Record-Efficiency Printable Hole-Conductor-Free Mesoscopic Perovskite Solar Cells Enabled by the Multifunctional Schiff Base Derivative.

Tailoring multifunctional additives for performing interfacial modifications, improving crystallization, and passivating defects is instrumental for the fabrication of efficient and stable perovskite solar cells (PSCs). Here, a Schiff base derivative, (chloromethylene) dimethyliminium chloride (CDCl), is introduced as an additive to modify the interface between the mesoporous TiO2 electron transport layer and the MAPbI3 light absorber during the annealing process. CDCl chemically links to TiO2 and MAPbI3 through coordination and hydrogen bonding, respectively, and results in the construction of fast electron extraction channels. CDCl also optimizes the energy-level alignment of the TiO2/MAPbI3 heterojunction and improves the pore-filling and crystallization of MAPbI3 in the mesoscopic scaffold, which inhibits nonradiative recombination and eliminates open-circuit voltage losses. As a result, an impressive power conversion efficiency of 19.74%, which is the best one ever reported, is obtained for printable carbon-based hole-conductor-free PSCs based on MAPbI3.

Printable Counter Electrode with Metal Nitride as the Conductive Medium for Perovskite Solar Cells.

Perovskite solar cells (PSCs) with a booming high power conversion efficiency (PCE) are on their road toward industrialization. A proper design of the counter electrode (CE) with low cost, high conductivity, chemical stability, and good interface contact with the other functional layer atop the perovskite layer is vital for the overall performance of PSCs. Herein, the application of titanium nitride (TiN) is reported as a conductive medium for the printable CE in hole-conductor-free mesoscopic PSCs. TiN improves the conductivity of the CE and reduces the resistivity from 20 to 10 mΩ∙cm. TiN also improves the wettability of the CE with perovskite and enhances the back interface contact, which promotes charge collection. On the other hand, TiN is chemically stable during processing and undergoes no distinguishable chemical reaction with halide perovskite. Devices with TiN as the conductive media in the CE deliver a champion PCE of 19.01%. This work supplies a considerable choice for the CE design of PSCs toward industrial applications.

Halide Perovskite Crystallization Processes and Methods in Nanocrystals, Single Crystals, and Thin Films.

Halide perovskite semiconductors with extraordinary optoelectronic properties have been fascinatedly studied. Halide perovskite nanocrystals, single crystals, and thin films have been prepared for various fields, such as light emission, light detection, and light harvesting. High-performance devices rely on high crystal quality determined by the nucleation and crystal growth process. Here, the fundamental understanding of the crystallization process driven by supersaturation of the solution is discussed and the methods for halide perovskite crystals are summarized. Supersaturation determines the proportion and the average Gibbs free energy changes for surface and volume molecular units involved in the spontaneous aggregation, which could be stable in the solution and induce homogeneous nucleation only when the solution exceeds a required minimum critical concentration (Cmin ). Crystal growth and heterogeneous nucleation are thermodynamically easier than homogeneous nucleation due to the existent surfaces. Nanocrystals are mainly prepared via the nucleation-dominated process by rapidly increasing the concentration over Cmin , single crystals are mainly prepared via the growth-dominated process by keeping the concentration between solubility and Cmin , while thin films are mainly prepared by compromising the nucleation and growth processes to ensure compactness and grain sizes. Typical strategies for preparing these three forms of halide perovskites are also reviewed.

Highly oriented MAPbI3 crystals for efficient hole-conductor-free printable mesoscopic perovskite solar cells.

Highly crystalline perovskite films with large grains and few grain boundaries are conducive for efficient and stable perovskite solar cells. Current methods for preparing perovskite films are mostly based on a fast crystallization process, with rapid nucleation and insufficient growth. In this study, MAPbI3 perovskite with inhibited nucleation and promoted growth in the TiO2/ZrO2/carbon triple mesoscopic scaffold was crystallized by modulating the precursor and the crystallization process. N-methylformamide showed high solubility for both methylammonium iodide and PbI2 and hampered the formation of large colloids in the MAPbI3 precursor solution. Furthermore, methylammonium chloride was added to reduce large colloids, which are a possible source of nucleation sites. During the crystallization of MAPbI3, the solvent was removed at a slow controlled speed, to avoid rapid nucleation and provide sufficient time for crystal growth. As a result, highly oriented MAPbI3 crystals with suppressed non-radiative recombination and promoted charge transport were obtained in the triple mesoscopic layer with disordered pores. The corresponding hole-conductor-free, printable mesoscopic perovskite solar cells exhibited a highest power conversion efficiency of 18.82%. The device also exhibited promising long-term operational stability of 1000 h under continuous illumination at maximum power point at 55 ± 5 °C and damp-heat stability of 1340 h aging at 85 °C as well as 85% relative humidity.