Unveiling architectural and optoelectronic synergies in lead-free perovskite/perovskite/kesterite triple-junction monolithic tandem solar cells

TL;DR

This work presents two lead-free monolithic tandem architectures using tin-based perovskites (KSnI3, FASnI3) and a kesterite absorber (ACZTSe) to achieve high-efficiency, environmentally friendly photovoltaics. By coupling rigorous optical-electrical simulations (FDTD and FEM) with hierarchical layer- and interface- optimization under current-matching constraints, the authors demonstrate a 1-J KSnI3 device reaching 16.28% and sequentially escalate to 27.29% for a 2-J tandem and 30.69% for a 3-J tandem. The results underscore the viability of earth-abundant, non-toxic absorbers in high-performance monolithic tandems and provide detailed design guidelines for absorber thicknesses, doping, and tunnel-junction engineering. The study highlights the practical potential of lead-free hybrids for sustainable, scalable photovoltaic technologies, offering a path toward reduced toxicity without sacrificing efficiency.

Abstract

The widespread use of lead-based materials in tandem solar cells raises critical environmental and health concerns due to their inherent toxicity and risk of contamination. To address this challenge, we focused on lead-free tandem architectures based on non-toxic, environmentally benign materials such as tin-based perovskites and kesterites, which are essential for advancing sustainable photovoltaic technologies. In this study, we present the proposition, design, and optimization of two distinct lead-free monolithic tandem solar cell architectures - an all-perovskite dual-junction device employing potassium tin iodide (KSnI3) and formamidinium tin triiodide (FASnI3) as absorbers for the top and bottom subcells, respectively, and a triple-junction monolithic tandem structure incorporating KSnI3, FASnI3, and Ag-doped copper zinc tin selenide (ACZTSe) as absorbers for the top, middle, and bottom subcells, respectively. We simulated the optical and electrical characteristics of these devices using the finite-difference time-domain and finite element methods, explicitly considering radiative, non-radiative, and surface recombination mechanisms. The optimized all-perovskite dual-junction solar cell achieved a power conversion efficiency (PCE) of 27.3%, with short-circuit current density (Jsc) of 14.74 mA/cm2, open-circuit voltage (Voc) of 2.227 V, and fill factor (FF) of 83.14%. Conversely, the optimized triple-junction hybrid perovskite-kesterite architecture secured an elevated PCE of 30.69%, along with Jsc of 13.184 mA/cm2, Voc of 2.766 V, and FF of 84.18%. These findings reveal the strong potential of lead-free perovskite and kesterite material based absorbers in promoting high-performance hybrid tandem solar cells, highlighting their importance in advancing sustainable and efficient photovoltaic technologies.

Figures (24)

• Figure 1: Device schematics of simulated modeled structures featuring: (a) 1-J KSnI3, (b) 1-J FASnI3, (c) 2-J monolithic KSnI3/FASnI3 tandem, and (d) 3-J monolithic KSnI3/FASnI3/ACZTSe tandem solar cells.
• Figure 2: Sequential optimization of the modeled architectures from single junction cells to triple junction tandem cells.
• Figure 3: (a) Impact on PCE ($\eta$) of the 1-J KSnI3 solar cell corresponding to the absorber thickness variation, presented for the final KSnI3 thickness iterative sweep. (b) Influence of MgF2 ARC thickness on PCE. Contour plots of key performance metrics (c) $\eta$, (d) Jsc, (e) Voc, and (f) FF as functions of ETL (TiO2) and HTL (CuSCN) thicknesses after final parametric sweeping in single junction KSnI3 cell.
• Figure 4: (a) Impact on PCE ($\eta$) through altering KSnI3, ETL, and HTL thickness under different configurations. (b) Spatial carrier generation rate profile, G, highlighting the regions of maximum generation. (c) Absorbed power P$_{abs}$ towards the illumination of sunlight in the Y direction. (d) Spectral power absorption of different layers 1-J KSnI3 cell versus photon wavelength corresponding to AM 1.5G solar spectrum. (e) Comparison between J-V and P-V plot for incorporating Au and ITO as BCL. (f) Internal and external quantum efficiency (IQE, EQE) along with cumulative Jsc vs photon wavelength of the optimized 1-J KSnI3 cell.
• Figure 5: Impact on PCE ($\eta$) through altering (a) FASnI$_3$ absorber thickness and (b) FASnI$_3$ acceptor doping density N$_A$. Contour plot featuring performance matrices (c) $\eta$, (d) Jsc, (e) Voc, and (f) FF corresponding to variation of donor doping density, N$_D$ of TiO2 ETL and acceptor doping density, N$_A$ of CuSCN HTL for 1-J FASnI$_3$ cell. (g) Impact of MgF2 ARC and Spiro-OMeTAD thickness on PCE of 1-J FASnI$_3$ cell. (h) Comparison between featuring normalized power absorption, reflection, and transmission corresponding to photon wavelength (i) J-V and $\eta$-V response for 1-J FASnI3 with ITO and Au configurations.