code: def calc_power_density(self):
          
          if self.bandgap == 0:
              solar_flux = units.Quantity(0., "1/(m2*s)")
          else:
              solar_flux = uibei(2, self.bandgap, self.temp_sun, 0)
          power_density = self.bandgap * solar_flux
  
          return power_density.to("W/m^2")
docs: Solar cell power density
  
          The output power density is calculated according to a slight modification of Shockley & Queisser's :cite:`10.1063/1.1736034` Eq. 2.4. This method returns values of type :class:`astropy.units.Quantity` with units of [W m^-2].