Reducing interface recombination boosts the V _oc for perovskite solar cells.

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 CH₃NH₃PbI₃ (MAPbI₃). 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.

Crystalline silicon (c-Si) solar cells featuring a high-temperature processed homojunction have dominated the photovoltaic industry for decades, with a global market share of around 93%. Integrating commercially available crystalline silicon solar cells with high-efficiency perovskite solar cells is a viable pathway to increase the power conversion efficiency, and hence achieve low levelized electricity costs for the photovoltaic systems. However, the fabrication process for this type of cell is challenging due to the many, and often conflicting, material processing requirements and limitations. Here, we present an innovative design for a monolithic perovskite/silicon tandem solar cell, featuring a mesoscopic perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell. The improved temperature tolerance of the c-Si bottom cell permits significantly increased flexibility in the design and fabrication of the perovskite cell. We demonstrate an efficiency of 22.5% (steady-state) and a V_oc of 1.75 V on a 1 cm² cell. The method developed in this work opens up new possibilities in designing, fabricating and commercialising low-cost high-efficiency perovskite/c-Si tandem solar cells.

The open‐circuit voltage (V_OC) and fill factor are key performance parameters of solar cells, and understanding the underlying mechanisms that limit these parameters in real devices is critical to their optimization. Device modeling is combined with luminescence and cell current–voltage (I–V) measurements to show that carrier transport limitations within the cell can significantly reduce the cell voltage around the maximum power point as well as, under certain conditions, at V_OC. An important consequence is that the cell terminal voltage cannot be assumed a priori to be only limited by parasitic recombination. It is demonstrated that luminescence‐based measurements can be used to reconstruct cell I–V curves with removal of any transport limitation effects, which allows the contribution of recombination, shunt resistance, and series resistance on the fill factor to be clarified. Such luminescence‐based measurements allow the contactless characterization of cells and cell precursor structures, and should prove highly valuable as a diagnostic tool for the development of new cell structures and large‐area cells.