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Title: Band Tailing and Deep Defect States in CH 3NH 3Pb(I 1–xBr x) 3 Perovskites As Revealed by Sub-Bandgap Photocurrent

Abstract

Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. In this paper, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH 3NH 3Pb(I 1–xBr x) 3/TiO 2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (E u) over the full halide composition space. The Urbach energies are 15–23 meV, lower than those for most semiconductors with similar bandgaps (especially with E g > 1.9 eV). Intentional aging of CH 3NH 3Pb(I 1–xBr x) 3 for up to 2300 h, reveals no change in E u, despite the appearance of the PbI 2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH 3NH 3PbI 3 or mixed CH 3NH 3Pb(I 1–xBr x) 3 compositions, respectively. Finally, the study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH 3NH 3Pb(I 1–xBr x)more » 3 alloys.« less

Authors:
ORCiD logo [1];  [2];  [1];  [2];  [3]; ORCiD logo [3];  [2];  [1]
  1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Univ. of Oregon, Eugene, OR (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); LBNL Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1379750
Grant/Contract Number:
AC02-05CH11231; SC0012363
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Energy Letters
Additional Journal Information:
Journal Volume: 2; Journal Issue: 3; Journal ID: ISSN 2380-8195
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Sutter-Fella, Carolin M., Miller, D. Westley, Ngo, Quynh P., Roe, Ellis T., Toma, Francesca M., Sharp, Ian D., Lonergan, Mark C., and Javey, Ali. Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent. United States: N. p., 2017. Web. doi:10.1021/acsenergylett.6b00727.
Sutter-Fella, Carolin M., Miller, D. Westley, Ngo, Quynh P., Roe, Ellis T., Toma, Francesca M., Sharp, Ian D., Lonergan, Mark C., & Javey, Ali. Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent. United States. doi:10.1021/acsenergylett.6b00727.
Sutter-Fella, Carolin M., Miller, D. Westley, Ngo, Quynh P., Roe, Ellis T., Toma, Francesca M., Sharp, Ian D., Lonergan, Mark C., and Javey, Ali. Wed . "Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent". United States. doi:10.1021/acsenergylett.6b00727. https://www.osti.gov/servlets/purl/1379750.
@article{osti_1379750,
title = {Band Tailing and Deep Defect States in CH3NH3Pb(I1–xBrx)3 Perovskites As Revealed by Sub-Bandgap Photocurrent},
author = {Sutter-Fella, Carolin M. and Miller, D. Westley and Ngo, Quynh P. and Roe, Ellis T. and Toma, Francesca M. and Sharp, Ian D. and Lonergan, Mark C. and Javey, Ali},
abstractNote = {Organometal halide perovskite semiconductors have emerged as promising candidates for optoelectronic applications because of the outstanding charge carrier transport properties, achieved with low-temperature synthesis. In this paper, we present highly sensitive sub-bandgap external quantum efficiency (EQE) measurements of Au/spiro-OMeTAD/CH3NH3Pb(I1–xBrx)3/TiO2/FTO/glass photovoltaic devices. The room-temperature spectra show exponential band tails with a sharp onset characterized by low Urbach energies (Eu) over the full halide composition space. The Urbach energies are 15–23 meV, lower than those for most semiconductors with similar bandgaps (especially with Eg > 1.9 eV). Intentional aging of CH3NH3Pb(I1–xBrx)3 for up to 2300 h, reveals no change in Eu, despite the appearance of the PbI2 phase due to decomposition, and confirms a high degree of crystal ordering. Moreover, sub-bandgap EQE measurements reveal an extended band of sub-bandgap electronic states that can be fit with one or two point defects for pure CH3NH3PbI3 or mixed CH3NH3Pb(I1–xBrx)3 compositions, respectively. Finally, the study provides experimental evidence of defect states close to the midgap that could impact photocarrier recombination and energy conversion efficiency in higher bandgap CH3NH3Pb(I1–xBrx)3 alloys.},
doi = {10.1021/acsenergylett.6b00727},
journal = {ACS Energy Letters},
number = 3,
volume = 2,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2017},
month = {Wed Feb 15 00:00:00 EST 2017}
}

