(555a) Dimensionally Modified Halide Perovskites and Dichalcogenides for Thin-Film Tandem Solar Cells

Thin-film photovoltaic (PV) technologies such as CdTe and CIGS are limited by an efficiency plateau due to limiting factors such as small minority carrier lifetimes, high surface recombination rates and low dopability resulting in large V_OC-deficits compared to ideal values based on detailed-balance approach. Although many approaches are being taken to improve power conversion efficiency (PCE) of single-junction devices including novel buffer layers, dopants, bandgap grading, post-deposition treatments, etc. the improvements in performance have been limited. Here, we will present thin-film tandem PV approach for superstrate CdTe and substrates CIGS technologies using 0D-halide perovskite and 2D-transition metal dichalcogenide (TMD) materials.

Cs₂SnI₆ has a direct bandgap of 1.6 eV, and the closed-packed halide framework results in dispersed conduction and valence bands leading to low electron effective masses of 0.48m₀ for electrons and 1.32m₀ for holes. Cs₂SnI₆ exhibits electron and hole mobilities of 310 cm²V^-1s^-1 and 42 cm²V^-1s^-1, respectively, and is believed to be an ambipolar material due to formation of n-type iodide vacancies/tin interstitials or p-type cesium vacancies. Devices up to 5% PCE have been demonstrated with enhancements such as Cl, F, Rb, Ag, In doping; ZnO nanorod electron transport layer (ETL); ethylene diamine post-deposition treatments. Our recent results have shown Cs₂SnI₆ superstrate n-i-p planar devices with Zn(O,S) ETL and ethylene diamine (EDA) post-deposition treatment with PCE of 5.18%; making it a promising candidate as top-cell for CIGS tandem devices.

Although wide-bandgap halide perovskites offer promising solutions for substrate thin-film PV technologies like CIGS, novel low-bandgap stable materials are needed for a superstrate PV technology like CdTe. Here, we present a novel device design with CdTe/2D-MoTe₂ tandem devices, wherein 2D-MoTe2 exhibits a bandgap of 1.1 eV and excellent electron and hole mobilities of 110 cm²V^-1s^-1 and 426 cm²V^-1s^-1, respectively.

Here, we will present our recent analysis on Cs₂SnI₆/CIGS and CdTe/2D-MoTe₂ thin-film tandem solar cells with 2-terminal and 4-terminal architectures. Recent experimental results towards demonstration of 4-T tandem devices will also be discussed.