Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements

Savenije, Tom J.; Guo, Dengyang; Caselli, Valentina M.; Hutter, Eline M.

doi:10.1002/aenm.201903788

Cited by 56 publications

(48 citation statements)

References 89 publications

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“…Microwave conductivity is an established technique for evaluating photoconductivity and charge-carrier lifetime in many types of photoresponsive materials. [39][40][41][42][43][44] In brief, TRMC is a contactless pump-probe technique to monitor the generation and decay of photoinduced free charges in an absorber material on a device-relevant timescale. An optical laser pulse is used to generate mobile charges in a sample located within an X-band waveguide that are continuously probed using %9 GHz resonant microwaves over a 500 ns timescale.…”

Section: Resultsmentioning

confidence: 99%

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

2020

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Lead-based perovskites have benefitted immensely from compositionally tuning away from methylammonium lead iodide (MAPbI 3), giving rise to record-breaking power conversion efficiencies (PCEs), impressive device stabilities, and broadly tunable optoelectronic properties suitable for a vast range of useful applications. [1-8] However, there is currently significant motivation to pursue lead-free perovskite derivatives for a number of reasons that extend beyond the manufacturing and environmental concerns associated with Pb. [9-11] Group 15 metals, such as arsenic, bismuth, and antimony, have shown promise as alternates to Pb outside of Group 14. [12-15] An unavoidable consequence of replacing Pb 2þ with a pnictogen-like Sb 3þ , for example, is that the general AMX 3 perovskite formula transforms to one of their derivatives such as A 3 M 2 X 9 , where A and M are, respectively, monovalent cations (organic/ inorganic) and a metal cation, whereas X predominantly represents halogen anions. There are multiple perovskite derivative substructures accessible to the A 3 M 2 X 9 formula: one is the 0D (dimer) phase with isolated A 2 X 3 9À bioctahedra, and the other is the 2D phase with continuous corrugated layers of polyanions. [16,17] This fact has presented a challenge for researchers seeking to understand and improve these lead-free alternatives for use in solar energy conversion. Due to the large indirect bandgap (2.2-2.5 eV) and poor carrier transport associated with the isolated nature of the 0D polymorph, [18] many groups have focused on targeting the 2D-layered phase, which has a high absorption coefficient, a bandgap on the order of %2 eV, and a comparatively small effective mass in both in-plane and out-of-plane directions, making it the more suitable choice for energy harvesting. [16,19] For this reason, the majority of all-inorganic lead-free perovskite research to date has focused on circumventing the 0D phase to preferentially form the 2D phase, or, to simplify the film fabrication process by achieving the 2D phase at lower temperatures in solution. To date, there has been a lack of focus on the intrinsic photophysics at play as a function of compositional tuning for a fixed substructure. In this article, we will show how photoinduced charge carrier generation, recombination, lifetime, and transport all change within a fixed 2D polymorph of Cs 3 Sb 2 I 9 as a function of alloying Cl À at the X-site, and ultimately how this improves its performance in a solar cell. All-inorganic (Cs þ rather than MA þ at the A-site, for example) Sb-based perovskite derivatives have attracted significant recent interest because of their lower toxicity, [9,13,20,21] better moisture stability, [13,22,23] isoelectronic configuration (ns 2), and comparable defect tolerance compared with Pb analogs. [24-26] For Cs 3 Sb 2 I 9 , the majority of reports have focused on studying

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Section: Resultsmentioning

confidence: 99%

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

2020

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“…For TRMC Measurements, [68] the perovskite films deposited on quartz substrates were mounted in a sealed cavity inside an N 2 -filled glovebox. The TRMC technique measured the change in microwave (8-9 GHz) power on pulsed excitation of the samples at different excitation wavelengths.…”

Section: Methodsmentioning

confidence: 99%

“…Neutral density filters were used to vary the intensity of the incident light. The light-induced change in microwave power was related to the change in conductance ΔG by a sensitivity factor K. [68] The rise of ΔG was limited by the width of the laser pulse (3.5 ns FWHM) and the response time of the microwave system (18 ns). The slow repetition rate of the laser of 10 Hz ensured full relaxation of all photo-induced charges to the ground state before the next laser pulse hits the sample.…”

Section: Methodsmentioning

confidence: 99%

Co‐Evaporated MAPbI₃ with Graded Fermi Levels Enables Highly Performing, Scalable, and Flexible p‐i‐n Perovskite Solar Cells

Dewi

Wang

et al. 2021

Adv Funct Materials

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Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI 3 film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm 2 , achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.

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“…The spatial resolution of SPCM is diffraction-limited and the temporal response is dominated by the carrier transit time and extrinsic metal-semiconductor Schottky effect. In recent years, noncontact methods such as time-resolved microwave conductivity (TRMC) 6,7,16,[22][23][24][25] and time-resolved THz spectroscopy (TRTS) 17,26 are developed to probe the photocarrier dynamics. These far-field techniques, however, do not offer spatially resolved information such as diffusion patterns.…”

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confidence: 99%

Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging

Wang

Chu

et al. 2021

Nat Commun

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The outstanding performance of organic-inorganic metal trihalide solar cells benefits from the exceptional photo-physical properties of both electrons and holes in the material. Here, we directly probe the free-carrier dynamics in Cs-doped FAPbI3 thin films by spatiotemporal photoconductivity imaging. Using charge transport layers to selectively quench one type of carriers, we show that the two relaxation times on the order of 1 μs and 10 μs correspond to the lifetimes of electrons and holes in FACsPbI3, respectively. Strikingly, the diffusion mapping indicates that the difference in electron/hole lifetimes is largely compensated by their disparate mobility. Consequently, the long diffusion lengths (3~5 μm) of both carriers are comparable to each other, a feature closely related to the unique charge trapping and de-trapping processes in hybrid trihalide perovskites. Our results unveil the origin of superior diffusion dynamics in this material, crucially important for solar-cell applications.

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Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements

Cited by 56 publications

References 89 publications

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

Co‐Evaporated MAPbI₃ with Graded Fermi Levels Enables Highly Performing, Scalable, and Flexible p‐i‐n Perovskite Solar Cells

Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging

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Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements

Cited by 56 publications

References 89 publications

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs3Sb2ClxI9–x 2D‐Layered Perovskites

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs3Sb2ClxI9–x 2D‐Layered Perovskites

Co‐Evaporated MAPbI3 with Graded Fermi Levels Enables Highly Performing, Scalable, and Flexible p‐i‐n Perovskite Solar Cells

Superior photo-carrier diffusion dynamics in organic-inorganic hybrid perovskites revealed by spatiotemporal conductivity imaging

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Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

Co‐Evaporated MAPbI₃ with Graded Fermi Levels Enables Highly Performing, Scalable, and Flexible p‐i‐n Perovskite Solar Cells