Design and analysis of lead-free perovskite-CZTSSe based tandem solar cell

Lead-free perovskite (LFP) materials are leading the photovoltaic (PV) market due to their nontoxic nature and good optoelectronic properties. It also increases the reliability and stability of perovskite solar cells (PSC). However, the performance of such materials is not upto the mark due to some inherent losses. Therefore, in this paper, the concept of a two-terminal monolithic tandem solar cell is utilized to mitigate the non-absorbed photon loss of the lead-free wide bandgap (1.8 eV) halide (WBH) PSC. For efficient absorption of top cell filtered spectrum, bottom cell has been designed with CZTSSe (1.1 eV) as active layer and tin (II) sulfide (Sn2S3) as back surface layer. Both LFP based top cell and CZTSSe based bottom cell have been analyzed under standalone conditions. Thereafter, to analyse the tandem configuration top cell is illuminated with AM1.5 G spectrum while for the bottom cell the unabsorbed spectrum by top cell has been used. To account for the mandate requirement of tandem cell designing current matching approach is utilized and LFP-CZTSSe tandem solar cell has been designed to deliver an efficiency of 16.6%. The obtained result shows the best current matching condition at 380 nm thick LFP and 550 nm thick CZTSSe, respectively, with a short circuit current density (JSC) of 14.9 mA/cm2. The final tandem device showed the power conversion efficiency of 16.6% with an open-circuit voltage (VOC) of 1.7 V. The obtained conversion efficiency is higher compared to till date experimental standalone conversion efficiency of LFP solar cells. Therefore, the proposed LFP-CZTSSe tandem solar cell would be a strong candidate in the PV industry delivering high efficiency at a cheap cost.