Improved efficiency of perovskite-silicon tandem solar cell near the matched optical absorption between the subcells

Abstract

Current matching in a tandem solar cell is significant, because in a mismatched device the lowest current generating subcell becomes the current limiting component, and overall device efficiency remains lower than that could be obtained in the current matched device. Recent reports on methyl ammonium lead iodide (MAPbI3) based thin film solar cell has drawn interest to a perovskite-silicon tandem solar cell. Therefore, we investigated such a tandem solar cell theoretically. We used a MAPbI3 based top and heterojunction with intrinsic thin layer silicon (HIT) bottom subcell. Optimization of the device structure was carried out by varying thickness of perovskite layer of top-cell from 50 to 1000 nm, while thickness of active layer of the HIT cell was kept constant, to 500 µm. Single-junction solar cell, formed with the bottom subcell had open circuit voltage (Voc) of 705.1 mV, short circuit current density (Jsc) of 28.22 mA cm−2, fill factor (FF) of 0.82 and efficiency of 16.4% under AM1.5G insolation. A relatively low thickness (150 nm) of the perovskite absorber layer was found optimum for the top-subcell to achieve best efficiency of the tandem cell, partly because of intermediate reflection at the interface between the two cells. We obtained a maximum of 20.92% efficiency of the tandem solar cell, which is higher by a factor of 1.27 from the starting HIT cell and a factor 1.47 higher from the perovskite cell efficiency. Jsc of the optimized tandem cell was 13.06 mA cm−2. This was achieved near the matching optical absorption or current-density of the component subcells. For a practical application, the device used in our investigation was without textured front surface. An ordinary HIT bottom-cell was used with lower Jsc. Therefore, with an improved HIT subcell, efficiency of the tandem cell, higher than 21% will be achievable.