Metal composition influences optoelectronic quality in mixed-metal lead–tin triiodide perovskite solar absorbers

Klug, Matthew T; Milot, Rebecca L.; Patel, Jay B; Green, Thomas; Sansom, Harry C.; Farrar, Michael D.; Ramadan, Alexandra J.; Martani, Samuele; Wang, Zhiping; Wenger, Bernard; Ball, James M; Langshaw, Liam; Petrozza, Annamaria; Johnston, Michael B; Herz, Laura M; Snaith, Henry J

doi:10.1039/D0EE00132E

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Metal composition influences optoelectronic quality in mixed-metal lead–tin triiodide perovskite solar absorbers

Author(s): Matthew T. Klug ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Rebecca L. Milot ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Jay B. Patel ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Thomas Green ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Harry C. Sansom ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Michael D. Farrar ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Alexandra J. Ramadan ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Samuele Martani ⁶ ^, ⁷ ^, ⁸ ^, ⁹ , Zhiping Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Bernard Wenger ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , James M. Ball ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Liam Langshaw ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Annamaria Petrozza ⁶ ^, ⁷ ^, ⁸ ^, ⁹ , Michael B. Johnston ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Laura M. Herz ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Henry J. Snaith ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2020

Journal: Energy & Environmental Science

Publisher: Royal Society of Chemistry (RSC)

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Abstract

By correlating photovoltaic and material properties with metal content, we identify compositional ranges of low and high optoelectronic quality in (FA _0.83Cs _0.17)(Pb _1−ySn _y)I ₃ perovskites.

Abstract

Current designs for all-perovskite multi-junction solar cells require mixed-metal Pb–Sn compositions to achieve narrower band gaps than are possible with their neat Pb counterparts. The lower band gap range achievable with mixed-metal Pb–Sn perovskites also encompasses the 1.3 to 1.4 eV range that is theoretically ideal for maximising the efficiency of single-junction devices. Here we examine the optoelectronic quality and photovoltaic performance of the ((HC(NH ₂) ₂) _0.83Cs _0.17)(Pb _1−ySn _y)I ₃ family of perovskite materials across the full range of achievable band gaps by substituting between 0.001% and 70% of the Pb content with Sn. We reveal that a compositional range of “defectiveness” exists when Sn comprises between 0.5% and 20% of the metal content, but that the optoelectronic quality is restored for Sn content between 30–50%. When only 1% of Pb content is replaced by Sn, we find that photoconductivity, photoluminescence lifetime, and photoluminescence quantum efficiency are reduced by at least an order of magnitude, which reveals that a small concentration of Sn incorporation produces trap sites that promote non-radiative recombination in the material and limit photovoltaic performance. While these observations suggest that band gaps between 1.35 and 1.5 eV are unlikely to be useful for optoelectronic applications without countermeasures to improve material quality, highly efficient narrower band gap absorber materials are possible at or below 1.33 eV. Through optimising single-junction photovoltaic devices with Sn compositions of 30% and 50%, we respectively demonstrate a 17.6% efficient solar cell with an ideal single-junction band gap of 1.33 eV and an 18.1% efficient low band gap device suitable for the bottom absorber in all-perovskite multi-junction cells.

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The Long-Wavelength Edge of Photographic Sensitivity and of the Electronic Absorption of Solids

Franz Urbach (1953)

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Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties.

Constantinos Stoumpos, Christos Malliakas, Mercouri Kanatzidis (2013)

A broad organic-inorganic series of hybrid metal iodide perovskites with the general formulation AMI3, where A is the methylammonium (CH3NH3(+)) or formamidinium (HC(NH2)2(+)) cation and M is Sn (1 and 2) or Pb (3 and 4) are reported. The compounds have been prepared through a variety of synthetic approaches, and the nature of the resulting materials is discussed in terms of their thermal stability and optical and electronic properties. We find that the chemical and physical properties of these materials strongly depend on the preparation method. Single crystal X-ray diffraction analysis of 1-4 classifies the compounds in the perovskite structural family. Structural phase transitions were observed and investigated by temperature-dependent single crystal X-ray diffraction in the 100-400 K range. The charge transport properties of the materials are discussed in conjunction with diffuse reflectance studies in the mid-IR region that display characteristic absorption features. Temperature-dependent studies show a strong dependence of the resistivity as a function of the crystal structure. Optical absorption measurements indicate that 1-4 behave as direct-gap semiconductors with energy band gaps distributed in the range of 1.25-1.75 eV. The compounds exhibit an intense near-IR photoluminescence (PL) emission in the 700-1000 nm range (1.1-1.7 eV) at room temperature. We show that solid solutions between the Sn and Pb compounds are readily accessible throughout the composition range. The optical properties such as energy band gap, emission intensity, and wavelength can be readily controlled as we show for the isostructural series of solid solutions CH3NH3Sn(1-x)Pb(x)I3 (5). The charge transport type in these materials was characterized by Seebeck coefficient and Hall-effect measurements. The compounds behave as p- or n-type semiconductors depending on the preparation method. The samples with the lowest carrier concentration are prepared from solution and are n-type; p-type samples can be obtained through solid state reactions exposed in air in a controllable manner. In the case of Sn compounds, there is a facile tendency toward oxidation which causes the materials to be doped with Sn(4+) and thus behave as p-type semiconductors displaying metal-like conductivity. The compounds appear to possess very high estimated electron and hole mobilities that exceed 2000 cm(2)/(V s) and 300 cm(2)/(V s), respectively, as shown in the case of CH3NH3SnI3 (1). We also compare the properties of the title hybrid materials with those of the "all-inorganic" CsSnI3 and CsPbI3 prepared using identical synthetic methods.