Supporting Information Inorganic Halide Perovskites for Efficient Light ...
Supporting Information
Inorganic Halide Perovskites for Efficient Light Emitting Diodes Natalia Yantara1, Saikat Bhaumik1, Fei Yan2, Dharani Sabba1, Herlina A. Dewi1, Nripan Mathews*,1,3, Pablo P. Boix*, 1 , Hilmi Volkan Demir2, Subodh Mhaisalkar1,3. 1
Energy Research Institute@NTU (ERI@N), Research TechnoPlaza, X-Frontier Block, Level 5, 50 Nanyang Drive, 637553, Singapore. 2
LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore. 3
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
Photoelectron spectroscopy in air (PESA) spectra of CsPbBr3 films from various CsBr/PbBr2 ratios
Figure S1. PESA spectra of both (1-1) and (2-1) films.
1
Study on the stability of CsPbBr3 based PeLED
Figure S2. EL intensity and J of devices (A) together with the carrier injection efficiency (ηA) (B) with (2-1) film versus time.
The stability of the encapsulated CsPbBr3 based PeLED was tested at 7 V driving voltages. Exponential degradation rate of the J and L was noticed and ηA remains similar over the same time interval. Impact of CsBr/PbBr2 ratio on the optoelectronic properties of the film Solutions with varied CsBr/PbBr2 ratio (i.e. 0.8, 1.0, 2.0, and 3.0) were made in DMSO solvent (Figure S3a). After stirring for 5 h in room temperature, clear solutions were obtained from solutions with CsBr/PbBr2 ratio of 0.8 and 1.0. On the other hand, precipitates were observed for solutions with CsBr/PbBr2 ratio of 2.0 and 3.0. Films deposited from the solutions were characterized with XRD and reported in Figure S3b. Polycrystalline CsPbBr3 film (Pnma crystal structure) with additional CsPb2Br5 phase was observed on the film deposited from PbBr2 rich solution (i.e. CsBr/PbBr2 ratio of 0.8). The presence of CsPb2Br5 peak disappeared with increasing the CsBr/PbBr2 ratio and pure CsPbBr3 were observed for films with CsBr/PbBr2 ratio ≥1.0.
2
Figure S3. The images of the solutions made with various CsBr/PbBr2 ratio (A) together with the XRD spectra of the films deposited from the solutions (B). The photoluminescence quantum yield (PLQY) and photoluminescence (PL) lifetime of CsPbBr3 thin films made from varied CsBr/PbBr2 ratio are characterized and presented in Figure S4. Films from 0.8 CsBr/PbBr2 ratios solution suffer with low PLQY and PL lifetime, which might be related to the existence of CsPb2Br5 impurity on the film. Enhancement on both the PL lifetime and PLQY was observed when CsBr rich solutions were used up to CsBr/PbBr2 ratio of 2.0, signifying lower non radiative defects densities. Further increment on the CsBr content (i.e. CsBr/PbBr2 ratio of 3.0) degrades the PL lifetime and PLQY. Therefore, devices were made from equimolar (i.e. CsBr/PbBr2 ratio of 1.0) and CsBr rich solution (CsBr/PbBr2 ratio of 2.0) to understand its impact on the LED performances. PLQY enhancement with prolong air exposure was observed for all films deposited from equimolar and CsBr rich samples. However, extended air exposure decreases the PLQY of the films with PbBr2 rich samples which might be attributed to the presence of CsPb2Br5 impurity that could affect the stability of CsPbBr3 film.
3
Figure S4. The time resolved photoluminescence decay curve of films made from various CsBr/PbBr2 ratios (A). The PLQYs and their evolution measured at different time after storing in air (relative humidity of ±70%) is also presented (B).
Reproducibility of PeLEDs A total of 6 devices were analyzed for each parameter and the distribution of the luminescence (L) and voltage (V) curves for all the PeLEDs are presented in Figure S5. The threshold voltage (Vth) of devices from CsBr rich solution (2-1) is consistently lower than from equimolar solution (1-1). On the other hand, the maximum luminescence (Lmax) of devices with (2-1) is higher than Lmax of (1-1) The behavior of the devices analyzed in the main text is representative of this general trend.
Figure S5. The L-V curves for all devices made with equimolar (1-1) and CsBr rich (2-1) solutions. The variation on the Lmax and Vth of both (1-1) and (2-1) are highlighted with shaded orange and blue respectively.
