Mechanically-stacked perovskite/CIGS tandem solar cells with efficiency of 23.9% and reduced oxygen sensitivity

A perovskite/CIGS tandem configuration is an attractive and viable approach to achieve an ultra-high efficiency and cost-effective all-thin-film solar cell. In this work, we developed a semi-transparent perovskite solar cell (PSC) with a maximum efficiency of 18.1% at a bandgap of ∼1.62 eV. Combining this cell in a mechanically stacked tandem configuration with a 16.5% CIGS cell results in a tandem efficiency of 23.9%. We also present a semi-transparent high bandgap (∼1.75 eV) PSC with a champion efficiency of 16.0% that enables a tandem efficiency of 23.4%. Optical simulation predicts that a perovskite/CIGS tandem efficiency of over 30% is feasible with a high bandgap perovskite top cell. The multiple-cation perovskite absorbers enabling high tandem efficiencies in this work are found to be remarkably less sensitive towards oxygen exposure compared to the widely used CH 3 NH 3 PbI 3 (MAPbI 3 ). By combining systematic compositional tuning of perovskite materials and the simultaneous probe of terminal open-circuit voltage ( V oc ) and Photoluminence (PL) of PSCs, it is deduced that an interaction between methylamonnium (MA) cations and oxygen molecules results in an increased surface recombination rate, and this is the main driver for oxygen-induced degradation. The extraordinary device performance and stability reported in this work pave the way for ultimately realizing the commercialization of all-thin-film photovoltaic technology.