Using the TMM solver to calculate the reflection of a multilayered ARC

import matplotlib.pyplot as plt
import numpy as np
from solcore.solar_cell import Layer
from solcore.absorption_calculator import calculate_rat, OptiStack
from solcore import material, si

wl = np.linspace(300, 1900, 1000)

MgF2 = material("MgF2")()
HfO2 = material("HfO2")()
ZnS = material("ZnScub")()
AlInP = material("AlInP")(Al=0.52)
GaInP = material("GaInP")(In=0.49)

stack = OptiStack([
    Layer(si('141nm'), material=MgF2),
    Layer(si('82nm'), material=HfO2),
    Layer(si('70nm'), material=ZnS),
    Layer(si('25nm'), material=AlInP),
], substrate=GaInP, no_back_reflection=False)

angles = np.linspace(0, 80, 10)
RAT_angles = np.zeros((len(angles), 3, len(wl)))

print("Calculate RAT:")
for i, theta in enumerate(angles):
    print("Calculating at angle: %4.1f deg" % theta)
    # Calculate RAT data...
    rat_data = calculate_rat(stack, angle=theta, wavelength=wl,
                             no_back_reflection=False)

    RAT_angles[i] = [rat_data["R"], rat_data["A"], rat_data["T"]]

colors = plt.cm.jet(np.linspace(1, 0, len(RAT_angles)))

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(10, 4))

for i, RAT in enumerate(RAT_angles):
    if i == 0:
        ax1.plot(wl, RAT[0] * 100, ls="-", color=colors[i], label="R")
        ax1.plot(wl, (RAT[1] + RAT[2]) * 100, ls="--", color=colors[i], label="A+T")

    else:
        ax1.plot(wl, RAT[0] * 100, ls="-", color=colors[i])
        ax1.plot(wl, (RAT[1] + RAT[2]) * 100, ls="--", color=colors[i])

    ax2.plot(wl, RAT[1]*100, color=colors[i], label="%4.1f$^\circ$" % angles[i])

ax1.set_ylim([0, 100])
ax1.set_xlim([300, 1800])
ax1.set_xlabel("Wavelength (nm)")
ax1.set_ylabel("Reflection and transmission into structure (%)")
ax1.legend(loc=5)

ax2.set_ylim([0, 100])
ax2.set_xlim([300, 1800])
ax2.set_xlabel("Wavelength (nm)")
ax2.set_ylabel("Absorption in surface layers (%)")
ax2.legend(loc=5)

plt.tight_layout()
plt.show()