The efficiency of perovskite solar cells has surged in the past few years, while the bandgaps of current perovskite materials for record efficiencies are much larger than the optimal value, which makes the efficiency far lower than the Shockley–Queisser efficiency limit. Here we show that utilizing the below-bandgap absorption of perovskite single crystals can narrow down their effective optical bandgap without changing the composition. Thin methylammonium lead triiodide single crystals with tuned thickness of tens of micrometers are directly grown on hole-transport-layer covered substrates by a hydrophobic interface confined lateral crystal growth method. The spectral response of the methylammonium lead triiodide single crystal solar cells is extended to 820 nm, 20 nm broader than the corresponding polycrystalline thin-film solar cells. The open-circuit voltage and fill factor are not sacrificed, resulting in an efficiency of 17.8% for single crystal perovskite solar cells.
Stabilizing the a phase of CsPbI 3 has become one of the most critical prerequisites for its photovoltaic application. We found that mixing a small amount of sulfobetaine zwitterions in CsPbI 3 precursor solution could stabilize the a phase of CsPbI 3 films at room temperature. The interaction of zwitterion with CsPbI 3 impeded the fast crystallization of CsPbI 3 , which reduced CsPbI 3 grain size to stabilize the a phase. Solar cells with these a-phase CsPbI 3 films showed stabilized efficiency of 11.4% under 1-sun illumination.
Two-dimensional (2D) perovskites have been shown to be more stable than their three-dimensional (3D) counterparts due to the protection of the organic ligands. Herein a method is introduced to form 2D/3D stacking structures by the reaction of 3D perovskite with n-Butylamine (BA). Different from regular treatment with n-Butylammonium iodide (BAI) where 2D perovskite with various layers form, the reaction of BA with MAPbI only produce (BA)PbI, which has better protection due to more organic ligands in (BA)PbI than the mixture of 2D perovskites. Compared to BAI treatment, BA treatment results in smoother 2D perovskite layer on 3D perovskites with a better coverage. The photovoltaic devices with 2D/3D stacking structures show much improved stability in comparison to their 3D counterparts when subjected to heat stress tests. Moreover, the conversion of defective surface into 2D layers also induces passivation of the 3D perovskites resulting in an enhanced efficiency.
Twenty-micrometer-thick
single-crystal methylammonium lead triiodide
(MAPbI3) perovskite (as an absorber layer) grown on a charge-selective
contact using a solution space-limited inverse-temperature crystal
growth method yields solar cells with power conversion efficiencies
reaching 21.09% and fill factors of up to 84.3%. These devices set
a new record for perovskite single-crystal solar cells and open an
avenue for achieving high fill factors in perovskite solar cells.
Organic-inorganic halide perovskites are promising photodetector materials due to their strong absorption, large carrier mobility, and easily tunable bandgap. Up to now, perovskite photodetectors are mainly based on polycrystalline thin films, which have some undesired properties such as large defective grain boundaries hindering the further improvement of the detector performance. Here, perovskite thin-single-crystal (TSC) photodetectors are fabricated with a vertical p-i-n structure. Due to the absence of grain-boundaries, the trap densities of TSCs are 10-100 folds lower than that of polycrystalline thin films. The photodetectors based on CH NH PbBr and CH NH PbI TSCs show low noise of 1-2 fA Hz , yielding a high specific detectivity of 1.5 × 10 cm Hz W . The absence of grain boundaries reduces charge recombination and enables a linear response under strong light, superior to polycrystalline photodetectors. The CH NH PbBr photodetectors show a linear response to green light from 0.35 pW cm to 2.1 W cm , corresponding to a linear dynamic range of 256 dB.
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