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Effect of CsBr/PbBr2 ratio on the solar cell performances The impact on the solar cell performances were further studied in planar configuration (FTO/TiO2/CsPbBr3/spiro-MeOTAD/Au). TiO2 blocking layer was prepared via spray pyrolysis at 450°C on top of Fluorine doped tin oxide (FTO, TEC 15) coated glasses. TiO2 films were treated with 100mM TiCl4 for 1 h at 70°C and then rinsed with de-ionized water before annealing at 500°C for 30 mins. CsPbBr3 were spun coated on top from equimolar and CsBr rich solutions and followed by annealing at 70°C for 30 mins. Solution containing 100 mg/mL SpiroMeOTAD in chlorobenzene mixed with 10µl of tert-butylpyridine and 31µl of 170 mg/mL Lithium bis(trifluoromethane)sulfonamide in acetonitrile was spun coated on top at 4000 rpm for 30 s. The devices were then completed with thermally evaporated Au film. The preliminary study on the current density (J) and voltage (V) curves of devices made from equimolar (i.e. S1-1) and CsBr rich (i.e. S2-1) solutions under dark and illumination condition are represented in Figure S6. The solar cell efficiencies (η) of (S2-1) were superior than (S1-1) due to better Voc, Jsc, and FF. The enhancement of Jsc and FF with CsBr rich solution could be explained by the better charge transport and lower trap density of films from CsBr rich solution respectively. Lower hysteresis index (calculated according to a report from Sanchez et al1) was observed for (S2-1) than (S1-1). The existence of pin holes on the CsPbBr3 films might contributes to the low Jsc and ultimately η of the devices as compared to the literatures2. This phenomenon is in agreement with the outcomes observed from the LED devices made from equimolar and CsBr rich solution.
Figure S6. The dark and light J-V curves of the CsPbBr3 based solar cells made from equimolar (S1-1) and CsBr rich solution (S2-1) scan from open voltage to short circuit condition (i.e. reverse) and vice versa (i.e. forward).
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References (1)
Sanchez, R. S.; Gonzalez-Pedro, V.; Lee, J. W.; Park, N. G.; Kang, Y. S.; Mora-Sero, I.; Bisquert, J. Slow Dynamic Processes in Lead Halide Perovskite Solar Cells. Characteristic Times and Hysteresis. J. Phys. Chem. Lett. 2014, 5, 2357–2363.
(2)
Kulbak, M.; Cahen, D.; Hodes, G. How Important Is the Organic Part of the Lead Halide Perovskite Photovoltaic Cells? Efficient CsPbBr3 Cells. J. Phys. Chem. Lett. 2015, 6, 2452–2456.
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Inorganic Halide Perovskites for Efficient Light Emitting Diodes Natalia Yantara1, Saikat Bhaumik1, Fei Yan2, Dharani Sabba1, Herlina A. Dewi1, Nripan Mathews*,1,3, Pablo P. Boix*, 1 , Hilmi Volkan Demir2, Subodh Mhaisalkar1,3. 1
Energy Research Institute@NTU (ERI@N), Research TechnoPlaza, X-Frontier Block, Level 5, 50 Nanyang Drive, 637553, Singapore. 2
LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore. 3
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
Photoelectron spectroscopy in air (PESA) spectra of CsPbBr3 films from various CsBr/PbBr2 ratios
Figure S1. PESA spectra of both (1-1) and (2-1) films.
1
Study on the stability of CsPbBr3 based PeLED
Figure S2. EL intensity and J of devices (A) together with the carrier injection efficiency (ηA) (B) with (2-1) film versus time.
The stability of the encapsulated CsPbBr3 based PeLED was tested at 7 V driving voltages. Exponential degradation rate of the J and L was noticed and ηA remains similar over the same time interval. Impact of CsBr/PbBr2 ratio on the optoelectronic properties of the film Solutions with varied CsBr/PbBr2 ratio (i.e. 0.8, 1.0, 2.0, and 3.0) were made in DMSO solvent (Figure S3a). After stirring for 5 h in room temperature, clear solutions were obtained from solutions with CsBr/PbBr2 ratio of 0.8 and 1.0. On the other hand, precipitates were observed for solutions with CsBr/PbBr2 ratio of 2.0 and 3.0. Films deposited from the solutions were characterized with XRD and reported in Figure S3b. Polycrystalline CsPbBr3 film (Pnma crystal structure) with additional CsPb2Br5 phase was observed on the film deposited from PbBr2 rich solution (i.e. CsBr/PbBr2 ratio of 0.8). The presence of CsPb2Br5 peak disappeared with increasing the CsBr/PbBr2 ratio and pure CsPbBr3 were observed for films with CsBr/PbBr2 ratio ≥1.0.
