Abstract
Mixed-organic-cation perovskite absorbers as formamidinium doped methylammonium tin iodine (text {NH}_2text {CH})_{1-{x}}(text {CH}_3text {NH}_3)_xtext {SnI}_3 (xle 1) can provide a pathway to highly efficient lead-free solar cells. Although this class of materials is known to be severely susceptible to degradation, induced among others by enhanced temperatures, humidity and illumination, an improved layer quality in view of crystal size and homogeneity is the key to diminish or even to block certain degradation channels. In this work, we present the fabrication of fully tin-based perovskites via pulsed laser deposition. The morphology is analyzed for different deposition energies and temperatures to find the optimum process window. The thin films already reveal crystalline structure at room temperature, while they are smooth and homogeneous above a critical thickness for carefully adapted deposition parameters. In contrast to the assumption that at elevated temperatures, the crystallinity is improved, and we find that the films reveal a strong organic depletion and simultaneously tin enrichment. As a measure for their suitability to be employed as photovoltaic absorbers, the band gap of the differently doped perovskites is estimated by spectroscopic ellipsometry in the range of 1.3 to 1.4 eV.
Highlights
Thin film hybrid organic–inorganic perovskite (HOIP) solar cells were identified to be a suitable alternative to conventional Si-cells, since they are cheap, scalable and fabricated from abundant materials
The most important component is the absorber layer that consists of a metal halide in perovskite structure, where metals from group IV (Ge, Sn and Pb) and organic complexes as methylammonium iodine (MAI) and formamidinium iodine (FAI) are frequently used
Whether the perovskite structure can be built despite organic deficiency is analyzed using the example of MAFASI by recording diffractograms of thin films deposited at room temperature using different energies from 80 to 200 mJ (Fig. 4), the diffractograms are dominated by the [001] -reflections of SnI2
Summary
Thin film hybrid organic–inorganic perovskite (HOIP) solar cells were identified to be a suitable alternative to conventional Si-cells, since they are cheap, scalable and fabricated from abundant materials. The most important component is the absorber layer that consists of a metal halide in perovskite structure, where metals from group IV (Ge, Sn and Pb) and organic complexes as methylammonium iodine (MAI) and formamidinium iodine (FAI) are frequently used These complexes reveal exceptional photovoltaic properties due to a balanced transport of. It was shown that with mixing FA and MA, the film morphology is improved [53], the charge carrier recombination [9] and the extent of Sn oxidation are notably reduced, and the new structure is more sensitive to water absorption [48] This compositional engineering incidentally leads to a strengthening of the thermal stability [8, 20]. The suitability of the PLD fabricated films for applications in photovoltaics is checked by evaluating the band gaps
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