This technoeconomic analysis shows that perovskite solar cells can emerge as a cost leader in photovoltaic power generation.

We report a reactive flux technique using the common reagent P 2 S 5 and metal precursors developed to circumvent the synthetic bottleneck for producing high-quality single-and mixed-metal two-dimensional (2D) thiophosphate materials. For the monometallic compound, M 2 P 2 S 6 (M = Ni, Fe, and Mn), phase-pure materials were quickly synthesized and annealed at 650 °C for 1 h. Crystals of dimensions of several millimeters were grown for some of the metal thiophosphates using optimized heating profiles. The homogeneity of the bimetallic thiophosphates MM′P 2 S 6 (M, M′ = Ni, Fe, and Mn) was elucidated using energy-dispersive X-ray spectroscopy and Rietveld refinement. The quality of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. We report two novel bimetallic thiophosphates, MnCoP 2 S 6 and FeCoP 2 S 6 . The Ni 2 P 2 S 6 and MnNiP 2 S 6 flux reactions were monitored in situ using variable-temperature powder X-ray diffraction to understand the formation reaction pathways. The phases were directly formed in a single step at approximately 375 °C. The work functions of the semiconducting materials were determined and ranged from 5.28 to 5.72 eV.

We have developed a laser beam induced current imaging tool for photovoltaic devices and modules that utilizes diode pumped Q-switched lasers. Power densities on the order of one sun (100 mW/cm) can be produced in a ∼40 μm spot size by operating the lasers at low diode current and high repetition rate. Using galvanostatically controlled mirrors in an overhead configuration and high speed data acquisition, large areas can be scanned in short times. As the beam is rastered, focus is maintained on a flat plane with an electronically controlled lens that is positioned in a coordinated fashion with the movements of the mirrors. The system can also be used in a scribing mode by increasing the diode current and decreasing the repetition rate. In either mode, the instrument can accommodate samples ranging in size from laboratory scale (few cm) to full modules (1 m). Customized LabVIEW programs were developed to control the components and acquire, display, and manipulate the data in imaging mode.

of these perovskites are binary 2D PbI 2 (E g = 2.3 eV) and BiI 3 (E g = 1.7 eV), which are also photoluminescent and photoconductive semiconductors whose properties have been exhaustively characterized for optoelectronic device applications. [7] PbI 2 crystallizes in the CdI 2 structure type with layers of fully edge-sharing octahedral PbI 6 units whereas BiI 3 displays an analogous structure with additional ordered vacancies to compensate for Bi being trivalent (Figure 1a,b). These materials exhibit more rigid and less dynamic lattices with negligible ion migration. We hypothesized that the combination of these two binaries to obtain a solid solution of (PbI 2 ) 1−x (BiI 3 ) x could give rise to new structural features and to the creation of Coulombic frustration in the distribution of Pb 2+ and Bi 3+ ions because of the inability of the system to produce ordered vacancies (Figure 1c,d).The very few reported investigations of (PbI 2 ) 1−x (BiI 3 ) x have involved X-ray diffraction, optical absorption properties, and nuclear quadrupole resonance spectroscopy of powder samples. [8] Here, we report that (PbI 2 ) 1−x (BiI 3 ) x compositions exhibit unprecedented conductance switching properties. Specifically, the I-V plots measured perpendicular to the layers show that as the material is biased, it "remembers" which bias direction it was under. When exposed to the opposite bias, we observe a significant reduction in the material's resistance, which we attribute to movement of stored charge. In this sense, we reveal that (PbI 2 ) 1−x (BiI 3 ) x has a type of "memory." Beginning from synthesis, we demonstrate a multi-faceted characterization approach to determining the true nature of (PbI 2 ) 1−x (BiI 3 ) x , which is critical in understanding the ion-induced charge transport and its structural properties. We find that the peculiar nanoscale separation of phases found in the 2D crystals is predominantly responsible for these properties, and we propose an ion migration mechanism as the origin of the conductance switching behavior. Material PreparationSamples of (PbI 2 ) 1−x (BiI 3 ) x were synthesized from the elemental components, Pb, Bi, and I 2 in sealed silica ampoules heated in a computer-controlled furnace and the process is detailed in Section S1.1 in the Supporting Information. All ingots of (PbI 2 ) 1−x (BiI 3 ) x were black upon removal, irrespective Layered 2D (PbI 2 ) 1−x (BiI 3 ) x materials exhibit a nonlinear dependence in structural and charge transport properties unanticipated from the combination of PbI 2 and BiI 3 . Within (PbI 2 ) 1−x (BiI 3 ) x crystals, phase integration yields deceptive structural features, while phase boundary separation leads to new conductance switching behavior observed as large peaks in current during currentvoltage (I-V) measurements (±100 V). Temperature-and time-dependent electrical measurements demonstrate that the behavior is attributed to ionic transport perpendicular to the layers. High-resolution transmission electron microscopy reveals that the structure of (PbI 2 ...