Description
Date/Time: 04-04-2018 - Wednesday - 05:00 PM - 07:00 PM
Arun Kumar Mannodi Kanakkithodi1 Duyen Cao2 Nari Jeon2 Alex Martinson2 Maria Chan1

1, Argonne National Laboratory, Argonne, Illinois, United States
2, Argonne National Laboratory, Argonne, Illinois, United States

Lead halide hybrid perovskite semiconductors have emerged as attractive candidates for photovoltaic applications owing to their large absorption coefficients, easy synthesis and property tailoring via composition engineering. MAPbX3 perovskites (where MA = methylammonium and X = Br/Cl) were the subject of recent studies on the partial substitution of Pb to obtain stable mid-gap states with tunable energy level [1,2]. This paves the path towards a new class of multi-junction devices called intermediate band (IB) photovoltaics, which can theoretically surpass the Shockley-Queisser (S-Q) limit of solar conversion efficiency with additional absorption of sub-gap photons [3,4]. Density functional theory (DFT) calculations revealed that 1/8th substitution of Pb by Co in MAPbBryCl3-y (y ∈ {0-3}) perovskites (ideal parent semiconductors with band gaps between 2 eV and 2.3 eV) creates mid-gap energy states, which was experimentally confirmed via absorption and photoluminescence spectra with sub-gap absorption observed between 1.65 eV and 2 eV [1]. The lack of a second sub-gap absorption feature indicated that the mid-gap states were unfilled at the current level of substitution. This prompted the study of alternative substituents besides Co that can replace Pb in MAPbBryCl3-y with a thermodynamic penalty similar to the thermal energy, and create desirable half-filled mid-gap states. Here, we report the crystal and electronic structure changes upon substitution of Pb by several 3d transition and Group I, II, III, IV and V metals of suitable ionic sizes (based on perovskite stability tolerance and octahedral factors) in MAPbBryCl3-y systems (y ∈ {0-3}), specifically noting trends in parent band gap and substituent energy states within the band gap. Each metal substitution was studied in different charged states and charge transition energy levels were determined. We further compared formation energies of external metal substitution and various intrinsic point defects (vacancy, self-interstitial and anti-site) as a function of chemical potentials of constituent species [5], and determined the thermodynamic equilibrium growth conditions necessary for creating a stable external substitution that compensates for dominant intrinsic defects. Based on this work, promising candidates were identified as Pb-substituents in lead-based hybrid perovskites to create IB photovoltaic materials.

REFERENCES

[1] M.D. Sampson et al., J. Mater. Chem. A. 5, 3578 (2017).
[2] M.T. Klug et al., Energy & Environ. Sci. 10, 236 (2017).
[3] A. Luque et al., Nat. Photonics. 6, 146–152 (2012).
[4] A. Luque et al., Phys. Rev. Lett. 78, 5014-5017 (1997).
[5] Y. Yan et al., Springer International Publishing, Switzerland (2016).

Meeting Program
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5:00 PM–7:00 PM Apr 4, 2018

PCC North, 300 Level, Exhibit Hall C-E