Enhanced optoelectronic characteristics of La-doped ZnO and its compatibility with Cs-doped MAPbI₃ perovskite absorber material

The present study investigates the structural, electrical and optical characteristics of pristine and lanthanum (La)-doped zinc oxide (ZnO) electron transport layers fabricated by the sol–gel method and their compatibility with Cs0.10MA0.90Pb(I0.9Br0.10)3 absorber layer for perovskite solar cells. All the electron transport layers were deposited under the same deposition conditions, with the only difference in La percentage in the precursor solutions, ranging from 0 to 6%. X-ray diffraction analysis demonstrated the presence of crystalline ZnO thin films and the absence of any impurity phases after La-doping. The calculated crystallite size, determined using Scherrer's equation, increased from 11.13 to 21.76 nm after the introduction of dopant. The doping with 4% La led to the decrease in the optical band gap from 3.32 eV of pristine ZnO to 3.23 eV. Scanning electron microscopy analysis revealed better morphology of perovskite / 4% La:ZnO specimen, which facilitated the absorbance and reduced the charge carrier recombination. It also exhibited superior resilience towards moisture and humidity which will eventually contribute to the development of more stable and efficient planar perovskite solar cells.