Why Lead Methylammonium Tri-Iodide Perovskite-Based Solar Cells Require a Mesoporous Electron Transporting Scaffold (but Not Necessarily a Hole Conductor)

Edri, Eran; Kirmayer, Saar; Henning, Alex; Mukhopadhyay, Sabyasachi; Gartsman, K.; Rosenwaks, Y.; Hodes, Gary; Cahen, David

doi:10.1021/nl404454h

Cited by 554 publications

(527 citation statements)

References 22 publications

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“…Therefore, the FTO layers are the n þ þ electrodes. Reports in literature have shown that some lead halide perovskite solar cells behave as p-i-n cells 3,[16][17][18] . Our lead halide perovskites thin films are highly resistive and have low carrier concentrations, typically below the sensitivity of our Hall measurement system (B10 14 cm À 3 ).…”

Section: Resultsmentioning

confidence: 99%

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

et al. 2015

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Efficient lead halide perovskite solar cells use hole-blocking layers to help collection of photogenerated electrons and to achieve high open-circuit voltages. Here, we report the realization of efficient perovskite solar cells grown directly on fluorine-doped tin oxide-coated substrates without using any hole-blocking layers. With ultraviolet-ozone treatment of the substrates, a planar Au/hole-transporting material/CH 3 NH 3 PbI 3-x Cl x /substrate cell processed by a solution method has achieved a power conversion efficiency of over 14% and an open-circuit voltage of 1.06 V measured under reverse voltage scan. The open-circuit voltage is as high as that of our best reference cell with a TiO 2 hole-blocking layer. Besides ultraviolet-ozone treatment, we find that involving Cl in the synthesis is another key for realizing high open-circuit voltage perovskite solar cells without hole-blocking layers. Our results suggest that TiO 2 may not be the ultimate interfacial material for achieving high-performance perovskite solar cells.

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Section: Resultsmentioning

confidence: 99%

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

et al. 2015

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“…It is worth noting here that for devices incorporating mesoporous TiO 2 photoanodes, the neat tri-iodide perovskite functions effi ciently without the need for the extended diffusion length of the photoexcited species. [ 11 ] This is a result of the interpenetrated nature of the collection photoanode, which exhibits pore sizes at the order of tens of nanometers, and in effect reduces the distance electrons must travel to this magnitude before being collected. In the case of planar heterojunctions, electrons must travel the entire thickness of the fi lm, which can sometimes exceed hundreds of nanometers and thus extended diffusion lengths are a requirement for effi cient operation.…”

Section: Doi: 101002/aenm201400355mentioning

confidence: 99%

Solution Deposition‐Conversion for Planar Heterojunction Mixed Halide Perovskite Solar Cells

Docampo

Hanusch

Stranks

et al. 2014

Advanced Energy Materials

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device performance of 15.7% is currently the highest performance achieved for perovskite solar cells, pointing towards planar heterojunction devices as a promising device architecture for further technological improvements.The short circuit currents demonstrated for the devices prepared by Liu and co-workers of 20.4 mA cm −2 , [ 7 ] while high, are still short of the maximum current of over 22 mA cm −2 reasonably achievable, taking into account other light capture losses for this material. [ 3a ] A crucial limitation in this respect is the low diffusion length of around ≈100 nm of the photoexcited species in the MAPbI 3 perovskite. [ 8 ] This parameter can be greatly extended to over 1 µm with the inclusion of chloride in the precursor solution. [ 8a , 9 ] Furthermore, it has been recently shown that the inclusion of chloride is benefi cial for charge transport in the photoactive layer. [ 10 ] It is expected that the addition of chloride results in improved short circuit currents and thus overall photovoltaic performance. It is worth noting here that for devices incorporating mesoporous TiO 2 photoanodes, the neat tri-iodide perovskite functions effi ciently without the need for the extended diffusion length of the photoexcited species. [ 11 ] This is a result of the interpenetrated nature of the collection photoanode, which exhibits pore sizes at the order of tens of nanometers, and in effect reduces the distance electrons must travel to this magnitude before being collected. In the case of planar heterojunctions, electrons must travel the entire thickness of the fi lm, which can sometimes exceed hundreds of nanometers and thus extended diffusion lengths are a requirement for effi cient operation.Here we present planar, fully solution-processed heterojunction solar cells based on the solution deposition-conversion technique. We highlight that chloride is critical in MA lead halide perovskites via a controlled addition of methylammonium chloride (MACl) to the MAI immersion solution. The resulting devices exhibited power conversion effi ciencies approaching 15%, and more importantly, showed short circuit currents of over 22 mA cm −2 , representing a gain of over 10% over stateof-the-art devices. [ 7 ] The parameter most infl uenced by the presence of chloride is the photoluminescence lifetime of the photoexcited species in the device, which reaches values exceeding 300 ns, matching previously reported results for the solution processed mixed halide perovskite fi lms. [ 8a ] Additionally, a reduction of series resistance from 14 to 7 Ω cm 2 was observed.The solar cells developed in this work are composed of a TiO 2 /perovskite/Spiro-MeOTAD planar heterojunction, deposited on a fl uorine-doped tin oxide (FTO) electrode and capped with a gold electrode ( Figure 1 ). The perovskite deposition was performed in two steps: fi rstly, an ≈200 nm PbI 2 fi lm The alkylammonium metal trihalide perovskite absorbers fi rst used in working photovoltaic devices were based on liquid electrolyte sensitized solar cells. Introduc...

