Optimization of inverted CH₃NH₃PbI₃ based perovskite solar cells by experimental design

Experimental design is not only significant for saving material, time, and cost; but also provides convenience in reducing error and interpreting results with statistical evaluations. Herein, optimization has been carried out for the absorber layer of the inverted type perovskite solar cells (PSCs) by 2³ factorial designs with the addition of center point to investigate both the individual effects of the inputs and the interaction effects between them. Experimental parameters were selected as spin speed, lead iodide (PbI₂) and methylammonium iodide (MAI) concentrations and PSCs have been prepared in ambient conditions in the configuration of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/BCP/Ag. The most effective parameter on the efficiency was found as PbI₂ concentration followed by the two important interaction effects between PbI₂-MAI concentration and PbI₂ concentration-spin speed. The best device performance was obtained by the PbI₂:MAI 1.3:1.3 M solution spin-coated at 4000 rpm as 13.97%. Open-circuit voltage (V_oc), short-circuit current density (J_sc) and fill factor (FF) values for the most efficient PSC have been found as 882 mV, 24.25 mA cm⁻² and 65.3%, respectively. Also, stability studies revealed that the sample prepared by these optimum conditions maintained 93.5% of its initial efficiency after 500 hours.