spin-coating, [2,3] two-step interdiffusion, [4] dip-coating, [4] inkjet printing, [5,6] and spray pyrolysis. [7] These solution-based fabrication methods of perovskite films have been used in a variety of devices ranging from field-effect transistors, [8] light-emitting devices (LED), [9] photodetectors, [10,11] to solar cells. [2][3][4]12] Although most perovskite thin films are fabricated using a saltbased precursor solution, little effort has been dedicated to characterizing the structure and time-dependent evolution of the species present in solution and the impact this has on the quality of the resulting films. Furthermore, it has been shown that additives to the precursor solution can impact the nucleation rate, morphology, grain size, and crystallinity of the perovskite. Additives, such as polymers, [13] small molecules, [14,15] metal ions, [16] water, [17] or acids, [18][19][20][21][22][23][24] can play a vital role in material quality, enabling improvements in material stability, optoelectronic properties, and photovoltaic performance.Work by Yan et al. characterized the 1:1 CH 3 NH 3 I:PbI 2 stoichiometric precursor solution as a colloidal dispersion in a mother solution, rather than a pure solution. [25] When fabricated on planar substrate, this colloidal solution forms films with poor morphology, due to the presence of rodshaped colloids comprised of a soft coordination complex in the form of a lead polyhalide framework. [25] The authors show that the colloid distribution can be tuned by varying the organic to inorganic compound ratio in the precursor solution, using excess CH 3 NH 3 I (MAI) and CH 3 NH 3 Cl (MACl). However, the authors were unable to remove the 1D PbI 2 rod-like structures in the widely used stoichiometric 1:1 precursor solution. Adding excess organic cation to dissolve these colloids may be incompatible with recently published mixed-cation perov skites that contain both organic and inorganic cations, [26][27][28][29] since this will alter the precise [HC(NH 2 ) 2 ] + (formamidinium, FA) to Cs ratio, which is required to form the appropriate perovskite composition. In addition, FAI has a lower effective volatility than MACl, for instance, and hence excess quantities will not be so readily removed. Herein, we address this problem by utilizing acidic additives to trigger the dissolution of the Perovskite Solar CellsIn recent years, metal halide perovskite solar cells have gained tremendous attention, reaching certified efficiencies of 22.1% power conversion efficiency. [1] This rapid success is partly due to a versatile solution-based fabrication process which allows for a wide range of deposition techniques such as:

In analogy to their oxide counterparts, two-dimensional (2D) hybrid organic–inorganic perovskites have been classified, in many cases, as either Dion–Jacobson (DJ) or Ruddlesden–Popper (RP) structures. We quantified the offset of the inorganic layers to allow the structures of hybrid organic inorganic perovskite to be consistently related to these two structure types. We report the structures of a family of 2D hybrid structures, (4-Y-C6H4CH2NH3)2PbI4 (where Y = F, Cl, Br, I), which consist of single ⟨100⟩-terminated perovskite sheets separated by p-halobenzylammonium cations. In contrast to the previous RP structure of (C6H5CH2NH3)2PbI4, where the inorganic layers are offset from each other, the Y = F, Cl, and Br examples tend toward the DJ structure, in which successive layers eclipse each other, despite the use of an organic monocation. Close Y···I approaches suggest that halogen bonding plays a role in these structures. Use of Y = I, for which stronger halogen bonding is expected and is also suggested by a more linear C–Y···I angle, results in an RP-like structure. The stability of the (4-Y-C6H4CH2NH3)2PbI4 derivatives under ambient conditions is substantially higher for Y = Br and I than for Y = H, F, and Cl.

We demonstrate a method for controlled p-doping of the halide perovskite surface using molecular dopants, resulting in reduced non-radiative recombination losses and improved device performance.

No abstract

The dimers of pentamethyliridocene and ruthenium pentamethylcyclopentadienyl mesitylene, (IrCp*Cp)2 and (RuCp*mes)2, respectively, are shown here to be effective solution-processable reagents for lowering the work functions of electrode materials; this approach is compared to the use of solution-deposited films of ethoxylated poly(ethylenimine) (PEIE). The work functions of indium tin oxide (ITO), zinc oxide, and gold electrodes can be reduced to 3.3-3.4 eV by immersion in a toluene solution of (IrCp*Cp)2; these values are similar to those that can be obtained by spin-coating a thin layer of PEIE onto the electrodes. The work-function reductions achieved using (IrCp*Cp)2 are primarily attributable to the interface dipoles associated with the formation of submonolayers of IrCp*Cp(+) cations on negatively charged substrates, which in turn result from redox reactions between the dimer and the electrode. The electrical properties of C60 diodes with dimer-modified ITO cathodes are similar to those of analogous devices with PEIE-modified ITO cathodes.