2
Figure S3. The images of the solutions made with various CsBr/PbBr2 ratio (A) together with the XRD spectra of the films deposited from the solutions (B). The photoluminescence quantum yield (PLQY) and photoluminescence (PL) lifetime of CsPbBr3 thin films made from varied CsBr/PbBr2 ratio are characterized and presented in Figure S4. Films from 0.8 CsBr/PbBr2 ratios solution suffer with low PLQY and PL lifetime, which might be related to the existence of CsPb2Br5 impurity on the film. Enhancement on both the PL lifetime and PLQY was observed when CsBr rich solutions were used up to CsBr/PbBr2 ratio of 2.0, signifying lower non radiative defects densities. Further increment on the CsBr content (i.e. CsBr/PbBr2 ratio of 3.0) degrades the PL lifetime and PLQY. Therefore, devices were made from equimolar (i.e. CsBr/PbBr2 ratio of 1.0) and CsBr rich solution (CsBr/PbBr2 ratio of 2.0) to understand its impact on the LED performances. PLQY enhancement with prolong air exposure was observed for all films deposited from equimolar and CsBr rich samples. However, extended air exposure decreases the PLQY of the films with PbBr2 rich samples which might be attributed to the presence of CsPb2Br5 impurity that could affect the stability of CsPbBr3 film.
3
Figure S4. The time resolved photoluminescence decay curve of films made from various CsBr/PbBr2 ratios (A). The PLQYs and their evolution measured at different time after storing in air (relative humidity of ±70%) is also presented (B).
Reproducibility of PeLEDs A total of 6 devices were analyzed for each parameter and the distribution of the luminescence (L) and voltage (V) curves for all the PeLEDs are presented in Figure S5. The threshold voltage (Vth) of devices from CsBr rich solution (2-1) is consistently lower than from equimolar solution (1-1). On the other hand, the maximum luminescence (Lmax) of devices with (2-1) is higher than Lmax of (1-1) The behavior of the devices analyzed in the main text is representative of this general trend.
Figure S5. The L-V curves for all devices made with equimolar (1-1) and CsBr rich (2-1) solutions. The variation on the Lmax and Vth of both (1-1) and (2-1) are highlighted with shaded orange and blue respectively.
4
Effect of CsBr/PbBr2 ratio on the solar cell performances The impact on the solar cell performances were further studied in planar configuration (FTO/TiO2/CsPbBr3/spiro-MeOTAD/Au). TiO2 blocking layer was prepared via spray pyrolysis at 450°C on top of Fluorine doped tin oxide (FTO, TEC 15) coated glasses. TiO2 films were treated with 100mM TiCl4 for 1 h at 70°C and then rinsed with de-ionized water before annealing at 500°C for 30 mins. CsPbBr3 were spun coated on top from equimolar and CsBr rich solutions and followed by annealing at 70°C for 30 mins. Solution containing 100 mg/mL SpiroMeOTAD in chlorobenzene mixed with 10µl of tert-butylpyridine and 31µl of 170 mg/mL Lithium bis(trifluoromethane)sulfonamide in acetonitrile was spun coated on top at 4000 rpm for 30 s. The devices were then completed with thermally evaporated Au film. The preliminary study on the current density (J) and voltage (V) curves of devices made from equimolar (i.e. S1-1) and CsBr rich (i.e. S2-1) solutions under dark and illumination condition are represented in Figure S6. The solar cell efficiencies (η) of (S2-1) were superior than (S1-1) due to better Voc, Jsc, and FF. The enhancement of Jsc and FF with CsBr rich solution could be explained by the better charge transport and lower trap density of films from CsBr rich solution respectively. Lower hysteresis index (calculated according to a report from Sanchez et al1) was observed for (S2-1) than (S1-1). The existence of pin holes on the CsPbBr3 films might contributes to the low Jsc and ultimately η of the devices as compared to the literatures2. This phenomenon is in agreement with the outcomes observed from the LED devices made from equimolar and CsBr rich solution.
Figure S6. The dark and light J-V curves of the CsPbBr3 based solar cells made from equimolar (S1-1) and CsBr rich solution (S2-1) scan from open voltage to short circuit condition (i.e. reverse) and vice versa (i.e. forward).
5
References (1)
Sanchez, R. S.; Gonzalez-Pedro, V.; Lee, J. W.; Park, N. G.; Kang, Y. S.; Mora-Sero, I.; Bisquert, J. Slow Dynamic Processes in Lead Halide Perovskite Solar Cells. Characteristic Times and Hysteresis. J. Phys. Chem. Lett. 2014, 5, 2357–2363.
(2)
Kulbak, M.; Cahen, D.; Hodes, G. How Important Is the Organic Part of the Lead Halide Perovskite Photovoltaic Cells? Efficient CsPbBr3 Cells. J. Phys. Chem. Lett. 2015, 6, 2452–2456.
6
