Organic-inorganic perovskites have emerged as an interesting class of materials that have excellent photovoltaic properties for application to solar cells. The power conversion efficiency of perovskite solar cells over 20% has already been realized through systematic optimization of materials and fabrication processes. However, the long-term stability of perovskite solar cells still need to be improved for practical applications. In this study, we introduced a multifunctional benzoquinone (BQ) additive into a precursor solution containing methylammonium iodide (MAI) and lead iodide (PbI2) used for spin-coating of perovskite films. Resulting spin-coated perovskite films containing BQ had the improved perovskite morphology and crystal quality because of intermolecular interaction between MAI and BQ slowing the rate of perovskite crystal formation. Therefore, we obtained the greatly enhanced power conversion efficiency from 10.7% to 15.6%. The reduced charge recombination loss by electron transfer from perovskite to BQ is another source of the improved efficiency. In addition to the efficiency enhancement, the BQ addition led to the extended lifetime about twenty-six times. The lifetime, at which efficiency reduces to 80% of the initial under the one-sun condition (100 mW/cm2 and AM1.5G), reached about 4000 h, one of the longest lifetimes ever reported in perovskite solar cells. The extended lifetime can be explained by the reduced formation of carrier traps originating from metallic lead during solar irradiation as the results of thermally stimulate current measurements. We believe that the present findings offer insight to help obtain efficient, stable organic-inorganic perovskite solar cells for future applications.
We have recently focused our attention on the application of perovskite materials to a semiconducting layer in field-effect transistors. Because perovskite materials are expected to promise the processability and flexibility inherent to organic semiconductors as well as the superior carrier transport inherent to inorganic semiconductors, we believe that organic semiconductor-like cost-effective, flexible transistors with inorganic semiconductor-like high carrier mobility can be realized using perovskite semiconductors in future. In this study, we have prepared the tin iodide-based perovskite as a semiconducting layer on silicon dioxide layers treated with a self-assembled monolayer containing ammonium iodide terminal groups by spin coating and, then, source-drain electrodes on the perovskite layer by vacuum deposition for the fabrication of a top-contact perovskite transistor. Because of a well-developed perovskite layer formed on the treated substrate and reduced contact resistance resulting from the top-contact structure, we have obtained a new record hole mobility of up to 12 cm2 V–1 s–1 in our perovskite transistors, which is about five times higher than a previous record hole mobility and is considered to be a very good value when compared with widely investigated organic transistors. Along with the high hole mobility, we have demonstrated that this surface treatment leads to smaller hysteresis in output and transfer characteristics and better stress stability under constant gate voltage application. These findings open the way for huge advances in solution-processable high-mobility transistors.
Organic-inorganic hybrid halide perovskites are an interesting class of materials that have excellent semiconductor properties, and demonstrated promising applications on many fields, such as solar cells, water photolysis, light emitting diodes, and amplified spontaneous emission. So far, the device lifetime is still short, and this is an important key issue faced for all researchers in this field.[1] The deep understanding of their durability and degradation mechanism is critical and necessary toward future applications.
Towards development of efficient and long-term stable perovskite solar cells (PSCs), we firstly studied the relationship between crystallization, morphology, device architecture, efficiency and durability of encapsulated PSCs. Furthermore, the degradation mechanism of the devices was elucidated by different experimental methods. The well crystallized and fully covered perovskite layer improves not only power conversion efficiency but also long-time durability. Compared to a widely used silver counter electrode, lithium fluoride/aluminum and gold electrode-based PSCs demonstrated better durability owing to less chemical degradation and interface changing. We also confirmed that the amount of accumulated charge carriers induces the degradation of the PSCs, which was proved by a thermally stimulated current technique. Finally, we realized a planar PSC with excellent durability by improving device encapsulation and optimizing device structures.
Reference:
1. M. Grätzel, Nature Materials 2014, 13, 838-842.
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