Impact of Internal Losses on the Efficiency of All Perovskite Tandem Solar Cells: Modeling and Analysis

Hybrid halide perovskites are the most promising alternatives for photovoltaic applications due to their superior optoelectronic properties. They can also be used in tandem geometry along with other state-of-the-art solar cell technologies such as Si and CIGS. Although the efficiency has reached over 31% for Si/perovskite tandem solar cells, the manufacturing complexity and increased fabrication cost prohibit commercialization. However, a tunable bandgap in perovskites can be utilized to fabricate all-perovskite tandem solar cells with device efficiency comparable to that of Si/perovskite tandem solar cells. In this article, we have investigated all-perovskite tandem solar cell efficiency theoretically and proposed the optimum bandgap for top and bottom cells. We have demonstrated that the calculated efficiency (∼32%) from the conventional series connection is overestimated, as we have observed a very high fill factor of ∼85%. This is due to the underestimated losses at the interfaces and individual cells. We have therefore simulated the current–voltage characteristics of the tandem solar cells using an equivalent circuit model. The presence of internal resistance in each cell plays a crucial role in determining the overall device performance. The fill factor decreases to ∼80%, while the short-circuit current density and open-circuit voltages are changed only marginally. Keeping the bottom cell’s bandgap at 1.2 eV, we have achieved a maximum efficiency of 29.8% with the top cell bandgap of 1.75 eV. Further increase in the bandgap reduces the overall efficiency due to a decrease in short-circuit current density in the top cell.