This document summarizes research on improving the efficiency of perovskite solar cells through the use of hydrothermally fabricated TiO2 heterostructures. TiO2 nanorods and nanoparticles were prepared via a two-step hydrothermal process and spin-coated to form different heterostructure electron transport layers (ETLs). The optimal ETL contained TiO2 nanoparticles prepared with 0.066M TTIP and exhibited a power conversion efficiency of 14.143% due to improved carrier extraction, reduced charge recombination, light scattering, and trap state passivation at the ETL/perovskite interface. Future work will focus on efficient spin-coating methods for high performance TiO2 nanorod-based perovskite solar cells with uniform

1. Hydrothermal fabricated TiO2 heterostructure
boosts efficiency of MAPbI3 perovskite solar cells
2021/07/12

2. Introduction
2
Perovskite solar cells
(Mesoporous structure)
Metal halide perovskite
One-dimensional (1-D) TiO2
nanostructures
Hydrothermal method
 Reduce the
recombination
of e/h+.
 Improve the
electron
transport.
 Large surface
area.
Vertical TiO2 nanorods
(TNRs) on FTO glass
 The simple implementation
process.
 Low cost and safety.
 Obtained nanorod structure has
high homogeneity, crystallinity.
e- e- e-
e- e-
(TNP: TiO2 nanoparticle)

3. Enhance efficiency of PSCs based on TiO2
heterostructures
3
Incident light
Scattering
phenomena
CB
VB

4. Preparation of TNRs/TNPs heterostructures
4
Drying
Stirring
1 hour 15 min
TTIP (x M) Ethanol (20 ml)
5 ml Ethanol/DI water
(volume ratio: 4/1)
Stirring
Annealing
(500oC, 1h)
Washing
Device x (M)
RP0 0
RP1 0.033
RP2 0.066
RP3 0.1
Hydrothermal
process (90oC, 10h)

5. Preparation of TNRs/P25 heterostructures (RCP25)
5
40 mg/ml P25 TiO2
nanoparticles in
Ethanol
Spin-coating
3000 rpm, 30s
Drying
Annealing
(500oC, 1h)

6. Top SEM images
6
RP0 RP1 RP2
RP3 RCP25

7. Cross-sectional SEM images
7
RP0 RP1 RP2
RP3 RCP25

8. XRD results
8

9. TEM images
9
10 µm
TEM HRTEM SAED

10. Performance of solar cells
10
Device
Jsc
(mA/cm2
)
Voc (V) FF (%)
Efficiency
(%)
RP0 18.169 0.958 53.782 9.361
RP1 19.438 0.984 51.222 9.797
RP2 22.507 1.048 59.960 14.143
RP3 21.443 1.036 54.050 12.007
RCP25 20.443 0.997 49.636 10.117

11. External quantum efficiency (EQE) measurement
11

12. UV-Vis absorption
12
Incident light
Incident light
Light scaterring
Light scaterring
RCP25
RP2

13. Electrochemical impedance spectroscopy (EIS)
measurement
13
Device Rct (Ω)
RP0 64.401
RP1 61.848
RP2 17.373
RP3 30.833
RCP25 50.467
Rct: Charge transfer resistance
RFTO

14. The space charge limited current (SCLC) measurement
14
Nt = 2εεoVtfte-1d-2
Device Nt (cm-3
)
RP0 (a) 1.595 x 1016
RP1 (b) 1.500 x 1016
RP2 (c) 1.107 x 1016
RP3 (d) 1.329 x 1016
RCP25 (e) 1.440 x 1016
Trap-state density (Nt):
(Vtft: trap-filled limit voltage,
L: thickness of perovskite
film, ε: the relative dielectric
constant of perovskite, εo:
the vacuum permittivity)

15. Conclusion
 Anatase TNPs/rutile TNRs heterostructures were successfully obtained by two-steps
hydrothermal process. P25 nanoparticles/ TNRs ETL was also prepared by a simple spin-
coating method.
 Compared with pure rutile TNRs based PSCs, the devices based on TiO2 heterostructures
exhibited an improvement in performance.
 The optimal ETLs was RP2, which contains TNPs prepared by the second hydrothermal
process with 0.066M TTIP. The champion PCE of the device based on this ETL was 14.143 %.
 This remarkable performance is assigned to the improvement of carrier extraction
capability, the reduction of charge recombination, the light scattering phenomena, and the
passivation of trap states at the ETL/perovskite interface.
15

16. Future plan
 Research on efficient spin-coating method for TiO2 nanorods-based perovskite solar cells with high
performance and uniformity
16
10 20 30 40 50 60 70 80 90
(116)
(220)
Intensity
(a.u.)
2q (degree)
TNR-PSK (DMF-IPA_2steps)
TNR-PSK (DMF-DMSO_1 step)
New method
(110)
(a)
(b)
(c)
MAI
PbI2
MA solution
in Ethanol +
Acetonitrile
Pre-heating at 70oC
Dynamic spin-coating
3000 rpm, 30 s

17. Thank you for your attention !
17