Progress in tin-germanium perovskite solar cells: A review

The primary cause for concern in developing perovskite solar cells (PSCs) is the potential environmental repercussions of employing lead (Pb) as the absorber. The majority of studies hypothesised that the use of tin-based perovskite could be the key to creating environmentally and financially viable PSCs. This is because tin (Sn) and lead (Pb) are both elements in group 14 of the periodic table. Perovskite materials based on tin and lead also have nearly ideal direct band gaps, which range from 1.23 eV to 1.30 eV. Nonetheless, major challenges that may suppress the potential of Sn-based PSCs include the stability issue with low formation energy, high carrier density, and easily oxidised from Sn2+ to Sn4+ upon exposure to air. These limitations are anticipated to be vital impediments to creating a stable and effective Sn-based perovskite. Recent advances have shown that alloying with germanium (Ge) is one of the approaches to overcome stability issues and thus improve the overall efficiency of the PSCs. However, the stability and efficiency of these Ge-based PSCs are still unable to surpass those of Pb-based devices. This review covers the research interest in SnGe PSCs from the initial study to the current year by focusing on the methodology used and significant results. The output is believed to be useful in developing Pb-free PSCs using SnGe-based materials.