Perovskite-CIGS Monolithic Tandem Solar Cells with 29.7% Efficiency: A Numerical Study

Tandem solar cells have higher efficiency than single-junction devices owing to their wide photon absorption range. A wide band gap (Eg) absorber absorbs the higher-energy photons in the top cell. In contrast, a comparatively low band gap absorber material is utilized in the bottom cell to absorb the filtered low-energy photons. Consequently, thermalization and transparent energy losses are overshadowed by the top subcell (Topsc) and the bottom subcell (Bottomsc), respectively. However, to achieve the best efficiency from a tandem design, the choice of active material in the Topsc and the Bottomsc plays an important role. Therefore, in this proposed study, a tandem solar cell comprising a perovskite (Eg 1.68 eV)-based top cell and a copper indium gallium selenide (CIGS, Eg 1.1 eV)-based Bottomsc has been designed and analyzed. A state-of-the-art Me-4PACz ([4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid) hole transport layer (HTL) in the perovskite solar cell reported in the previous literature has been considered for the top cell, whereas a calibrated CIGS-based Bottomsc with 16.50% efficiency is designed. Both the Topsc and the Bottomsc are examined for the tandem configuration using filtered spectra and current-matching techniques. In perovskite/CIGS tandem design, an ideal tunnel recombination junction uses Me-4PACz and ITO layers. In a tandem configuration with matched current density at an absorber thickness of 347 nm for Topsc and 2.0 μm for Bottomsc, the device delivered an open-circuit voltage (VOC), current density (JSC), and fill factor (FF) of 1.92 V, 20.04 mA/cm2, and 77%, respectively, resulting in an overall power conversion efficiency (PCE) of 29.7%. The results reported in this work would be beneficial for the development of perovskite-CIGS-based monolithic tandem solar cells in the future.