Effects of Potassium Doping on the Active Layer of Inverse-Structured Perovskite Solar Cells.

In this report, solar cell characteristics were evaluated by doping the active layer CH3NH3PbI3 (MAPbI3) with 3.0 vol% and 6.0 vol% of potassium ion (KI) in an inverse-structured perovskite solar cells (PSCs). The Tauc plots of the absorbance characteristics and the ionization potential characteristics show that the top end of the valence band shifted by 0.21 eV in the shallow direction from -5.34 eV to -5.13 eV, and the en-ergy band gap decreased from 1.530 eV to 1.525 eV. Also, the XRD mea-surements show that the lattice constant decreased from 8.96 & ANGS; to 8.93 & ANGS; when KI was doped. The decrease in the lattice constant indicates that a part of the A site is replaced from methylammonium ion (MAI) to KI. In the J-V characteristics of the solar cell, the mean value of Jsc improved from 7.0 mA/cm2 without KI to 8.8 mA/cm2 with 3.0 vol% of KI doped and to 10.2 mA/cm2 with 6.0 vol% of KI doped. As a result, the mean value of power-conversion efficiency (PCE) without KI was 3.5%, but the mean value of PCE improved to 5.2% with 3.0 vol% of KI doped and to 4.5% with 6.0 vol% of KI doped. Thus, it has shown that it is effective to dope KI to MAIPBI3, which serves as the active layer, even in the inverse -structured PSCs.