1. Testing the simulation accuracy
It is important to note that the adopted simulation setup and model parameters are already supported by experimental results on ITO/TiO2/MAPbI3/Spiro-OMeTAD where good coincidence is achieved and the discrepancy may be attributed to the series resistance and the traps density .
Figure 2 shows the J-V characterestics and QE of the simulated ITO/TiO2/MAPbI3/Spiro-OMeTAD solar cell. An efficiency of 16.56% is acheived which is almost equal to that of the experimental one, however, a slight difference is remarked especially for VOC and FF which is due principally to the interfacial traps effect and RS and RSH resistances.
2. The effect of InGaAs HTM candidate on the device optical and electrical performances
To reduce carrier recombination, the search for an effective inorganic HTM must be directed by the necessity for high carrier mobility, low cost, and a defect-free interface with the absorbing layer . In comparison to the spiro-OMeTAD, the inorganic p-type InGaAS, which has strong chemical stability, increased hole mobility, and a relatively inexpensive, is a perfect HTM . In order to evade the blurred vision about the effectiveness of this HTM material in enhancing the solar cell performance a thorough investigation is performed.
Figure 3 depicts the band diagram of the proposed structure employing InGaAs as HTM. From this figure it is shown that the proposed HTM presents good electron bloking barrier which permit a reduced recombination at the interface perovskite/InGaAs.
Figure 4 shows the reflectance and transmittance of the suggested solar cell as function of wavelength. The reflectance at incoming wavelengths of 300 nm to 1000 nm is noticeably minimized at their specified wavelengths, as can be shown. The wavelengths where the coupling of thickness and refractive index permits destructive interference between the anti-phase reflected waves from the top and bottom interfaces correspond to the minimal reflectivity.
Figure 5 depicts the absorption coefficient as function of wavelength. It is clearly shown from this figure that the absorption attains high value at λ = 450nm, this can be linked to the band gap of the absorber layer which absorbs photons in this optical range.
A solar cell's quantum efficiency is known as the amount of the number of electrons generated in the external circuit by an incident photon of a specific wavelength. Consequently, external and internal quantum efficiencies (indicated by (EQE) and (IQE), respectively, can be defined. They vary in how photons reflected from the cell are treated: all photons intruding on the cell surface are included in the EQE value, and just photons that are not reflected are included in the IQE value.
The external quantum efficiency EQE determined from electrochemical measurements at a given wavelength is calculated using the following expression:
where e is the electron charge and hc/λ the photon energy. Uncertainties are rarely mentioned, but it seems difficult to determine EQE with an accuracy better than 3% . The internal quantum efficiency (IQE) which is equal to EQE corrected for absorption and reflection losses, is expressed as follows:
Figure 6 illustrates the external and internal quantum efficiency variation across 300–1000 nm.
Although quantum efficiency should have the square form illustrated above, recombination effects limit quantum efficiency. Quantum efficiency is influenced by the same mechanisms that influence collection probability. Because blue light is absorbed extremely near to the surface, strong front surface recombination will impact the "blue" portion of the quantum efficiency. Green light is absorbed in the bulk of a solar cell, and a low diffusion length will decrease the quantum efficiency in the green section of the spectrum by reducing the collection probability from the solar cell bulk. The quantum efficiency can be defined as the probability of collecting photons caused by a single wavelength's generation profile, multiplied by the device thickness and normalized to the incident quantity of photons.
3. Impact of In mole fraction variation
In order to elucidate the impact of InGaAs HTM with different molar fraction variation on the performance of the investigated solar cell an investigation is performed. It is noted that only gap, affinity and permittivity that are varied as function of In mole fraction. Figure 7 depicts the variation of the electrical outputs as function of different InGaAs mole fraction.
From this figure, it is clearly shown that the more the In content increase the more the VOC increase, where VOC increases from 0.7 V for x=0.1 to 1.18 V for x=0.8. This enhancement is not only due to the reduced InxGa1−xAs bandgap when compared to GaAs but also to the good perovskite/InGaAs interface engineering offset. As well, the JSC and FF increase with increasing In mole fraction, this is attributed to the enhanced conductivity. The findings indicate that an In mole fraction of about 0.7 permits to reach high efficiency of 30%.
The J-V characteristics of the suggested solar cell are compared to the conventional solar cell in order to assess the influence of InGaAs HTM nominee on the solar cell electrical and optical performance. The acquired data are presented in Figure 8, where we can see that the suggested solar cell structure exhibits an obvious light absorption tendency that is superior to that of a conventional solar cell. This is mostly owing to the significant impact of the suggested construction using the InGaAs area on the solar cell's optical performance. It is noticed from this figure that the used InGaAs maintain the same VOC as Spiro OMeTAD but also improves the JSC by enhancing the carrier separation and collection mechanism through its high mobility and its narrow band gap which permit to cover wide range of light which augment the number of the photo-generated carriers.