Controlled Growth of CH3 NH3 PbI3 Using a Dynamically Dispensed Spin-Coating Method: Improving Efficiency with a Reproducible PbI2 Blocking Layer.

It is commonly believed that excess PbI2 has beneficial effects for perovskite solar cells owing to the modification of charge-transport behavior at interfaces, by surface passivation and by blocking electron-hole recombination. Here, we introduce a dynamically dispensed spin-coating technique in a two-step deposition to form a perovskite layer with controllable quantities of crystalline PbI2 . Using this technique, the concentration of CH3 NH3 I solution is kept constant at the reaction interface, ensuring smooth growth of films. By changing the spinning rate during the reaction, the PbI2 conversion ratio and perovskite cuboid size can be optimized, resulting in a power conversion efficiency improvement over control devices. This dynamically dispensed technique represents a repeatable method for compositional control in perovskite solar cells and improves our understanding of how a PbI2 blocking layer improves the performance of perovskite solar cells.

Water-Soluble Polymeric Interfacial Material for Planar Perovskite Solar Cells.

Interfacial materials play a critical role in photoelectric conversion properties as well as the anomalous hysteresis phenomenon of the perovskite solar cells (PSCs). In this article, a water-soluble polythiophene PTEBS was employed as a cathode interfacial material for PSCs. Efficient energy level aligning and improved film morphology were obtained due to an ultrathin coating of PTEBS. Better ohmic contact between the perovskite layer and the cathode also benefits the charge transport and extraction of the device. Moreover, less charge accumulation at the interface weakens the polarization of the perovskite resulting in a relatively quick response of the modified device. The ITO/PTEBS/CH3NH3PbI3/spiro-MeOTAD/Au cells by an all low-temperature process achieved power conversion efficiencies of up to 15.4% without apparent hysteresis effect. Consequently, the utilization of this water-soluble polythiophene is a practical approach for the fabrication of highly efficient, large-area, and low-cost PSCs and compatible with low-temperature solution process, roll-to-roll manufacture, and flexible application.

Morphology control of the perovskite films for efficient solar cells.

In the past two years, the power conversion efficiency (PCE) of organic-inorganic hybrid perovskite solar cells has significantly increased up to 20.1%. These state-of-the-art new devices surpass other third-generation solar cells to become the most promising rival to the silicon-based solar cells. Since the morphology of the perovskite film is one of the most crucial factors to affect the performance of the device, many approaches have been developed for its improvement. This review provides a systematical summary of the methods for morphology control. Introductions and discussions on the mechanisms and relevant hotspots are also given. Understanding the growth process of perovskite crystallites has great benefits for further efficiency improvement and enlightens us to exploit new technologies for large-scale, low-cost and high-performance perovskite solar cells.

Improved hole-transporting property via HAT-CN for perovskite solar cells without lithium salts.

A nonadditive hole-transporting material (HTM) of a triphenylamine derivative of N,N'-di(3-methylphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl (TPD) is used for the organic-inorganic hybrid perovskite solar cells. The power conversion efficiency (PCE) can be significantly enhanced by inserting a thin layer of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) without adding an ion additive because the hole-transporting properties improve. The short-circuit current density (J(sc)) increases from 8.5 to 13.1 mA/cm(2), the open-circuit voltage (V(oc)) increases from 0.84 to 0.92 V, and the fill-factor (FF) increases from 0.45 to 0.59, which corresponds to the increase in PCE from 3.2% to 7.1%. Moreover, the PCE decreases by only 10% after approximately 1000 h without encapsulation, which suggests an alternative method to improve the stability of perovskite solar cells.

A hydrophobic hole transporting oligothiophene for planar perovskite solar cells with improved stability.

An oligothiophene derivative named DR3TBDTT with high hydrophobicity was synthesized and functioned as the hole transporting material without an ion additive. 8.8% of power conversion efficiency was obtained for CH3NH3PbI3-xClx based planar solar cells with improved stability, compared to devices using Li-TFSI doped spiro-MeOTAD.

Improved light absorption and charge transport for perovskite solar cells with rough interfaces by sequential deposition.

Recently, highly efficient solar cells based on organic-inorganic perovskites have been intensively reported for developing fabricating methods and device structures. Additional power conversion efficiency should be gained without increasing the thickness and the complexity of the devices to accord with practical applications. In this paper, a rough interface between perovskite and HTM was fabricated in perovskite solar cells to enhance the light scattering effect and improve the charge transport. The parameters related to the morphology have been systematically investigated by sequential deposition. Simultaneous enhancements of short-circuit current and power conversion efficiency were observed in both CH3NH3PbI3 and CH3NH3PbI3-xClx devices containing the rough interface, with power conversion efficiencies of 10.2% and 10.8%, respectively. Our finding provides an efficient and universal way to control the morphology and further optimize perovskite solar cells for devices by sequential deposition with various structures.

A highly efficient mesoscopic solar cell based on CH3NH3PbI(3-x)Cl(x) fabricated via sequential solution deposition.

A mixed halide perovskite of CH3NH3PbI(3-x)Cl(x) is synthesized via two-step sequential solution deposition by using a mixture of PbCl2 and PbI2 as the precursor to overcome the low solubility of pure PbCl2 with easy morphology control. 11.7% power conversion efficiency is achieved for the mesoscopic cell, much higher than the cell constructed via a spin-coating process.