Although known since the late 19th century, organic-inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic-inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.

The thin-fi lm photovoltaic material Cu 2 ZnSnS x Se 4-x (CZTSSe) has drawn world-wide attention due to its outstanding performance and earth-abundant composition. Until recently, [ 1 ] stateof-the-art CZTSSe thin-fi lm solar cells were limited to 11.1% power conversion effi ciency (PCE), with these performance levels being achieved via a hydrazine slurry approach. [ 2 ] Other vacuum-and non-vacuum-based deposition techniques have also been successful in fabricating CZTSSe solar cells with PCE above 8%. [ 3,4 ] However, even record devices with PCE of 11% are still far below the physical limit, known as the ShockleyQueisser (SQ) limit, of about 31% effi ciency under terrestrial conditions. [ 5 ] For a solar cell with 1.13 eV bandgap such as the previous 11.1% champion, [ 2 ] the SQ limits for open circuit voltage ( V oc ) and short-circuit current density ( J sc ) are 820 mV and 43.4 mA cm −2 , respectively. The previous 11.1% champion only achieved a V oc of 460 mV and a J sc of 34.5 mA cm −2 , corresponding to about 56% and 79% of the SQ limit values. In order to boost J sc , an optical architecture with optimized transparent conductive oxide (TCO) and CdS thicknesses has recently been reported, leading to a new CZTSSe record PCE of 12.0% and a J sc that reaches 83% of the SQ limit. [ 1 ] Despite improvements in shortcircuit current, the V oc defi cit, equal to the difference between the bandgap and V oc , is currently the biggest hurdle preventing CZTSSe devices from achieving higher effi ciency. [ 6 ] Enhancement of V oc also directly improves device fi ll factor. [ 7 ] Although many factors can infl uence V oc in a solar cell, carrier generation and recombination near the charge-separating junction play a dominant role. Thus, in order to decrease the V oc defi cit and increase effi ciency beyond 12%, it is critical to understand junction characteristics, current collection, and recombination mechanisms in the current generation of devices.Here, an independently certifi ed world-record 12.6% PCE CZTSSe thin-fi lm solar cell is presented. The new champion device was fabricated using a recently described hydrazine pure-solution approach, targeting a Cu-poor and Zn-rich condition. [ 8 ] Secondary ion mass spectrometry (SIMS) shows that the obtained CZTSSe fi lms exhibit very low carbon and oxygen concentrations, comparable to fi lms fabricated by the more traditional hydrazine-slurry method. [ 9 ] The rheological properties of the particle-free solution, relative to the slurry process, signifi cantly improves the coating uniformity and fi lm structure and, consequently, the performance of the solar cells. [ 4,8 ] By simultaneously optimizing the TCO and CdS thicknesses to maximize photon transmission to the absorber and improving the bulk qualities of CZTSSe with the hydrazine pure-solution approach, both J sc and V oc are boosted in the 12.6% champion device. Device characteristics of the new champion cell, as deduced from current-voltage, quantum effi ciency, capacitance, and electron-beam-induced current (EBI...

Organic-inorganic hybrid materials promise both the superior carrier mobility of inorganic semiconductors and the processability of organic materials. A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated. Hybrids based on the perovskite structure crystallize from solution to form oriented molecular-scale composites of alternating organic and inorganic sheets. Spin-coated thin films of the semiconducting perovskite (C(6)H(5)C(2)H(4)NH(3))(2)SnI(4) form the conducting channel, with field-effect mobilities of 0.6 square centimeters per volt-second and current modulation greater than 10(4). Molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin-film transistors.

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Computational, thin-film deposition and characterization approaches have been used to examine the ternary halide semiconductor Cs 3 Sb 2 I 9 . Cs 3 Sb 2 I 9 has two known structural modifications, the 0-D dimer form (space group P6 3 /mmc, No. 194) and the 2-D layered form (P3m1, No. 164), which can be prepared via solution and solid state or gas phase reactions, respectively. Our computational investigations suggest that the layered form, which is a one-third Sb-deficient derivative of the ubiquitous perovskite structure, is a potential candidate for highband-gap photovoltaic (PV) applications. In this work, we describe details of a two-step deposition approach that enables the preparation of large grain (>1 µm) and continuous thin films of the lead-free layered perovskite derivative Cs 3 Sb 2 I 9 . Depending on the deposition conditions, films that are c-axis oriented or randomly oriented can be obtained. The fabricated thin films show enhanced stability under ambient air, compared to methylammonium lead (II) iodide perovskite films stored under similar conditions, and an optical band gap value of 2.05 eV. Photoelectron spectroscopy study yields an ionization energy of 5.6 eV, with the valence band maximum approximately 0.85 eV below the Fermi level, indicating near-intrinsic, weakly p-type character. Density Functional Theory (DFT) analysis points to a nearly direct band gap for this material (less than 0.02 eV difference between the direct and indirect band gaps) and a similar high-level of absorption compared to CH 3 NH 3 PbI 3 . The photoluminescence peak intensity of Cs 3 Sb 2 I 9 is substantially suppressed compared to that of CH 3 NH 3 PbI 3 , likely reflecting the presence of deep level defects that result in non-radiative recombination in the film, with computational results pointing to I i , I Sb , and V I as being likely candidates. A key further finding from this study is that, despite a distinctly layered structure, the electronic transport anisotropy is less pronounced due to the high ionicity of the I atoms and the strong antibonding interactions between the Sb s lone pair states and I p states, which leads to a moderately dispersive valence band.