Effect of chloride substitution on interfacial charge transfer processes in MAPbI perovskite thin film solar cells: planar mesoporous.

For photovoltaic devices based on hybrid organic-inorganic perovskite thin films, the cell architecture is a vital parameter in defining the macroscopic performance. However, the understanding of the correlation between architecture and carrier dynamics in perovskite thin films has remained elusive. In this work, we utilize concerted materials characterization and optical measurements to investigate the role of chloride addition in PSC devices with two different architectures.

Optoelectronic Dichotomy of Mixed Halide CHNHPb(BrCl ) Single Crystals: Surface versus Bulk Photoluminescence.

In this work, the spatially dependent recombination kinetics of mixed-halide hybrid perovskite CHNHPb(BrCl ) (0 ≤ x ≤ 0.19) single crystals are investigated using time-resolved photoluminescence spectroscopy with one- and two-photon femtosecond laser excitation. The introduction of chloride by substituting a fraction of the bromide leads to a decreased lattice constant compared to pure bromide perovskite ( x = 0) and a higher concentration of surface defects.

Complete Conversion of PbI to Methyl Ammonium PbI Improves Perovskite Solar Cell Efficiency.

One major disadvantage to the two-step deposition method of perovskite films is the incomplete conversion from PbI to perovskite resulting in the presence of a thick PbI layer, which hinders charge carrier transportation. In this study, a quaternary ammonium salt has been used to manipulate the crystallization of PbI in the first deposition step, which leads to facile incorporation of the methylammonium iodide into the Pb-I lattice and promotes the conversion of PbI to perovskite leading to improved device performance.

Femtosecond time-resolved transient absorption spectroscopy of CH3NH3PbI3 perovskite films: evidence for passivation effect of PbI2.

CH3NH3PbI3 perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450-800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ∼750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ∼750 nm from laser-induced fluorescence that occurs red-shifted at ∼780 nm.

Combination of optical and electrical loss analyses for a Si-phthalocyanine dye-sensitized solar cell.

In order to promote the development of solar cells with varying types of sensitizers including dyes and quantum dots, it is crucial to establish a general experimental analysis that accounts for all important optical and electrical losses resulting from interfacial phenomena. All of these varying types of solar cells share common features where a mesoporous scaffold is used as a sensitizer loading support as well as an electron transport material, which may result in light scattering. The loss of efficiency at interfaces of the sensitizer, the mesoporous TiO2 nanoparticle films, the FTO conductive layer, and the supportive glass substrate should be considered in addition to the photoinduced electron transport properties within a cell.

Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing.

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a reversible fashion.