Perovskite Solar Cells on Corrugated Substrates with Enhanced Efficiency

Design of optimized photonic-structure and analysis of adding a SiO2 layer on the parallel CH3NH3PbI3/CH3NH3SnI3 perovskite solar cells

So far, remarkable achievements have been obtained by optimizing the device architecture and modeling of solar cells is a precious and very effective way to comprehend a better description of the physical mechanisms in solar cells. As a result, this study has inspected two-dimensional simulation of perovskite solar cells (PSCs) to achieve a precise model. The solution which has been employed is based on the finite element method (FEM). First, the periodically light trapping (LT) structure has been replaced with a planar structure. Due to that, the power conversion efficiency (PCE) of PSC was obtained at 14.85%. Then, the effect of adding an SiO2 layer to the LT structure as an anti-reflector layer was investigated. Moreover, increasing the PCE of these types of solar cells, a new structure including a layer of CH3NH3SnI3 as an absorber layer was added to the structure of PSCs in this study, which resulted in 25.63 mA/cm2 short circuit current (Jsc), 0.96 V open circuit voltage (Voc), and 20.48% PCE.

Interior/Interface Modification of Textured Perovskite for Enhanced Photovoltaic Outputs of Planar Solar Cells by an In Situ Growth Passivation Technology

To compensate for the photoelectric losses of planar heterojunction perovskite solar cells (PSCs), the development of high-quality textured absorbers with excellent light-harvesting ability and carrier extraction/transfer efficiency is of great significance to achieve a high-efficiency stable photovoltaic output. In this paper, we propose an in situ growth passivation technique to construct high-performance textured absorbers by adding a 2-amino-4-chlorophenol (AC) modifier consisting of multiple groups during the growth of textured perovskite. Initially, according to the Ostwald ripening mechanism, the strongly polar dimethylformamide (DMF) was used as the etchant to systematically study its synergistic effect on the morphology evolution, crystallization kinetics, light-trapping capability, and photovoltaic loss of textured absorbers. An appropriate amount of DMF induces formamidinium cations (FA⁺) to replace methylammonium cations (MA⁺) in the perovskite lattice while etching the absorber to form a texture configuration, which effectively broadens the spectral absorption range, thus greatly improving the light-trapping capacity and short-circuit current density of planar PSCs. In contrast, excess DMF deteriorates the device performance due to the excessive corrosion of the perovskite. Moreover, the introduction of the AC modifier is of great significance for passivating deep-level defects and accelerating the charge extraction/transfer. Owing to the electron-donating nature of the Lewis base, the hydroxyl groups with a higher electron density in AC molecules can better coordinate with Pb²⁺ ion defects, which effectively improves the crystallinity of the textured perovskite, thus suppressing the nonradiative recombination and ultimately improving the photovoltaic outputs of modified devices, particularly the fill factor and the open-circuit voltage. Thus, the photovoltaic performance of the AC-modified planar PSC is significantly better than that of the conventional textured device, with a reverse efficiency of 21.18% and forward efficiency of 20.77%. Owing to the synergistic effect of (1) the superior optical properties of the textured perovskite induced by DMF and (2) excellent charge dynamics driven by AC, the functionalized devices without encapsulation also exhibited good photovoltaic output stability and reproducibility. This work provides novel insights into the growth mechanism of textured absorbers and paves the way for more efficient and stable planar PSCs.

Nanostructured front electrodes for perovskite/c-Si tandem photovoltaics

The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm² absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.

