Defect Investigation in Perovskite Solar Cells by the Charge Based Deep Level Transient Spectroscopy (Q-DLTS)

Among the recent progress in solar cells, the use of the organic-inorganic hybrid perovskites as absorbers has been demonstrated to provide higher efficiency and stability for applications in photovoltaics. The improvement of the cell performance with a power conversion efficiency reaching 20% is thought to be linked to their optoelectronic properties of perovskites: strong optical absorption, high carrier mobility and diffusion length. However, from the defect point of view, the complex structure of the materials is prone to formation of defects, which enables charge carrier trapping, and therefore can impact on the long term stability and electrical property of the solar cells. In this work, we investigated defects in CH ₃ NH ₃ PbI ₃ perovskite solar cells by the charge based Deep Level Transient Spectroscopy (Q-DLTS), which provides trap parameters including activation energy, capture cross section and trap density of different defect levels. A large trap distribution versus energy with a maximum centered at 0.45 eV was found in the studied devices. On the other hand, a strong dependency of the Q-DLTS spectra on the polarity of the sample suggests that measured traps are likely linked to the interface between perovskite and transport layers. Understanding the structure-property relationships of perovskites may help to improve the design and thus, the performance of hybrid organic-inorganic solar cells.