Strain Heterogeneity and Extended Defects in Halide Perovskite Devices.

Strain is an important property in halide perovskite semiconductors used for optoelectronic applications because of its ability to influence device efficiency and stability. However, descriptions of strain in these materials are generally limited to bulk averages of bare films, which miss important property-determining heterogeneities that occur on the nanoscale and at interfaces in multilayer device stacks. Here, we present three-dimensional nanoscale strain mapping using Bragg coherent diffraction imaging of individual grains in Cs0.1FA0.9Pb(I0.95Br0.05)3 and Cs0.15FA0.85SnI3 (FA = formamidinium) halide perovskite absorbers buried in full solar cell devices. We discover large local strains and striking intragrain and grain-to-grain strain heterogeneity, identifying distinct islands of tensile and compressive strain inside grains. Additionally, we directly image dislocations with surprising regularity in Cs0.15FA0.85SnI3 grains and find evidence for dislocation-induced antiphase boundary formation. Our results shine a rare light on the nanoscale strains in these materials in their technologically relevant device setting.

Novel 3D hierarchically structured cauliflower-shaped SnO2 nanospheres as effective photoelectrodes in hybrid photovoltaics.

Optical and electrical characteristics of wide bandgap metal oxides, namely the charge mobility, bandgap and energy level, directly define the performance and stability of photovoltaics. For the first time, novel three-dimensional (3D) hierarchically structured cauliflower-shaped SnO2 nanospheres with nanorods on their surface were obtained by a simple hydrothermal method without any additives at low temperature. The obtained hierarchically structured SnO2 nanospheres show large specific surface areas, proven to be efficient for sensitizer loading in both perovskite solar cells (PSCs) and dye-sensitized solar cells (DSSCs). The nanospheres could improve light harvesting and also enhance electron transport through the grain boundaries. Ultimately, a maximum power conversion efficiency of 10.37% is obtained for 3D hierarchically structured SnO2 nanosphere-based DSSCs in which SnO2 is used as the scattering layer, and a remarkable efficiency of 20.01% is achieved when 3D hierarchically structured SnO2 nanospheres are employed as the electron transport material in PSCs. We trust that our work provides a new insight into construction and structural design of highly efficient hybrid photovoltaics.

Co-axial electrospray: a versatile tool to fabricate hybrid electron transporting materials for high efficiency and stable perovskite photovoltaics.

We report a cost-effective and simple co-axial electrospray technique to fabricate a hybrid electron transporting material (ETM) consisting of a nanocomposite of hierarchically structured TiO2 nanobeads (NBs) blended with ZnO nanofibers (NFs), namely ZnO NFs + TiO2 NBs, for the first time ever. Owing to its large surface area, highly porous nature and fast electron transport, the hybrid ETM is further used in methylammonium lead iodide (CH3NH3PbI3)-based perovskite solar cells (PSCs). The optimized cells utilizing the hybrid ETM exhibit a maximum power conversion efficiency (PCEmax) of 20.27%, the highest efficiency reported thus far for hybrid ETMs. Moreover, negligible hysteresis and highly reproducible values of PCE are observed for such cells. The PCE of devices based on the ZnO NF + TiO2 NB hybrid ETM is found to be far superior to that of only ZnO NF and hierarchically structured TiO2 NB-based ETMs. Light-induced transient measurement shows that the significantly rapid electron diffusion and longer electron lifetime of the ZnO NF + TiO2 NB hybrid ETM than of only ZnO NF and hierarchically structured TiO2 NB-based ETMs contribute to the enhanced efficiency in PSCs.

Solution-processed barium hydroxide modified boron-doped ZnO bilayer electron transporting materials: Toward stable perovskite solar cells with high efficiency of over 20.5.

ZnO as an electron transporting material (ETM) in perovskite solar cells has many benefits, including low temperature processability and high mobility. We explore here for the first time, hysteresis-less mesostructured perovskite solar cells with an incredible steady-state efficiency of 20.62% particularly enhancement of the device stability. We anticipated a device structure consisting of a novel fully-solution-processed and low-temperature barium hydroxide hybridized boron-doped ZnO (B:ZnO) bilayer film as electron transport material (ETM). We modify the design of ETMs with reduced trap states density is very crucial to obtain highly stabilized power conversion efficiency (PCE) and adjustable architectures in perovskite solar cells which should produce an impact on emerging highly efficient devices and their future commercialization.

Enhanced efficiency and stability of perovskite solar cells using polymer-coated bilayer zinc oxide nanocrystals as the multifunctional electron-transporting layer.

A novel polymer-coated ZnO based bilayer electron transporting material is investigated for highly efficiency perovskite solar cells. The bilayer ETM consisting of an upper-layer of ZnO nanosheets and a lower-layer of ZnO nanoparticles demonstrates the averaged power conversion efficiency of 13.11% and a maximum power conversion efficiency of 15.13%, compared to single-layers of nanosheets (power conversion efficiency = 11.73%) and nanoparticles (power conversion efficiency = 11.08%) films. A conformal coating of a polymer such as polyethylenimine on the surface of bilayered film leading to a significant boost in power conversion efficiency upto 16.39%, thanks to the reduced work function, rapid electron transport and better perovskite infiltration into the bilayer electron transporting material.