Growth of Compact CH3NH3PbI3 Thin Films Governed by the Crystallization in PbI2 Matrix for Efficient Planar Perovskite Solar Cells

As a convenient preparation technique, a two-step method, which is normally done by spin-coating CH₃NH₃I onto PbI₂ film followed by a thermal annealing, is generally used to prepare solution-processed CH₃NH₃PbI₃ films for planar perovskite solar cells. Here, we prepare the compact CH₃NH₃PbI₃ thin films by the two-step method at a low temperature (<80 °C) and investigate the effects of PbI₂ crystallization on the structure-property correlation in the CH₃NH₃PbI₃ films. It is found that the importance of the crystallization in PbI₂ matrix lies in governing the transition from the (001) plane of trigonal PbI₂ to the (002) plane of tetragonal CH₃NH₃PbI₃ in the rapid reaction process for atoms to coordinate into perovskite during spin-coating, which actually determines the morphology and the type of vacancy defects in resulting perovskite; a better crystallized PbI₂ film has a much stronger ability to react with CH₃NH₃I solution and produces larger CH₃NH₃PbI₃ grains with a higher crystallinity. The CH₃NH₃PbI₃/TiO₂ planar solar cell derived from a better crystallized PbI₂ film exhibits significantly improved performance and stability as the result of the higher crystallinity inside the perovskite film. Moreover, it is demonstrated that the crystalline PbI₂ film matrix subjected to the annealing after a slow heating process prior to contacting CH₃NH₃I solution is more effective for CH₃NH₃PbI₃ formation than that with a direct annealing history. The results in this paper provide a guide for preparing high-quality CH₃NH₃PbI₃ thin films for efficient perovskite solar cells and CH₃NH₃PbI₃ interfacial films over the layers susceptible to temperature.

Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with high luminescence and stability

Zero-dimensional (0D) perovskite Cs₄PbBr₆ has been speculated to be an efficient solid-state emitter, exhibiting strong luminescense on achieving quantum confinement. Although several groups have reported strong green luminescence from Cs₄PbBr₆ powders and nanocrystals, doubts that the origin of luminescence comes from Cs₄PbBr₆ itself or CsPbBr₃ impurities have been a point of controversy in recent investigations. Herein, we developed a facile one-step solution self-assembly method to synthesize pure zero-dimensional rhombohedral Cs₄PbBr₆ micro-disks (MDs) with a high PLQY of 52% ± 5% and photoluminescence full-width at half maximum (FWHM) of 16.8 nm. The obtained rhombohedral MDs were high quality single-crystalline as demonstrated by XRD and SAED patterns. We demonstrated that Cs₄PbBr₆ MDs and CsPbBr₃ MDs were phase-separated from each other and the strong green emission comes from Cs₄PbBr₆. Power and temperature dependence spectra evidenced that the observed strong green luminescence of pure Cs₄PbBr₆ MDs originated from direct exciton recombination in the isolated octahedra with a large binding energy of 303.9 meV. Significantly, isolated PbBr₆^4- octahedra separated by a Cs⁺ ion insert in the crystal lattice is beneficial to maintaining the structural stability, depicting superior thermal and anion exchange stability. Our study provides an efficient approach to obtain high quality single-crystalline Cs₄PbBr₆ MDs with highly efficient luminescence and stability for further optoelectronic applications.

Facile Face-Down Annealing Triggered Remarkable Texture Development in CH3NH3PbI3 Films for High-Performance Perovskite Solar Cells

Herein, we demonstrate that the facile face-down annealing route which effectively confines the evaporation of residual solvent molecules in one-step deposited precursor films can controllably enable the formation of (110) textured CH₃NH₃PbI₃ films consisting of high-crystallinity well-ordered micrometer-sized grains that span vertically the entire film thickness. Such microstructural features dramatically decrease nonradiative recombination sites as well as greatly improve the transport property of charge carries in the films compared with that of the nontextured ones obtained by the conventional annealing route. As a consequence, the planar-heterojunction perovskite solar cells with these textured CH₃NH₃PbI₃ films exhibit significantly enhanced power conversion efficiency (PCE) along with small hysteresis and excellent stability. The champion cell yields impressive PCE boosting to 18.64% and a stabilized value of around 17.22%. Particularly, it can maintain 86% of its initial value after storage for 20 days in ambient conditions with relative humidity of 10-20%. Our work suggests a facile and effective route for further boosting the efficiency and stability of low-cost perovskite solar cells.