Fabrication of planar heterojunction oxide solar cells by radio frequency magnetron sputtering

In this study, planar heterojunction oxide solar cells (PHOSC) in both (p-i-n) and (n-i-p) configurations are fabricated using the radio frequency (RF) magnetron sputtered tin oxide (SnO2), copper (II) oxide (CuO) and nickel oxide (NiO) as n-type, absorber and p-type layers, respectively. XRD analysis confirmed the formation of tetragonal SnO2, monoclinic CuO, and cubic NiO phases. The cross-sectional SEM analysis showed the columnar growth for the sputtered metal oxide layers and XPS analysis revealed the valence states of metal oxides. Optical bandgap of n-type, absorber and p-type layers were found to be 3.7, 1.2 and 3.5 eV, respectively which leads to a staircase arrangement in the energy level alignment. The fabricated device with 600 nm thickness shows power conversion efficiency (PCE) (η) of 2.3% with enhanced open-circuit voltage (Voc) = 0.75 V, short-circuit current density (Jsc) = 5.73 mA/cm2 and fill factor (FF) of about 54% for (n-i-p) configuration. Similarly for (p-i-n) configuration, (η) of 0.4% is achieved with decreased Jsc. This new strategy paves the way for easier, stable and large scale fabrication of planar oxide solar cells.