Analysing the effect of crystal size and structure in highly efficient CH₃NH₃PbI₃ perovskite solar cells by spatially resolved photo- and electroluminescence imaging

Abstract

CH3NH3PbI3 perovskite solar cells with a mesoporous TiO2 layer and spiro-MeOTAD as a hole transport layer (HTL) with three different CH3NH3I concentrations (0.032 M, 0.044 M and 0.063 M) were investigated. Strong variations in crystal size and morphology resulting in diversified cell efficiencies (9.2%, 16.9% and 12.3%, respectively) were observed. The physical origin of this behaviour was analysed by detailed characterization combining current-voltage curves with photo- and electroluminescence (PL and EL) imaging as well as light beam induced current measurements (LBIC). It was found that the most efficient cell shows the highest luminescence and the least efficient cell is most strongly limited by non-radiative recombination. Crystal size, morphology and distribution in the capping layer and in the porous scaffold strongly affect the non-radiative recombination. Moreover, the very non-uniform crystal structure with multiple facets, as evidenced by SEM images of the 0.032 M device, suggests the creation of a large number of grain boundaries and crystal dislocations. These defects give rise to increased trap-assisted non-radiative recombination as is confirmed by high-resolution μ-PL images. The different imaging techniques used in this study prove to be well-suited to spatially investigate and thus correlate the crystal morphology of the perovskite layer with the electrical and radiative properties of the solar cells and thus with their performance.

UV Degradation and Recovery of Perovskite Solar Cells

“…The μ-PLS and μ-LBIC mappings were performed with a photoluminescence spectroscopy setup using a confocal microscope, illuminating the samples from the glass side6667. The point-shaped excitation and detection allows for diffraction limited resolution when using an objective lens with a low numerical aperture (<0.1).…”

Multiple‐Trapping Model for the Charge Recombination Dynamics in Mesoporous‐Structured Perovskite Solar Cells

“…Accordingly,h igh excitation intensity tends to trigger high-order dynamic processes. [14,15] Meanwhile, the trap state density in bulk perovskite (CH 3 NH 3 PbI 3 )t hin films is about 10 16 cm À3 ; [16,17] therefore, the photo-generated speciesi ntroduced by sun irradiation is not abundant enough to fulfill the trap states, indicating that the trap states would play ac rucial role in charge-carrier recombination in an intrinsic perovskite layer. [14,15] Meanwhile, the trap state density in bulk perovskite (CH 3 NH 3 PbI 3 )t hin films is about 10 16 cm À3 ; [16,17] therefore, the photo-generated speciesi ntroduced by sun irradiation is not abundant enough to fulfill the trap states, indicating that the trap states would play ac rucial role in charge-carrier recombination in an intrinsic perovskite layer.…”

Wafer-scale single-crystal perovskite patterned thin films based on geometrically-confined lateral crystal growth

“…To achieve high performance in the perovskite-based devices, it is crucial to employ high-quality single-crystal perovskite thin films with minimum structural defects, such as dislocations and grain boundaries. In principle, perovskite films with larger grains have lower densities of grain boundaries; therefore, their optoelectrical properties can be closer to those of single-crystal perovskites272829. Recent efforts to obtain high-quality crystals have used a hot-casting technique to produce millimetre-scale grains of perovskites using a heated substrate to accelerate the growth of crystals in the presence of a solvent430.…”