Improving Efficiency and Reproducibility of Perovskite Solar Cells through Aggregation Control in Polyelectrolytes Hole Transport Layer

Transcription

1 Supporting Information Improving Efficiency and Reproducibility of Perovskite Solar Cells through Aggregation Control in Polyelectrolytes Hole Transport Layer Xiaodong Li, a Ying-Chiao Wang, a Liping Zhu, a Wenjun Zhang, a,b Hai-Qiao Wang a,b and Junfeng Fang* a,b a Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, , China. fangjf@nimte.ac.cn b University of Chinese Academy of Sciences, Beijing , China S-1

2 Experimental section Materials: P3CT-Na was synthesized through the reaction of poly[3-(4-carboxylbutyl)thiophene (P3CT, Mw: 30-40k, Rieke Metals) with sodium hydroxide (NaOH, molar ratio 1:1) in H 2 O at 60 o C under stirring. P3CT-CH 3 NH 2 was obtained with the same method but using CH 3 NH 2 in methanol solvent. Devices fabrication: The ITO/glass substrate was cleaned by successive sonication in detergent, deionized water, acetone and isopropyl alcohol, and then dried by nitrogen flow. Then the ITO substrates were treated by O 2 -plasma for 2min. For flexible devices, the PET/ITO substrates were directly used without sonication cleaning or O 2 -plasma. The P3CT-CH 3 NH 2 (1mg/mL in methanol) or P3CT-Na (2mg/mL in H 2 O) was spincoated on ITO at 4000 rpm 60s. After thermal annealing at 100 o C for 10min in air, the substrates were transferred into glove box filled with N 2. The perovskite precursor solution was prepared by dissolving CH 3 NH 3 I and PbI 2 (1:1, 1.45M) in 1mL mixed solvent of DMF and DMSO (Volume ratio 4:1). Perovskite films were fabricated using anti-solvent method at 4800rpm 20s. And the anti-solvent chlorobenzene (CB, 300µL) was added on the substrate at 10s after the spincoating started. Then the substrate was put on hotplate at 60 o C 1min and 100 o C 3min to form perovskite films. After the substrate cooled to room-temperature, PCBM solution (10mg/mL in CB) was spin-coated on perovskite films at 2000rpm 60s.Then the substrate was transferred to vacuum chamber. 20nm C60, 8nm BCP and 100nm Ag was deposited by thermal evaporation using a metal shadow mask. The device area was 6mm 2. Device characterization: The J-V curves were measured using Keithley 2440 sourcemeter controlled by computer. All the solar cells were measured under simulated AM 1.5G spectrum (100 mw/cm 2 ) with S-2

3 an Oriel So13A solar simulator. The EQE measurement was conducted through the Newport quantum efficiency measurement system (ORIEL IQE 200TM) combined with a lock-in amplifier and 150 W xenon lamp. The light intensity at each wavelength was calibrated by one standard Si/Ge solar cell. EQE was measured in air at room temperature. Hole Mobility Measurement: Hole-only devices were fabricated to measure the hole mobility of polyelectrolytes interlayer through space charge limited current (SCLC) method (ITO/MoO 3 /P3CT-Na or P3CT-CH 3 NH 2 /MoO 3 /Al). The mobility was calculated by fitting the dark current to the model of a single carrier SCLC. According to the equation: J = (9/8)ε 0 ε r µ((v 2 )/(L 3 )), where J, µ, ε 0, ε r, L and V is current density, zero-field mobility, permittivity of free space, the relative permittivity of the material, thickness of active layer and effective voltage respectively. The hole mobility can be calculated from the slope of the J 1/2 ~V curves. S-3

4 Figure S1. The photograph of P3CT-Na in methanol and H 2 O, P3CT-CH 3 NH 2 in methanol with density of 1mg/mL. The powder at the bottom of bottle for P3CT-Na in methanol indicates that P3CT-Na cannot be dissolved in methanol and only dissolved in more polar solvent (H 2 O). While P3CT-CH 3 NH 2 is easy to be dissolved in methanol. The solution color of P3CT-Na in H 2 O is dark red, and the solution of P3CT-CH 3 NH 2 is orange, indicating the suppressed aggregation of P3CT-CH 3 NH 2. S-4

