Characterization of as prepared and exposed Perovskitesolar cells by microscopic and spectroscopic techniques

Sammanfattning: Studying the microstructural features, optical, and electrical properties of the thin-filmperovskite solar cells (PSC) is the main objective of this thesis work. All the PSCs used in thisthesis work were prepared by spin coating assisted with gas quenching process and the samplesreceived from Interuniversity Microelectronics Centre (IMEC), Belgium.Microstructural and architectural details of the stagewise prepared PSCs were investigatedusing a Scanning Electron Microscope (SEM) - Focused Ion Beam (FIB) technique. With thereference to the given specification from IMEC, the SEM-FIB examinations of the as-preparedPSCs confirmed the presence of different layers such as hole transport layer (HTL), perovskitelayer, and electron transport layer (ETL). Further, the thickness of the perovskite layers wasmeasured and found to be 400 and 500 nm which validates the specification of the as-preparedsamples 1 and 2, respectively. The observed average grain size of the perovskite of the asprepared samples 1 and 2 are significantly different and the values are approximately 83 and169 nm, respectively. The average surface roughness values of perovskite layers (as-preparedsamples 1 and 2) and electron transport layer (as-prepared samples 3) were evaluated by atomicforce microscopy (AFM) and the values are 10, 19, and 12 nm, respectively. Furthermore, theconductive-AFM was performed to evaluate the electrical properties of the perovskite layers,and the results confirmed that the as-prepared sample 2 showed a higher mean current value of4.1 nA, than sample 1 resulted in 2.9 nA. The higher electrical performance of the as-preparedsample 2 could be correlated to the larger grain size, higher thickness, and higher surfaceroughness values of the perovskite layer.Moreover, the performance evaluation of a complete perovskite solar device with a similarconfiguration was evaluated between the as-prepared (newly fabricated) and the exposedsamples (tested under sunlight for ten weeks), and their behavior was studied. The optical andelectrical characteristics of the solar cell at the device level were examined with the help ofphotoluminescence (PL), electroluminescence (EL), and solar simulator techniques. The peakand fullwidth half maximum (FWHM) values of the PL emission spectra of the as-prepareddevice are in line with IMEC specification, whereas these values are slightly decreased for theexposed perovskite solar device. Also, during the EL examination, predominantly uniformluminescence was observed for the as-prepared device, whereas discontinuity in the emissionof electrons, and in some parts absence of luminescence-effect was observed for the exposedsolar cell. The current-voltage characteristics obtained from the solar simulator resultsconfirmed that the power conversion efficiency of the as-prepared device is at least 6 timeshigher than the exposed device. Based on the PL, EL, and PCE results it could be confirmedthat the perovskite solar cell exposed to sunlight for 10 weeks has started to degrade.