Numerical simulation of heat distribution in RGO-contacted perovskite solar cells using COMSOL
Introduction
Graphene with covalent sp2 bonds, and its derivative oxides including graphene oxide (GO) and reduced graphene oxide (RGO) has been introduced as a promising material for the back contact of solar cells (Hu et al., 2017, Rafique et al., 2019, Chowdhury et al., 2018). The high electrical and thermal conductivity, transparency, thin thickness, and flexibility makes the graphene derivatives the ideal candidates for perovskite photovoltaics. The two dimensional graphene sheet has an excellent thermal conductivity in the range of 3600–5400 W/m.K at room temperature. Such a high thermal/electrical conductivity is assigned to it’s extraordinary high electron mobility of 15,000 cm2/(V.s) (Schöche et al., 2017). Graphene has been used as the electrode in perovskite solar cells to foster the heat dissipation and reducing the perovskite’s decomposition rate (Li et al., 2016) or ion electroimmigration at high temperature (Palma et al., 2016). The RGO layer can protect the perovskite layer from moisture ingression which enhances the thermal and electrical stability of the cell by preventing the PbI2 defective surface layer. RGO layer can also enhance the heat dissipation to keep the temperature of the cell below 80 °C which is essential for the performance stability over time. Simulation analysis of heat dissipation in graphene contacted perovskite solar cells using the 1D platforms (SCAPS-1D, AMPS-1D, etc.) may not be feasible (or valid), because, solar cells are basically 3D structures and graphene is a 2D or 3D material (Hu et al., 2017, Soucase et al., 2016). Therefore, other platforms such as TCAD- Silvaco or COMSOL multiphysics are suitable for 3D simulation analysis of graphene contacted perovskite solar cells (Wu et al., 2016, Lavery et al., 2016). These 3D simulation packages are capable of solving the coupled optical-electrical-thermal (OET) problems with valid meshing boundary conditions and proper concept physics. Nevertheless, COMSOL was used mostly to map the carrier generation profile, hole and electron concentration profile or optical analysis of solar cells and (to our best of knowledge) no comprehensive simulation were presented in literature on coupled OET problems for heat and temperature mapping in perovskite cells, especially with a graphene contact. Most of such analysis were developed in semi-classical modeling approaches (Kang et al., 2019, Zhang et al., 2016). There is almost no such 3D simulation on graphene contacted solar cells not for thermal mapping nor on heat distribution analysis or heat dissipation in 3D environment. However, the heat transfer module in COMSOL enables mapping the heat and temperature across the cell and investigating the contribution of graphene thermal properties to device stability by taking into account the heat generating sources (Shao et al., 2019, Niyat and Abadi, 2018). The Heat Transfer module in COMSOL Multiphysics allows modeling the very high aspect ratio components using the highly conductive layer features such as graphene layer. For such a feature, the heat transfer equation is solved only in the tangential surface plane thus removing the need to use a very fine mesh on the high aspect ratio layers. In turn, the required memory and time for computation is reduced significantly. Paletti et al. have shown that Graphene organic solar cells can be more efficient compared to ITO contacted counterpart if the graphene’s series resistance is minimized, and it’s work function is optimized (e.g. a doped graphene or RGO) (Paletti et al., 2015).
In this paper, we investigate the optical, electrical and thermal behavior of RGO-contacted perovskite cells using the coupled modules in COMSOL multiphysics package. In particular, we present our 3D simulations of the optical generation rate, current-voltage characteristics, electric field distribution, heat flux and temperature distribution across the cell especially at the RGO/spiro junction. It was found that solar cells with RGO electrode can outperform the others in low thermal degradation rate since the heat flux and temperature distribution at the RGO/Spiro junction is significantly lower than the Au contacted cells. We have provided a coupled model of optical, electrical and thermal models for this 3D system which suits perfectly the 2D nature of a solar cell and the 3D nature of graphene (RGO) electrode.
Section snippets
Simulation and modeling
The thermal conduction in our graphene-contacted perovskite solar cell is simulated using COMSOL software package which numerically solves the partial differential equations in order to investigate the thermal transport in this hybrid structure made of graphene nanostructure and perovskite organic-inorganic layer. The 3D simulations of the optical generation, electric field distribution, recombination rate, current-voltage characteristics, thermal and heat distribution maps are all performed by
Physics and the simulation results
The most basic use of COMSOL for photovoltaic simulation requires coupling both Semiconductor and Wave Optics modules. Although the heat is transferred by conduction between the layers in the cell, the heat dissipates to ambient air from top FTO electrode or bottom RGO contact via convection. The transient state is neglected here because it takes a relatively short time to reach the steady-state where the temperature is almost stationary at any given point in the cell for a set of given
Conclusion
Our 3D simulation results combined with the models presented in semi-classical approaches in literature and the experimental data provide valuable guidelines for designing efficient and stable perovskite solar cells. Graphene derivations are promissing replacement for conventional metallic electrodes e.g. for a bifacial perovskite solar cell where graphene layer can be used for both top and bottom electrodes. We have solved a coupled optical-electrical-thermal model using COMSOL multiphysics
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This research is funded by the Foundation for Science and Technology Development of Ton Duc Thang University (FOSTECT), website: http://fostect.tdtu.edu.vn, under Grant FOSTECT.2019.18.
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