Investigation of low dimensional perovskites as passivation layers in metal halide perovskite solar cells
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Low dimensional perovskites (LDPs) are currently investigated as surface passivation and charge blocking layers for stable perovskite solar cells. This master’s thesis systematically investigates the structure and optoelectronic properties of four different LDPs containing the organic ammonium cations phenethylammonium, cyclohexylethylammonium, octylammonium and hexadecylammonium, respectively. LDPs were formed in solution, on top of lead iodide films and on top of 3D perovskite films. In the latter case, ammonium cations were observed to induce the formation of thin films with very different surface morphologies. Moreover, the soaking time of the LDP precursor on top of the 3D perovskite film before spin coating resulted in very different developments of the photoluminescent quantum yield. Together, it can be concluded that the formation mechanism of LDP films is highly dependent on the ammonium cation’s nature. Exemplary for cyclohexylethylammonium, the formation mechanism was investigated via a newly established method of in-situ spectral photoluminescence measurements during annealing of the films. Two formation routes could be distinguished: Annealing the wet film directly after spin coating in the glovebox yields a pure n = 1 LDP on top of 3D perovskite. The dry route instead results first in n = 2 structures after drying at room temperature, which are then partially transformed to n = 1 LDPs upon heating. LDPs were finally applied in metal halide perovskite solar cells. Higher photoluminescence signals compared to the reference sample were observed for all LDP samples. The devices with hexadecylammonium treated absorber layer yielded higher short-circuit current densities and in consequence higher power conversion efficiencies, with a champion device achieving a stabilized efficiency of 12.6%.
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