Absorption spectra of perovskites

We calculate the optical properties of a set of oxides, oxynitrides, and organometal halide cubic and layered perovskites with a bandgap in the visible part of the solar spectrum.

Ivano E. Castelli, Kristian S. Thygesen, and Karsten W. Jacobsen

Calculated optical absorption of different perovskite phases.

Journal of Materials Chemistry A, printed online.

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Key-value pairs

key	description	unit
name	Name of the structure
phase	Perovskite phase
gllbsc_dir_gap	Direct bandgap GLLB-SC	eV
gllbsc_ind_gap	Indirect bandgap GLLB-SC	eV
gllbsc_disc	Derivative discontinuity GLLB-SC	eV
eff	Calculated efficiency (thickness 1 nm)	eV
eff_max	Calculated efficiency (infinite thickness)	eV

Absorption spectrum of AgNbO3

# creates: spectrum.svg
"""Plot the absorption spectrum along the x direction for a given
perovskite"""

import matplotlib.pyplot as plt
import ase.db

# Connect to database:
c = ase.db.connect('absorption_perovskites.db')

# Select cubic symmetry containing Sn:
for n in c.select('name=AgNbO3'):
    name = n.name
    energy = n.data.energy
    im_eps_x = n.data.im_eps[0]
plt.plot(energy, im_eps_x)

plt.arrow(n.gllbsc_dir_gap,
          2,
          0.0,
          -1,
          fc="g",
          ec="g",
          head_width=0.2,
          head_length=0.3,
          head_starts_at_zero=False)

plt.text(n.gllbsc_dir_gap,
         2.1,
         'gap_d',
         rotation=90,
         horizontalalignment='center',
         verticalalignment='bottom',
         color='g')
if (n.gllbsc_dir_gap != n.gllbsc_ind_gap):
    plt.arrow(n.gllbsc_ind_gap,
              2,
              0.0,
              -1,
              fc="r",
              ec="r",
              head_width=0.2,
              head_length=0.3,
              head_starts_at_zero=False)
    plt.text(n.gllbsc_ind_gap,
             2.1,
             'gap_i',
             rotation=90,
             horizontalalignment='center',
             verticalalignment='bottom',
             color='r')

plt.ylabel('Abs. Spectrum [arb. units]')
plt.xlabel('Energy [eV]')
plt.text(7, 0.5, name)
plt.savefig('spectrum.svg')

Calculated efficiencies of the cubic phase perovskites

This script requires the perfect absorption limit:

• Download perfect absorption limit

# creates: efficiency.svg
"""Plot the efficiencies of a perovskite phase (cubic in the example
here)"""

import matplotlib.pyplot as plt
import ase.db

# Connect to database:
c = ase.db.connect('absorption_perovskites.db')

o = open('perfect_abs.txt', 'r')
lines = o.readlines()
o.close()

en = []
perf_abs = []
for line in lines:
    line = line.split()
    en.append(float(line[0]))
    perf_abs.append(float(line[2]) / 4.30E+21)

for n in c.select('phase=cubic'):
    if 'O3' in n.name:
        color = 'black'
        symb = 'o'
    if 'O2N' in n.name or 'ON2' in n.name:
        color = 'red'
        symb = 's'
    if 'O2F' in n.name:
        color = 'blue'
        symb = 'D'

    plt.plot([n.gllbsc_ind_gap, n.gllbsc_ind_gap],
             [n.eff, n.eff_max],
             '-' + symb,
             color=color)
    plt.text(n.gllbsc_ind_gap - 0.025, n.eff, n.name,
             color=color,
             fontsize=12,
             rotation=90,
             horizontalalignment='center',
             verticalalignment='bottom')

plt.plot(en, perf_abs, '--', color='green')
plt.plot(2.5, 0.32, 'o', color='black')
plt.plot(2.5, 0.29, 's', color='red')
plt.plot(2.5, 0.26, 'D', color='blue')
plt.text(2.55,
         0.32,
         'Oxides',
         color='black',
         fontsize=16,
         horizontalalignment='left',
         verticalalignment='center')
plt.text(2.55,
         0.29,
         'Oxynitrides',
         color='red',
         fontsize=16,
         horizontalalignment='left',
         verticalalignment='center')
plt.text(2.55,
         0.26,
         'Oxyfluorides',
         color='blue',
         fontsize=16,
         horizontalalignment='left',
         verticalalignment='center')
plt.text(1.3,
         0.33,
         'Cubic',
         color='black',
         fontsize=16,
         horizontalalignment='left',
         verticalalignment='center')
plt.xlim(1.2, 3.1)
plt.ylim(0, 0.35)
plt.xlabel('Bandgap [eV]', fontsize=18)
plt.ylabel('Absorbed Photons [%]', fontsize=18)
plt.xticks([1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0],
           ['1.4', '1.6', '1.8', '2.0', '2.2', '2.4', '2.6', '2.8', '3.0'],
           fontsize=16)
plt.yticks([0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3],
           ['0', '5', '10', '15', '20', '25', '30'],
           fontsize=16)
plt.savefig('efficiency.svg')