Towards Highly Efficient Cesium Titanium Halide Based Lead-Free Double Perovskites Solar Cell by Optimizing the Interface Layers

Abstract

Lead halide perovskites are the most promising compared to the other recently discovered photovoltaic materials, but despite their enormous potential, these materials are facing some serious concerns regarding lead-based toxicity. Among many lead-free perovskites, the vacancy-ordered double perovskite cesium titanium halide family (Cs2TiX6, X = Cl, Br, I) is very popular and heavily investigated and reported on. The main objective of this study is to design and compare an efficient cesium titanium halide-based solar cell that can be used as an alternative to lead-based perovskite solar cells. For efficient photovoltaic requirements, the hole-transport layer and electron-transport layer materials such as PEDOT:PSS and Nb2O5 are selected, as these are the commonly reported materials and electronically compatible with the cesium titanium halide family. For the active layer, cesium titanium halide family members such as Cs2TiCl6, Cs2TiBr6, and Cs2TiI6 are reported here for the devices ITO/Nb2O5/Cs2TiI6/PEDOT:PSS/Au, ITO/Nb2O5/Cs2TiBr6/PEDOT:PSS/Au, and ITO/Nb2O5/Cs2TiCl6/PEDOT:PSS/Au, respectively. To determine the most efficient photovoltaic response, all the layers (PEDOT:PSS, Nb2O5, and active perovskite layer) of each device are optimized concerning thickness as well as doping density, and then each optimized device was systematically investigated for its photovoltaic responses through simulation and modeling. It is observed that the device ITO/Nb2O5/Cs2TiI6/PEDOT:PS/Au shows the most efficient photovoltaic response with little above 18.5% for maximum power-conversion efficiency.

Investigating the Impact of Interfacial Layers on Device Performance of Highly Stable Cs2InBiBr6 Based Double Perovskite Solar Cells

“…where, J n is the rate of electron current density; J p is the rate of hole current density; G is carrier generation; R is carrier recombination; x is the function of position. Charge transport equations [11] :…”

“…Poisson equation [ 11 ] : $$$$\begin{equation}\frac{{{{\mathrm{d}}}^2\phi \left( {\mathrm{x}} \right)}}{{{\mathrm{dx}}^2}} = \frac{{\mathrm{q}}}{{{\epsilon }_{\mathrm{o}}{\epsilon }_{\mathrm{r}}}} \left( {p\left( {\mathrm{x}} \right) - {\mathrm{n}}\left( {\mathrm{x}} \right) + {N}_{\mathrm{D}} - {N}_{\mathrm{A}} + {\rho }_{\mathrm{P}} - {\rho }_n} \right)\end{equation}$$$$where, ϕ is electrical potential; q is electric charge constant; ε o is absolute dielectric constant; $${\epsilon }_r$$ is relative dielectric constant; $${N}_D$$ is donor doping density; N A is acceptor doping density; ρ P is hole density distribution; ρ n is electron density distribution; p (x) and n (x) are hole and electron density distribution as a function of the thickness (x).…”

“…Continuity equations [ 11 ] : $$$$\begin{equation}\frac{{d{J}_n}}{{d{\mathrm{x}}}} = G - R\end{equation}$$$$ $$$$\begin{equation}\frac{{{\mathrm{dJ}}_{\mathrm{p}}}}{{{\mathrm{dx}}}} = {\mathrm{G}} - {\mathrm{R}}\end{equation}$$$$where, J n is the rate of electron current density; J p is the rate of hole current density; G is carrier generation; R is carrier recombination; x is the function of position.…”

“…Charge transport equations [ 11 ] : $$$$\begin{equation}{\mathrm{J}} = {{\mathrm{J}}}_{\mathrm{n}} + {{\mathrm{J}}}_{\mathrm{p}}\end{equation}$$$$ $$$$\begin{equation}{{\mathrm{J}}}_{\mathrm{n}} = {{\mathrm{D}}}_{\mathrm{n}}\frac{{{\mathrm{dn}}}}{{{\mathrm{dx}}}} + {{{\mu}}}_{\mathrm{n}}{\mathrm{n}}\frac{{{\mathrm{d}}\phi }}{{{\mathrm{dx}}}}\end{equation}$$$$ $$$$\begin{equation}{{\mathrm{J}}}_{\mathrm{p}} = - {{\mathrm{D}}}_{\mathrm{p}}\ \frac{{{\mathrm{dp}}}}{{{\mathrm{dx}}}} + {{{\mu}}}_{\mathrm{p}}{\mathrm{p}}\frac{{{\mathrm{d}}\phi }}{{{\mathrm{dx}}}}\end{equation}$$$$where, μ n and μ p are the electron and hole mobility; D n and D p are the electron and hole diffusion coefficient.…”

“…Absorption coefficient equation [ 11 ] : $$$$\begin{equation}{\mathrm{\alpha}}\left( {{\lambda}} \right) = \left( {{\mathrm{A}} + \frac{{\mathrm{B}}}{{{\mathrm{hv}}}}} \right)\sqrt {{\mathrm{hv}} - {{\mathrm{E}}}_{\mathrm{g}}} \end{equation}$$$$where, A and B are arbitrary constants; h is Plank's constant; v is the optical frequency of photons; E g is the energy bandgap.…”