and transport of carrier.
Variable bias of voltage, different temperature, and various illumination options
Can be used to measure concentrations and currents, J-V, C-f, C-V, and Q-V, AC characteristics and spectral response.
Calculation of single and batch values.
Final, as well as intermediate values, graphs, and other significant data, can be obtained as output and can be exported
SCAPS are arranged in several panels where the parameters can be defined by the user. The key panel is the “action panel” (Figure 1.3), in which one can set an operation point (temperature, voltage, frequency, and illumination) and the action list for calculation to be performed (J-V, C-f, C-V, Q(λ)). The running parameter (V, f, or λ) vary in the definite range in each calculation, whereas the values quantified in the operation point are for all other parameters. The user can also view the results earlier calculated directly, i.e., J-V, C-f, C-V, Q(λ), likewise, band diagrams, electric field, densities of the carrier, partial currents of recombination [36–45].
We click on the “set problem” button for the problem definition, i.e., the geometry, materials, and different characteristics of the solar cell. As depicted in Figure 1.4, the Solar Cell Definition Panel opens. In this panel, we can define up to 9 layers of structures. The back contact is the first layer; the last one is the front contact. The properties of intermediate semiconductor layers can be specified by the user. Each layer contains the following semiconductor properties, except for front and back contact:
thickness (μm),
electron affinity (eV),
band gap (eV),
dielectric permittivity (relative),
valance band effective density of states (1/cm3),
conduction band effective density of states (1/cm3),
hole thermal velocity (cm/s),
electron thermal velocity (cm/s),
acceptor shallow density (ND),
donor shallow density (ND).
Figure 1.3 Action panel of SCAPS.
Figure 1.4 Solar cell definition panel of SCAPS.
The optical absorption of the semiconductor layers can be taken from a user file. Examples of such user files are distributed with the program: Si.abs, CdS.abs, GaAs.abs, and so on. We can add other absorption files for other relevant materials.
We can also change the model for absorption, model for recombination, and apply defects to a surface in addition to these basic parameters. A panel for layer properties snapshot is illustrated in Figure 1.5.
On the panel for cell definition, which opens the panel for the properties of contacts (Figure 1.5), you can configure the contact properties by either selecting the front or back contact button.
The identification of each contact is made as follows:
electron and hole surface recombination velocities,
information about the metal work function.
Figure 1.5 Layer properties panel in SCAPS.
After loading the solar cell design with the button for set problem on SCAPS, one can set the working point. The work point specifies the parameters in a measurement that are not varied:
Temperature, T: appropriate to all measurements. In SCAPS, the only variables that have an explicit dependence on temperature are NC(T), NV(T), and thermal voltage kBT.
Voltage, V: is discarded in simulation of I-V and C-V. It is the voltage for dc-bias in simulation of C-f and simulation of QE(λ). SCAPS starts at 0V and proceeds through a series of steps at the point of operation, which we can also define.
Frequency, f: is discarded in simulation of I-V, QE(λ) and C-f. It is the frequency of the simulation of the C-V measurement.
Illumination, the illumination requirements can be further defined when simulating under illumination. The main options are: dark or light, light side choice (left/right), spectrum option. A single sun(=1000 W/m3) illumination with the “air mass.5, global” spectrum is the default, but for specialized simulations, we have a wide range of monochromatic light and spectra.
In a diode, the current at n-contact is converted from the p-contact hole current to the electron current. It implies that recombination must occur somewhere in the diode, even in the most ideal device. The user must define recombination at least at one location (in a layer or interface) somewhere. Defects are most important parameters for study of solar cells. The following parameters identify defects in SCAPS:
position of energy level in the gap,
type of defect (i.e. acceptor, donor or neutral),
thermal capture cross-section for electrons,
thermal capture cross-section for holes,
energetic distribution (single, uniform …),
defect energy level reference (above EV or below EC),
optical cross section of electrons,
capture cross section of holes,
concentration of defects.
We can select one or more of the following measurements to be simulated in the action part of the action panel (Figure 1.3): I-V, C-V, C-f and QE(λ). The start and end values of the argument and the number of steps can be adjusted if necessary.
Figure 1.6 Screenshot of energy bands panel window in SCAPS.
We select
