· Web viewKey Lab of Artificial Micro- and Nano-Structures of Ministry of Education of China, Department of Electronic Science & Technology, School of Physics and Technology, Wuhan

Supplemental Material

Performance Enhancement of Perovskite Solar Cells with Mg-

doped TiO2 Compact Film as the Hole-blocking Layer

Jing Wang,1 Minchao Qin,1 Hong Tao,1 Weijun Ke,1 Zhao Chen,1 Jiawei Wan,1 Pingli Qin,1 Liangbin Xiong,1,2 Hongwei Lei,1 Huaqing Yu,2 Guojia Fang1,a)

1Key Lab of Artificial Micro- and Nano-Structures of Ministry of Education of China,

Department of Electronic Science & Technology, School of Physics and Technology, Wuhan

University, Wuhan 430072, People’s Republic of China

2School of Physics and Electronic-Information Engineering, Hubei Engineering University,

Xiaogan, 432000, People’s Republic of China

FIG. S1. Hysteresis effect in the J-V curves of perovskite solar cells with the none-doped

TiO2 and the Mg(0.10)-TiO2 compact layer.

Fig. S1 shows hysteresis effect in the photocurrent density-voltage (J-V) curves of

perovskite solar cells with the none-doped TiO2 and the Mg(0.10)-TiO2 compact layer.

Forward scan (from short-circuit to open-circuit) was abbreviated as FS and reverse scan

(from open-circuit to short-circuit) was abbreviated as RS. The scan rate was 10 mV s-1.1, 2

The prominent feature in the photocurrent-voltage (I-V) hysteresis appears near open-circuit

condition, a modified I-V hysteresis factor is given by formula S(1):

, S(1)

where JRS(0.8Voc) is the photocurrent density at 80% of open-circuit voltage (Voc) bias for the

RS, while JFS(0.8Voc) is the photocurrent density for the FS. The hysteresis factor of the

Mg(0.10)-TiO2 cell and the none-doped TiO2 cell are 0.31 and 0.38, respectively. The reason

of the less hysteresis effect of the Mg(0.10)-TiO2 cell could be the better hole-blocking and

electron-collecting ability of the Mg(0.10)-TiO2 film. However, the hysteresis is strongly

dependent on the contact material and the perovskite crystal size.3 In this study, the main

contact material is mesoporous TiO2 layer rather than the compact TiO2 layer, and the

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perovskite of the two kinds of cells were prepared in the same way, so the hysteresis effects

of the two kinds of solar cells did not show significant difference.

3

FIG. S2. SEM-EDX spectrum for Mg(0.10)-TiO2 nanoparticles on FTO glass after sintering

at 500 °C for 2h.

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FIG. S3. XRD patterns for none-doped TiO2 and Mg(0.10)-TiO2 nanoparticles after sintering

at 500 °C; * indicates MgTiO3 phase.

The X-ray diffraction (XRD) patterns (Fig. S3) show the anatase crystal structures of the

samples after annealing at 500°C.4 Two main MgTiO3 phases with ilmenite (ordered

corundum) type structure crystallized after Mg doping which illustrates the existence of

MgTiO3 in the Mg(0.10)-TiO2 film.5 TiO2 still showed the anatase crystal structure after Mg

doping. The XRD patterns also indicate that Mg(II) substituted crystal lattice in anatase TiO2,

which resulted in a higher position of the conduction band minimum (CBM) of the compact

layer. The higher-lying CBM is more compatible with condution bands of the mesoporous

TiO2 and the CH3NH3bPI3, reducing the energy loss though the electron transportation and

leading to the performance enhancement.

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FIG. S4. SEM images of the surfaces of (a) none-doped TiO2, (b) Mg(0.10)-TiO2, and (c)

Mg(0.15)-TiO2 compact films.

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FIG. S5. XPS spectra of Mg(0.10)-TiO2 compact film: (a) Mg 1s, (b) O 1s, and (c) Ti 2p.

The X-ray photoelectron spectroscopy (XPS) spectra are shown in Fig. S5. Fig. S5(a)

shows that Mg 1s peak locates at binding energy of 1303.5 eV which can be attributed to Mg

in Mg-O bonding.6 This implies that Mg incorporation in the films occurred at Ti sites. The O

1s peaks can be observed in Fig. S5(b). The main peak locates at about 529.5 eV due to the

oxygen atoms of TiO2 and MgO. The appearance of 531.5 eV shoulder corresponds to the

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adsorption of OH- groups.7, 8 The existence of OH- is probably due to the deliquescence of

MgO. When Mg-doped TiO2 compact layer was exposed in air, MgO which was formed at

the extreme surface of the film would generate little Mg(OH)2.9 Fig. S5(c) shows that Ti 2p1/2

and Ti 2p3/2 peak binding energies are located at 464.0 eV and 458.3 eV, respectively. The

above-mentioned peaks correspond to Ti4+, showing the existence of titanium dioxides.

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