All-Inorganic CsPbI 2 Br Perovskite Solar Cells with High Efficiency Exceeding 13% Chong Liu a,, Wenzhe Li a,, Cuiling Zhang b, Yunping Ma b, Jiandong Fan*,a, Yaohua Mai*,a,b a Institute of New Energy Technology, College of Information Science and Technology, Jinan University, Guangzhou, 532, China b Institute of Photovoltaics, College of Physics Science and Technology, Hebei University, Baoding, 712, China *E-mail: (J. F.) jdfan@jnu.edu.cn; *E-mail: (Y. M.) yaohuamai@jnu.edu.cn; The author contributed equally to this work S1
Experimental section Chemicals Lead iodide (99.995%), lead bromide (99.999%), cesium iodide (99.999%), and diethanol amine (99%) were purchased from Alfa Aesar. Dimethyl sulfoxide (anhydrous, 99.9%) and Ni(OCOCH 3 ) 2 4H 2 O (9%) were purchased from Sigma-Aldrich. Isopropanol ( 99.9%) and ethanol (99.5%) were purchased from Aladdin. 1,2-dichlorobenzene (>99.%) was purchased from TCI. C 6 ( 99%) was purchased from Xi an p-oled. ZnO nanoparticle solution (2.5 wt% ZnO in isopropanol) was purchased from Avantama. Film preparation and device fabrication The FTO-coated glass ( Ω sq -1, Beneq TFS 2) was sequentially cleaned with detergent, deionized water, acetone, and alcohol under sonication and then dried under N 2 flow. The glass was treated under oxygen plasma 1 min for further cleaning. The NiO x precursor was prepared by dissolving 5 mg Ni(OCOCH 3 ) 2 4H 2 O in 5 ml ethanol (anhydrous) and 3 μl diethanol amine. The NiO x hole transport layer was obtained by heating the substrates at 4 C for 4 min after spin-coated at 5 rpm for 3 s. The as-prepared NiO x thin film should be treated under oxygen plasma for 2 s before the deposition operation of perovskites. 277 mg PbI 2, 22 mg PbBr 2, and 3 mg CsI were added in 1 ml DMSO, and then heated at 6 C till completely dissolved. The prepared precursor solution was filtered before utilization. The CsPbI 2 Br precursor solution ( μl) was dropped onto the NiO x substrate and spin-coated via a two-step process, the first step is 5 rpm for 3 s, and the second step is 25 rpm for 3 s, respectively. The thin film annealing process was also divided into two steps. Two hotplates controlled respectively at 42 C and C need to be provided for use. After spin-coated, the substrates were firstly placed onto the hotplate with 42 C for about 4 min (depends on the color of the film) to form the transition film. Subsequently, the substrates were placed onto the hotplate with C for 1 min to evaporate the solvents and further enhance the S2
crystallization of perovskites. ZnO nanoparticle solution was diluted by IPA (1:1 by volume) and then spin-coated onto the perovskite thin film at 3 rpm for 3 s. After that, the ZnO nanoparticle-based thin film was post annealed at C for 5 min to completely evaporate the solvent and remove the oxhydryl. C 6 powder was dissolved in 1,2-dichlorobenzene (2mg/mL) and placed overnight at room temperature for use. The C 6 thin film was spin-coated at 2 rpm for 3 s. Finally, 1 nm Ag or Au was thermally deposited under vacuum. Characterization X-Ray Diffraction (XRD) patterns were performed by an X-ray diffractometer Bruker D Advance. Both top-down and cross-sectional scanning electron microscope (SEM) views were measured by FEI Apreo LoVac. Ultraviolet photoelectron spectroscopy (UPS) spectra were obtained with a Thermo Fisher Scientific K-ALPHA +, using the HeI (21.22eV) emission line. PL lifetime was measured by the time-correlated single photon counting method with an Edinburgh Instruments FLS9 fluorescence spectrometer. The excitation source was used a picosecond pulsed diode laser at 45 nm. The Current density-voltage (J-V) curves of perovskite solar cells were recorded using a Keithley 24 source measurement unit and a Newport solar simulator (ORIEL-SOI3A) with an AM1.5G spectrum. The light intensity was adjusted to 1 mw/cm 2 using standard Si cell (9115V). The effective working area was controlled by placing a shadow mask with an aperture (9 mm 2 ) on the devices. Both forward and reverse scan were measured with the scanning speed of.15 V/s. The external quantum efficiency (EQE) spectra were measured in DC mode on a spectrum corresponding system (Enlitech QE-R), calibrated by Si reference solar cell. S3
Figure S1. Top-down SEM image for CsPbI 2 Br deposited without the transition film. S4