5 Figure S2. Dynamic light scattering (DLS) measurement of P3CT-Na and P3CT-CH 3 NH 2 with the same density of 0.5 mg/ml. P3CT-CH 3 NH 2 exhibits one narrow size distribution around 56 nm. While P3CT-Na shows broad size distribution from 15 nm to 100 nm, and even a small peak around 4000 nm is observed. The DLS data further confirms the severe aggregation of P3CT-Na compared with P3CT-CH 3 NH 2. Figure S3. Fitted line of hole mobility measurement using SCLC method. S-5

6 Figure S4. SEM images of thick perovskite (~500nm) prepared on ITO/P3CT-Na or ITO/P3CT-CH 3 NH 2. The thick perovskite films are used to simulate the morphology at top interface (the side away from ITO). Whether coated on P3CT-Na or on P3CT-CH 3 NH 2, the perovskite films are compact and uniform, indicating that the interlayer coated on ITO would not affect the morphology at top interface. S-6

7 Figure S5. Enlarged normalized PL spectra of perovkite films on P3CT-Na and P3CT-CH 3 NH 2. Figure S6. Stabilized power output at the maximum power point (MPP) of perovskite solar cells with P3CT-CH 3 NH 2 on rigid Glass/ITO substrate. Device is measured under 0.92 V. S-7

8 Figure S7. a) Full UPS spectra b) secondary-electron cutoff c) XPS spectra of P3CT-Na and P3CT-CH 3 NH 2 coated on ITO substrate. From UPS data, after P3CT-Na or P3CT-CH 3 NH 2 modification, the work function (WF) of ITO is effectively increased. The WF of ITO/P3CT-Na and ITO/P3CT-CH 3 NH 2 is almost the same (5.23 ev and 5.25 ev respectively). In XPS spectra, peak characteristic of N 1s can be observed in P3CT-CH 3 NH 2, and peak characteristic of Na 1s is observed in P3CT-N. S-8

9 Figure S8. Average Shifted Histogram of device efficiency with a) P3CT-Na, b) P3CT-CH3NH2 interlayer, c) standard box plot of device efficiency. Figure S9. a) Photocurrent hysteresis in large area devices (1 cm 2 ) with P3CT-CH 3 NH 2 ; b) Efficiency distribution among 25 separated devices (1 cm 2 ) with P3CT-CH 3 NH 2 interlayer. S-9

10 Figure S10. a) Photocurrent hysteresis b) Stabilized power output at the maximum power point (MPP) of flexible perovskite solar cells with P3CT-CH 3 NH 2 interlayer. Figure S11. J-V curves of flexible perovskite solar cells with P3CT-CH 3 NH 2 after different bending cycle. S-10

11 Figure S12. 1 H NMR of P3CT in DMF and P3CT-CH 3 NH 2 in CD3OD. S-11

12 Figure S13. J-V hysteresis of P3CT-Na based devices on rigid Glass/ITO substrate. S-12

13 Figure S14. J-V curve of P3CT-Na based devices on flexible PET/ITO substrate. S-13

14 Table S1. The fitted results of time-solved photoluminescence decay in perovskite coated on P3CT-Na and P3CT-CH 3 NH 2. Substrate Interlayer τ 1 τ 2 lifetime (ns) content (%) lifetime (ns) content (%) Rigid Glass/ITO P3CT-Na P3CT-CH 3 NH Table S2. Device parameters of perovskite solar cells with P3CT-Na or P3CT-CH 3 NH 2 on rigid substrate. Substrate Interlayer V oc (V) J sc (ma/cm 2 ) FF (%) PCE (%) Rigid Glass/ITO P3CT-Na (18.3 a ) P3CT-CH 3 NH (19.6) a parameters in brackets are the average PCE. The average PCE is among 100 separated device. S-14