- Layer specific absorbances for an inorganic a-Si based solar cell (Glass, 1mm, incoherent; ITO, 200nm, coherent (co); p-Si, 5nm, co; i-Si, 600nm, co; n-Si, 50nm, co; Al, 500nm, co)
Performance Evaluation of Solar Cells
The purpose of multilayer solar cells is the ability of absorbing most of the illumination within the charge generation layer.
To optimize the design of the solar cell, insight into the absorption characteristics of the device are mandatory.
The unique ability of Setfos to treat arbitrary configurations of coherent and incoherent layer structures, make this software an indispensible research tool both for organic and inorganic solar cells.
Layer Thickness Optimization
In organic solar cells, the thickness of the active layer can be optimized in order to the maximize the generated photocurrent. The below example shows the absorbance spectra as a function of the active layer thickenss in a typical P3HT:PCBM solar cell. In general, the thicker the cell, the more absorpance is observed. However, interference effects demand a numerical calculation for cell optimization.
- Left: Simulations by Setfos
- Right: Simulations by Hoppe et al. (Solar Energy Materials & Solar Cells 80, 105113, (2003))
- Surface plot (generated by HTML report) of the photocurrents of the individual subcells for estimating the optimum thicknesses for current matching.
Optimization of Tandem Solar Cells
Current-matching by adjusting the active layer thicknesses
For demonstration purposes we present here a tandem solar cell inspired by Hadipour et al. (Adv. Funct. Mater. 16 (2006)) and vary the thicknesses of the two active layers in oder to find optimum current matching conditions.
CELIV Photocurrent Simulation for Organic Solar Cells
(check the CELIV simulation example on Physical parameter extraction applications!)
Calculation of Optical Energy Flux and Absorption Profile
- Left: The optical energy flux accross the inorganic solar cell described in Figure 1. The flux is weighted by the AM1.5 solar spectrum.
- Right: The photon absorption/charge generation profile of the inorganic solar cell.
- Cross-sectional SEM image of a graded index (GRIN) ITO AR coating with modified-quintic refractive index profile after Bruggeman
Solar Cell with Rough Interfaces
Rough surfaces are known to enhance the transmission of light waves through interfaces. We tried to apply this concept to decrease the reflection at the outer Air-Glass interface and to make as adiabatic as possible to transmission from Glass to ITO. To model our device we used the effective medium approximation (EMA). The design of the outer interface is summarized through three virtual media representing the spikes of glass in air on the left/top, their equivalent mix in the center and the valley of glass at the right/bottom, respectively. On the other hand, we designed a porous layer of ITO (50% air, 50% ITO) onto which the dense should be deposited.
- Effective media approximation (EMA): For rough interfaces, virtual layers are assumed between layers A and B. Refractive indexes of these virtual layers are proper averages from refractive indexes of layers A and B after the model of Bruggeman
- Left: Layer Absorbances for unpolarized light. Notice the widening of the active layer absorbance when a rough glass surface is considered. Solid lines refer to the smooth surface case, lines with symbols represent the case with rough surfaces. As a result, the optical efficiency increases by 8%.
- Right: Spectral field square amplitude profile. Notice the soft light penetration through the Glass (layers 0-5) that results in an increased field amplitude within the active layer (7-8) in the visible range. Abscissa expressed in terms of relative position because of the very thick glass substrate.
IV characteristics of organic solar cells
The quantification of the recombination losses is possible with coupled optical-electrical calculations. Also peak-power characteristics are computed.
Also the comparison of the maximum short circuit current Isc and the measurable current at the electrodes is a good method to determine the recombination losses. In the plots below the thickness of the P3HT-PCBM layer has been varied.
Dark current
Setfos quantifies the dark current through a solar cell. Thank to a fast steady-state solver, calculate IV curves dominated by diffusion in no time.