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

Abstract

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 0.21eV in the shallow direction from -5.34eV to -5.13eV, and the energy band gap decreased from 1.530eV to 1.525eV. Also, the XRD measurements show that the lattice constant decreased from 8.96Å to 8.93Å 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 J_sc improved from 7.0mA/cm² without KI to 8.8mA/cm² with 3.0 vol% of KI doped and to 10.2mA/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.