Understanding the strategies to attain the best performance of all inorganic lead‐free perovskite solar cells: Theoretical insights

Abstract

Summary Within a decade of their existence, the potential of Perovskite solar cells (PSCs) has been recognized by the research community. To date, the highest power conversion efficiency (PCE) attained by PSCs has touched the 25.8% mark. However, most of the leading PSCs have incorporation of toxic lead (Pb), posing a barrier on the market acceptability of these cells. Inorganic lead‐free PSCs are being explored extensively as clean and green energy sources. By bridging the performance gap and stability issues, the drawbacks of lead‐free PSCs can be minimized. In this work, we have optimized CsSn0.5Ge0.5I3‐based PSCs using various organic and inorganic transport layers. A comparative analysis of all the simulated cells in terms of capacitance‐voltage (C‐V) and conductance‐voltage (G‐V) characterization has been done. This work reveals the decisive role of charge transport layers (CTLs) in the determination of the built‐in potential of the cell. The impact of absorber layer thickness (with different levels of defect densities), variation of thickness of electron transport layer (ETL), and hole transport layer (HTL) on the performance of PSCs is studied. The results of study on the effect of carrier concentration on the absorber layer, ETL, and HTL (using both organic and inorganic charge transport layers) on the performance of the cell is also conducted. This study explains the role of energy band level tuning required between CTLs and the absorber layer. The role of band offset at the interface of the CTL (ETL/HTL) and perovskite layer upon charge transportation and collection mechanisms are explained in detail. We have calculated and explained the optimum Valence Band Offset and Conduction Band Offset required for a PSC to exhibit the best possible performance. In addition, we have analyzed the role of contact formation and optimum barrier height (¢B) required between HTL and back contact to obtain efficient PSC using different back contacts. Upon using similar cell configuration and different back contacts (Ni, Au, and Ag), the optimized values of (VBO, ¢B) are (0.15 eV, −0.05 eV), (0.1 eV, −0.4 eV), and (−0.15 eV, −0.51 eV), respectively.

Revealing the Role of Band Offsets on the Charge Carrier Dynamics of CsSn0.5Ge0.5I3‐Based Perovskite Solar Cell: A Theoretical Study

“…After the optimized level, for positive CBO conditions, the spike structure is formed, which acts as a barrier to the photogenerated electrons, hindering the carrier transportation and extraction. [ 20,34,35 ] Figure 2 depicts different levels of CBOs and VBOs of simulated PSCs, analyzed in this work.…”

“…After the optimized level, for positive CBO conditions, the spike structure is formed, which acts as a barrier to the photogenerated electrons, hindering the carrier transportation and extraction. [20,34,35] In this section, the CBOs are varied by keeping VBO at a constant level and at an interface defect density of 1E16 cm À3 . The activation energy (E a ) is defined as the minimum amount of extra energy required by a reacting molecule to get converted into a product.…”

Revealing the high-performance of a novel Ge-Sn-Based perovskite solar cell by employing SCAPS-1D

“…The modification of doping levels causes a change in both acceptor and donor carrier concentrations (N a and N d ), subsequently, elevating the overall carrier concentration as well as enhancing the device's conductivity. The built-in potential relies on the acceptor and donor carrier concentrations, dictated by the following equation (7) [64].…”

“…The incidence of light on the LHL highlights the pivotal role of the built-in electric field in producing and separating charge carriers. Enhanced performance of the cell corresponds directly with a stronger built-in electric field within the LHL, facilitating the efficacious extraction of charge carriers from the LHL to the contacts of charge collections [64]. Introducing dopants into the transport layer amplifies the conductivity, thereby augmenting the built-in electric field.…”

Simulation of Native Oxide‐Passivated CsSn0.5Ge0.5I3 Highly Stable Lead‐Free Inorganic Perovskite Solar Cell

“…The detailed material parameters utilized in device simulation. [39][40][41][42][43][44] Parameters/Material HTM layer (Spiro-OMeTAD) Absorption coefficient [cm À1 ] 1 0 3 10 3 10 5 10 3 10 3 concentration (electron density) in the native oxide layer does not cause any band bending or impact on efficiency as the native layer is of a high bandgap and thin layer (%5 nm). We simulated all crucial parameters of the oxide layer (such as thickness, electron affinity, and carrier density), impacting the device performance, and observed that the device efficiency does not strongly dependent on the oxide layer.…”