**2. Simulation Method and Device Parameters**

The comprehensive simulation of the proposed lead and dopant free solar cell is performed using SCAPS 1D (version 3.3.07), as discussed above. SCAPS 1D is an excellent simulation platform, which is used to simulate the various types of one-dimension photovoltaic response. Broadly speaking, SCAPS 1D implements a set of photovoltaic models to simulate any type of photovoltaic response [19–21].

SCAPS 1D offers an interface to couple the fundamental photovoltaic equations governed by the user-defined geometry and material parameters for each layer. The fundamental equations used in these simulations are Poisson equations, device continuity equations, drift-diffusion charge transport model, recombination losses with defects model, optical absorption models, etc. These fundamental models can be further explored as:

1. Poisson model states that the one-dimension (*x*) Laplacian of the electrostatic potential field (ϕ) is equal to the ratio of total volume charge density and the permittivity

$$\frac{d^2\mathcal{D}(\mathbf{x})}{d\mathbf{x}^2} = \frac{q}{\in\_o \in\_r} \left( p(\mathbf{x}) - n(\mathbf{x}) + \mathcal{N}\_D - \mathcal{N}\_A + \rho\_p - \rho\_n \right) \tag{1}$$

where *q* is the electronic charge (1.602 × 10−<sup>19</sup> C), ε<sup>0</sup> is the permittivity of vacuumed, ε*<sup>r</sup>* is the relative semiconductor permittivity, *ND*/*NA* are the shallow donor/acceptor impurity density, *n*(*x*)/*p*(*x*) are the electron/hole density at a position *x*, and *ρn*/*ρ<sup>p</sup>* are the electron/hole density distribution.

2. The device continuity model states that change in the electron/hole current density (*Jn*/*Jp*) over a specific time as a function of position is equal to the result of generation (*G*) and the recombination (*R*) of electron/hole, respectively.

$$\frac{d\mathbf{J}\_n}{d\mathbf{x}} = \mathbf{G} - \mathbf{R} \tag{2}$$

$$\frac{dJ\_p}{d\mathbf{x}} = G - \mathbf{R} \tag{3}$$

3. The semiconductor charge transport model describes that the total electron/hole current density (*J*) is the sum of electron/hole drift and diffusion current density

$$J = J\_n + J\_p \tag{4}$$

$$J\_n = D\_n \frac{dn}{d\mathfrak{x}} + \mu\_n \ n \frac{d\varpi}{d\mathfrak{x}} \tag{5}$$

$$J\_p = D\_p \frac{dp}{d\chi} + \mu\_p \ p \frac{d\varpi}{d\chi} \tag{6}$$

where *Dn*/*Dp* are the electron/hole diffusion coefficient and *μn*/*μ<sup>p</sup>* are the electron/hole mobility, respectively.

4. For the optical absorption coefficient, SCAPS offers different options for the calculation of the absorption coefficient α (λ), but in this study, we use the following equation depending on the relation of photons (*h* is the plank constant and *ν* is the photon frequency) and perovskite (as a absorber layer) energy bandgap (*Eg*)

$$\alpha\left(\lambda\right) = \left(A + \frac{B}{h\nu}\right)\sqrt{h\nu - E\_{\mathcal{S}}}\tag{7}$$

Further detailed information about the simulation methodology can be found in our previous published paper [22]. All the materials parameters are extracted from the reported literature for BCP, PCBM, Cs2TiBr6, and NPB, which are listed in Table 1 [22–28]. Similarly, for photovoltaic characterization, the proposed device was simulated under solar illumination of air mass AM 1.5 G at 1 sun photons intensity (1000 W/m2), where ambient temperature of 300 K was used for photovoltaic simulation.

**Table 1.** Materials parameters of BCP, PCBM, Cs2TiBr6, and NPB incorporated for these simulations are listed, where each layer thickness is just reported for the first estimation, which will further improve in later stages of the simulation.



**Table 1.** *Cont.*
