Self-doped carrier as a performance limiting factor of perovskite solar cells: study on tandem-junction cells with SCAPS

Doping concentration of the absorber layer plays a vital role in the performance of perovskite solar cells, because not only it has a direct impact on the collection efficiency of the photo generated carriers, but it can also be considered as an indicator of the film quality and aging process for so-called self-doped (unintentionally doped) perovskite absorbers, where the carriers are induced from structural imperfections. To observe its influence on the efficiency of perovskite solar cell, a two-junction solar cell structure MAPbBr3/MAPbI3 is analyzed in this study, employing a novel optoelectrical simulation approach with finite-difference time-domain (FDTD) analysis and solar cell capacitance simulation (SCAPS) program. It is found that, the efficiency of the tandem cell falls from ∼22% to ∼12% as front-cell absorber film degrades from singlecrystal quality with low self-doped carrier concentration of the order of 1010cm-3, to degraded film quality with very high carrier concentration of the order of 1018cm-3. In contrast, the self-doped carrier concentration of the back-cell absorber illustrates less impact on the efficiency of the cell, especially for thicker front-cell absorber. Thus, this case study gives a simpler but novel insight into the long-term stability of the efficiency of high-performance perovskite solar cells establishing a link between the solar cell performance and the self-doped carrier concentration (doping concentration) of the absorber film