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“…[ 17,18 ] MAPbI 3 also appears to exhibit only shallow trap-levels and although the grain boundaries have recently been shown to induce nonradiative decay, [ 19 ] regions only a few tens of nm away from the grain boundaries appear to be unaffected. [ 20,21 ] Furthermore, low Urbach energies, which are extracted from near band edge optical absorption measurements and serve as a benchmark for crystalline phase disorder, indicate low disorder and sharp band edges for lead tri-halide perovskites (15-23 meV). [ 22,23 ] All of these properties contribute to high open-circuit voltages, long charge-carrier lifetimes, and micrometer diffusion lengths, which are crucial for planar-hetero junction photovoltaics.…”

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Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

et al. 2015

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by at least four orders of magnitude. [ 17,18 ] MAPbI 3 also appears to exhibit only shallow trap-levels and although the grain boundaries have recently been shown to induce nonradiative decay, [ 19 ] regions only a few tens of nm away from the grain boundaries appear to be unaffected. [ 20,21 ] Furthermore, low Urbach energies, which are extracted from near band edge optical absorption measurements and serve as a benchmark for crystalline phase disorder, indicate low disorder and sharp band edges for lead tri-halide perovskites (15-23 meV). [ 22,23 ] All of these properties contribute to high open-circuit voltages, long charge-carrier lifetimes, and micrometer diffusion lengths, which are crucial for planar-hetero junction photovoltaics. [ 1,24 ] Nonetheless, these parameters are also expected to depend on the infl uence of crystallization condition on perovskite morphology in fabricated fi lms. [ 25 ] A distinct benefi t of organic-inorganic perovskite materials (e.g., over silicon) is that their bandgap can be tuned relatively easily with chemical composition, allowing attractive coloration and multijunction or tandem cell designs. For example, changing the metal cation at the M site from Pb 2+ to the less toxic Sn 2+ to form CH 3 NH 3 SnI 3 shifts the optical bandgap from 1.55 to 1.3 eV into the range of the "ideal" single-junction solar cell bandgap between 1.1 and 1.4 eV. [ 26,27 ] However, stability issues arising from the oxidation of tin have so far prevented widespread use. Alternatively, tuning the size of the A site cation has been proven to change optical and electronic properties of the perovskite and to signifi cantly infl uence solar cell performance. [ 28 ] Replacing MA in MAPbI 3 by the larger cation formamidinium HC(NH 2 ) 2 + (FA) was found to decrease the bandgap from 1.57 to 1.48 eV, [29][30][31] yield long photoluminescence (PL) lifetimes, high PCEs, [ 28 ] and lower recombination and device hysteresis. [ 32 ] Highest PCEs of 20.1% have been reported [12][13][14] to date for solar cells based on FAPbI 3 making this an attractive system to explore. In addition, the gradual replacement of the MA cation by FA through the fi lm was shown to create a mixed cation-lead-iodide PSC allowing for energetic gradients. [ 33 ] However, mixing of the halide component in the perovskite offers the fi nest tuning of the optical properties of the perovskite fi lm. Here, the mixed organic lead iodide/bromide system has recently gained strong interest for application in PSCs. [ 11,28 ] By changing the ratio between bromide and iodide (at the X site anion), the bandgap can be tailored between 1.55 eV (MAPbI 3 ) and 2.3 eV (MAPbBr 3 ), which results in the coverage of much of the visible spectrum and paves the way for the development of tandem solar cells. [ 11 ] In addition to MAPb(Br y I 1-y ) 3 , its formamidinium relative FAPb(Br y I 1-y ) 3 has been explored. [ 28 ] Most fractional mixtures of FAPb(Br y I 1-y ) 3 were found to be crystalline, with the exception of the region between y = 0.3 and Recent year...

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Why Lead Methylammonium Tri-Iodide Perovskite-Based Solar Cells Require a Mesoporous Electron Transporting Scaffold (but Not Necessarily a Hole Conductor)

Cited by 554 publications

References 22 publications

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

Solution Deposition‐Conversion for Planar Heterojunction Mixed Halide Perovskite Solar Cells

Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

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