Tunneling-Assisted Trapping as one of the Possible Mechanisms for the Origin of Hysteresis in Perovskite Solar Cells

Perovskite solar cells (PSCs) are among the promising candidates to reach the highest efficiency among single-junction solar cells due to their band gap around 1.55 eV, strong absorption, and long charge carrier diffusion length. However, the anomalous hysteresis observed in its current-voltage (I-V) curves that creates confusion about the true efficiency has been a serious drawback for further improvement of its stable power output. Hence, understanding the origin of the I-V hysteresis is important and has been discussed widely in recent publications. Herein, the hysteresis in the I-V curves of PSCs has been studied by using a two-dimensional model employing the Silvaco Atlas software. The study was performed using planar structure cells made of fluorine-doped tin oxide glass substrate (FTO), a compact-titanium-oxide (c-TiO2) electron-transport layer, methylammonium lead triiodide (MAPbI(3)) layer, 2,2', 7,7'-tetrakis-(N, N-di-4-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) holetransport layer and gold back contact. The effect of trap-assisted charge accumulation in c-TiO2 and recombination at the c-TiO2/MAPbI(3) interface on the I-V curves is assessed. The study shows that these two processes can reproduce the hysteresis behavior as a function of the scan rate and voltage preset in PSCs. Also, this study suggests that decreasing charge trapping and recombination at the c-TiO2/MAPbI(3) interface could be important to reduce hysteresis and improve the PSC efficiency.