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  • Two-dimensional (2D) hybrid halide perovskites come as a family (B) 2(A) n-1PbnX 3n+1 (B and A= cations; X= halide). These perovskites are promising semiconductors for solar cells and optoelectronic applications. Among the fascinating properties of these materials is white-light emission, which has been mostly observed in single-layered 2D lead bromide or chloride systems (n = 1), where the broad emission comes from the transient photoexcited states generated by self-trapped excitons (STEs) from structural distortion. Here we report a multilayered 2D perovskite (n = 3) exhibiting a tunable white-light emission. Ethylammonium (EA+) can stabilize the 2D perovskite structure in EA 4Pbmore » 3Br 10–xCl x (x = 0, 2, 4, 6, 8, 9.5, and 10) with EA + being both the A and B cations in this system. Because of the larger size of EA, these materials show a high distortion level in their inorganic structures, with EA4Pb3Cl10 having a much larger distortion than that of EA 4Pb 3Br 10, which results in broadband white-light emission of EA 4Pb 3Cl 10 in contrast to narrow blue emission of EA4Pb3Br10. The average lifetime of the series decreases gradually from the Cl end to the Br end, indicating that the larger distortion also prolongs the lifetime (more STE states). The band gap of EA 4Pb 3Br 10–xCl x ranges from 3.45 eV (x = 10) to 2.75 eV (x = 0), following Vegard’s law. First-principles density functional theory calculations (DFT) show that both EA 4Pb 3Cl 10 and EA 4Pb 3Br 10 are direct band gap semiconductors. The color rendering index (CRI) of the series improves from 66 (EA 4Pb 3Cl 10) to 83 (EA 4Pb 3Br 0.5Cl 9.5), displaying high tunability and versatility of the title compounds.« less
  • Perovskite-type CH{sub 3}NH{sub 3}PbI{sub 3}-based photovoltaic devices were fabricated and characterized. Doping effects of thallium (Tl), indium (In), or germanium (Ge) element on the photovoltaic properties and surface structures of the perovskite phase were investigated. The open circuit voltage increased by Ge addition, and fill factors were improved by adding a small amount of Ge, Tl or In. In addition, the wavelength range of incident photon conversion efficiencies was expanded by the Tl addition.
  • We present the new homologous series (C(NH2)3)(CH3NH3)nPbnI3n+1 (n = 1, 2, 3) of layered 2D perovskites. Structural characterization by single-crystal X-ray diffraction reveals that these compounds adopt an unprecedented structure type, which is stabilized by the alternating ordering of the guanidinium and methylammonium cations in the interlayer space (ACI). Compared to the more common Ruddlesden–Popper (RP) 2D perovskites, the ACI perovskites have a different stacking motif and adopt a higher crystal symmetry. The higher symmetry of the ACI perovskites is expressed in their physical properties, which show a characteristic decrease of the bandgap with respect to their RP perovskite counterpartsmore » with the same perovskite layer thickness (n). The compounds show a monotonic decrease in the optical gap as n increases: Eg = 2.27 eV for n = 1 to Eg = 1.99 eV for n = 2 and Eg = 1.73 eV for n = 3, which show slightly narrower gaps compared to the corresponding RP perovskites. First-principles theoretical electronic structure calculations confirm the experimental optical gap trends suggesting that the ACI perovskites are direct bandgap semiconductors with wide valence and conduction bandwidths. To assess the potential of the ACI perovskites toward solar cell applications, we studied the (C(NH2)3)(CH3NH3)3Pb3I10 (n = 3) compound. Compact thin films from the (C(NH2)3)(CH3NH3)3Pb3I10 compound with excellent surface coverage can be obtained from the antisolvent dripping method. Planar photovoltaic devices from optimized ACI perovskite films yield a power-conversion-efficiency of 7.26% with a high open-circuit voltage of ~1 V and a striking fill factor of ~80%.« less
  • We report the synthesis of CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) (X=Cl and I) single crystals via a stepwise temperature control approach. High-quality CH{sub 3}NH{sub 3}Pb(Br{sub 3−y}X{sub y}) crystals with a tunable bandgap from 1.92 eV to 2.53 eV have been prepared successfully in this way. And further experiments revealed the influence of halogen content and preparation temperature on the structural and optical properties of these crystals. It is observed that chlorine can lower the critical nucleation energy, which results in crystallizing at lower temperature with the chlorine content increasing, while the nucleation energy increases slowly with increasing iodine content. Moreover,more » in contrast to Frank–van der Merwe growth with low heating rate, high heating rate leads to a mass of small size single crystals and Stranski-Krastanov growth. The single crystals with tunable band gap and impressive characteristics enable us to fabricate high performance photodetectors for different wavelengths.« less
  • Here, we carried out calculations based on density functional theory to investigate the electronic, vibrational, and dielectric properties of mixed halide perovskites CH 3NH 3AI 3–xCl x with A = Pb and Sn. Computed free energies indicated that Cl mixed systems may be formed only for Cl concentrations not exceeding 10 19 cm –3, and phonon calculations showed that the disorder induced in the host lattice by the presence of a smaller halogen is responsible for mechanical instabilities. However, we found that the presence of chloride may be beneficial to the electronic properties of the perovskites. Chloride anions cause themore » organic cations to be displaced from the center of the cage; such a displacement induces preferential orientations of the cation dipole, which in turn are responsible for notable changes in the dielectric properties of the material and possibly for the formation of local ferroelectric domains. The latter are instrumental in separating electron hole pairs and hence in contributing to long charge-carrier diffusion lengths, in spite of polarons being more likely formed in mixed perovksites than in CH 3NH 3AI 3.« less