Synthesis, Characterization, and Photoelectric and Electrochemical Behavior of (CH₃NH₃)₂Zn_1-CoBr₄ Perovskites

We report the synthesis, characterization, and photoelectric and electrochemical properties of (CH₃NH₃)₂Zn_1-CoBr₄ (x = 0.0, 0.3, 0.5, 0.7, and 1.0) samples. X-ray powder and single-crystal diffraction confirm the formation of solid solution across the entire range. Additionally, as the cobalt concentration increases, the crystallinity of the samples decreases, as indicated by the powder diffraction patterns. All samples remain stable up to 560 K, beyond which they decompose into CH₃NH₃Br and the respective bromide. The semiconductor behavior of the compounds is confirmed through optical absorption measurements, and band gap values are determined by using the Tauc method from diffuse reflectance spectra. Raman spectroscopy reveals a slight redshift in all vibration modes with increasing cobalt content. Finally, photovoltaic measurements on solar cells constructed with (MA)₂CoBr₄ perovskite exhibit modest performance, and electrochemical measurements indicate that the compound with the composition (MA)₂Zn_0.3Co_0.7Br₄ exhibits the highest current for electrochemical water reduction during oxygen evolution.