (μs)~8 μsΔn ~1016 /cm30246Time (μs)
Fig. 1 K. Ohdaira et al.,

12810

Bare

Laminated

0246Time (μs)
Fig. 2 K. Ohdaira et al.,

13810

(a)

00h
20 h
42 h
68 h

246

Microwave intensity (arb. unit)

Time (μs)

Fig. 3 K. Ohdaira et al.,14810