Efficiency of MAPbI₃-Based Planar Solar Cell Analyzed by Its Thickness-Dependent Exciton Formation, Morphology, and...

In spite of the impressive progresses regarding perovskite-type solar cells, a clear understanding about underlying mechanisms therein is still sparse, especially because of the absence of spatially resolved device characteristics which should be linked to exciton formation efficiency, morphology, and crystallinity being estimated as functions of positions within active layers. Here, the planar CH₃NH₃PbI₃ (MAPbI₃) perovskite solar cells (PeSCs) with ZnO as the electron-transporting layer (ETL) were fabricated. By varying the wide range of MAPbI₃ active-layer thickness, we estimate their device parameters and external quantum efficiencies in addition to internal absorption spectra (Q) by means of the transfer matrix method. Furthermore, the spectrally and spatially resolved internal quantum efficiencies (IQEs) as a function of the active-layer thickness within PeSCs were calculated, and the relationship between IQE and device parameters extracted from the current-voltage ( J- V) behaviors was discussed. It was found that the PeSC with MAPbI₃ film thickness around 303 nm has a relatively high IQE and PCE, indicating that there is more power loss of PeSCs when the thickness of the MAPbI₃ layer is either less or more than about 300 nm. Furthermore, time-resolved photoluminescence together with the thickness-dependent morphology and crystallinity of the MAPbI₃ film demonstrate that there are two power loss processes in the fabricated PeSCs: one at the ZnO/MAPbI₃ interface and the other in bulk. The present research is beneficial for further understanding of the fundamental physics for the PeSCs based on the ZnO ETL.