(a) (b) Ag ZnO C 6 CsPbI 2 Br NiO x 1 μm FTO (c) (d) Roi Ag C 6 Perovskite C Ag Distance (e) Current Density (ma/cm 2 ) 4 ZnO (Reverse) ZnO (Forward) C 6 (Reverse) C 6 (Forward)..2.4.6. 1. Voltage (V) (f) EQE (%) 1 6 4 2 ZnO C 6 2 nm 3 4 5 6 7 Wavelength (nm) Figure S2. Cross-sectional SEM images of (a) ZnO-based PSC; (b) C 6 -based PSC. (c) Top-down SEM image for ZnO nanoparticle-based layer deposited on perovskite thin film. (d) The EDS line scanning of the single C 6 layer-based device. (e) J-V curves with forward and reverse scan for ZnO- and C 6 -based PSC. (f) EQE of ZnO- and C 6 - based PSCs, respectively. Figure S2a shows the cross-sectional SEM image of the ZnO-based device, where both the interfaces between perovskite/electrode (black frame) and ZnO/electrode (red frame) exhibit inferior contact, which was associated with the pinholes on the surface of ZnO film (Figure S2c). Such interface conditions would potentially result in large leakage loss and contact resistance, which gives rise to a sharp s-shape J-V curve and low photovoltaic performance (Figure S2e, red line). In comparison, the single C 6 layer can be uniformly coated and form ideal interface contact with perovskite S5
layer and electrode (Figure S2b and S2d). Nevertheless, the C 6 -based solar cells showed a 9.5% PCE in reverse scan and 5.2% in forward scan (Figure S2e, blue line). Considering the electron mobility of C 6 ETL (1.6 cm 2 V -1 s -1 ) is at least three orders of magnitude higher than the hole mobility of NiO x HTL (1-5 to 1-3 cm 2 V -1 s -1 ), 1,2 we assume that the serious hysteresis effect was ascribed to the mismatched ability of charge transportation for the ETL and HTL, which resulted in the charge accumulation in interfacial domain. Comparably, the electron mobility of ZnO nanoparticle is 2 1-3 cm 2 V -1 s -1, 3 which is more suitable to match with the NiO x HTL in this regard. Equally importantly, the external quantum efficiency (EQE) of ZnO- and C 6 - based PSCs are proved to be complementary for each other (Figure S2f). In particular, the spectral response of ZnO-based PSC is insufficient in the range of 3-515 nm in contrast the enhanced response of C 6 -based PSCs, whereas a decreased response of ZnO-based PSCs in the range of 515-65 nm in comparison to that of C 6 -based PSCs. UPS Intensity (a.u.).7 1.73 21 2 19 1 17 4 2 Binding Energy (ev) Figure S3. UPS cutoff spectra of CsPbI 2 Br thin film. E F = 21.22 ev -.7 ev = 4.35 ev; E VBM = 4.35 ev + 1.73 ev =6. ev; E CBM = 6. ev 1.92 ev = 4. ev. S6
Current Density (ma/cm 2 ) 14 1 6 4 2 Reverse Scan Forward Scan..2.4.6. 1. 1.2 Voltage (V) Figure S4. J-V curves of the champion PSC with reverse and forward scan, respectively. 25 2 [Eln(1-EQE)] 2 15 1 5 1.92 ev 1.6 1.7 1. 1.9 2. 2.1 2.2 E (ev) Figure S5. The bandgap of CsPbI 2 Br thin film calculated from the EQE spectra. 4 S7
Figure S6. The cross-sectional and top-down SEM images of MAPbI 3 and CsPbI 2 Br upon electron beam illumination with different time. Upon the illumination of electron beam, the MAPbI 3 perovskite thin film tend to be degenerated with electron-beam soaking time, whereas the CsPbI 2 Br thin film and solar cell remain exactly same morphology and structure. S
J sc (ma/cm 2 ) FF Normalized PCE (%) 1 14.9..7.6.5.4 1..5. (a) (c) (e) Ag electrode Au electrode Ag electrode Au electrode 5 C (b) (d) Ag electrode Au electrode Ag electrode Au electrode Au electrode Ag electrode 5 1 15 2 25 Time (h) 1.2 1.1 1..9 14 1 6 V oc (V) PCE (%) Figure S7. (a-d) The photovoltaic performances of Au- and Ag-based solar cells. (e) The thermal stability test of the corresponding devices. S9
(a) J SC (ma/cm 2 ). 1...6 1 V OC (V) (c) Current Density (ma/cm 2 ) FF J SC (ma/cm 2 ) FF 4 (b).6.4 2..7.6.5.4 Figure S. The efficiency statistics charts and representative J-V curves at different heating time. 24 36 4 96 144 192 Inorganic-h Inorganic-h Inorganic-24h Inorganic-36h Time (h) Time (h)..2.4.6. 1. Voltage (V) (d) Current Density (ma/cm 2 ) 24 36 4 96 144 192 2 15 1 5 Hybrid- h Hybrid- 4h Hybrid- 96h Hybrid- 144h Hybrid- 192h 6 4 1.1 1..9 15 1 5 PCE (%) V OC (V) PCE (%)..2.4.6. 1. Voltage (V) S1
Table S1. Parameters of the TRPL spectroscopy based on different ETLs. Samples τ 1 (ns) A 1 (%) τ 2 (ns) A 2 (%) τ ave (ns) Without ETL.6 5.5 2.64 41.5 1.45 ZnO@C 6.39 79.7 2.6 2.3.73 ZnO.53 51.2 2.3 4. 1.43 C 6.47 75.9 2.4 24.1 1.4 The τ ave is calculated by the formula 5 ave i A i i Reference (1) Liang, P.-W.; Chueh, C.-C.; Williams, S. T.; Jen, A. K. Y. Adv. Energy Mater. 215, 5, 142321. (2) Chen, W.; Wu, Y.; Liu, J.; Qin, C.; Yang, X.; Islam, A.; Cheng, Y.-B.; Han, L. Energy Environ. Sci. 215,, 629. (3) Qian, L.; Zheng, Y.; Xue, J.; Holloway, P. H. Nature Photo. 211, 5, 543. (4) Li, J.; Wang, H.; Wu, L.; Chen, C.; Zhou, Z.; Liu, F.; Sun, Y.; Han, J.; Zhang, Y. ACS appl. Mater. Interfaces 2,, 123. (5) Heo, J. H.; Han, H. J.; Kim, D.; Ahn, T. K.; Im, S. H. Energy Environ. Sci. 215,, 2. S11