High quality active layers for hybrid organic-inorganic perovskite solar cells are essential for achieving maximum device performance. However, perovskite active layers in solar cells are frequently prepared with unoptimized processes that lead to layers of inferior quality. This is often the case when research focuses on other aspects of the solar cell device, such as device design and architecture, carrier transport layers, electrodes, interlayers, etc. In this study, a single-step spin-coating method was used to prepare semi-crystalline PbI2(DMSO) complex films via evaporation-induced self-assembly. These optimized intermediate films were then used to form homogeneous methylammonium lead iodide (MAPbI3) perovskite films of optimum thickness (ca. 400 nm) with uniform surface coverage, good crystallinity, high purity, and grain sizes up to one micron, by employing a sequential deposition process involving intramolecular exchange between the PbI2(DMSO) complex film and a methylammonium iodide (MAI) layer deposited on top of it. We found that for certain ranges of MAI concentration, the formation of optimal-quality perovskite active layers was independent of MAI concentration, so long as MAI deposition occurred at specific corresponding spin speeds. Planar p-i-n perovskite solar cells comprising the optimized active layers were fabricated, and they exhibited negligible hysteresis and a maximum power conversion efficiency (PCE) of 16.72%, without any additional compositional and interfacial engineering. The latter can be used in the future to further enhance the PCE. These findings demonstrate the importance of an optimized perovskite active layer for reproducibly fabricating high-efficiency planar p-i-n photovoltaic devices. Additionally, the simplicity of the PbI2(DMSO) complex film preparation and the versatility of the MAI deposition with this fabrication method further enhances the potential of this material for large-scale processing.

The lead free double perovskite Cs2AgBiBr6 is an upcoming alternative to lead based perovskites as absorber material in perovskite solar cells. So far, the majority of investigations on this interesting material have focused on polycrystalline powders and single crystals. We present vapor and solution based approaches for the preparation of Cs2AgBiBr6 thin films. Sequential vapor deposition processes starting from different precursors are shown and their weaknesses are discussed. Single source evaporation of Cs2AgBiBr6 and sequential deposition of Cs3Bi2Br9 and AgBr result in the formation of the double perovskite phase. Additionally, we show the possibility of the preparation of planar Cs2AgBiBr6 thin films by spin coating.

Pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laser-excited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tuning of MAPbI3, enriching potentially the toolkit for engineering perovskites related photovoltaic devices.

In this article, we report low-temperature electron spin resonance (ESR) investigations carried out on solution processed three-layer inverted solar cell structures: PC61BM/CH3NH3PbI3/PEDOT:PSS/Glass, where PC61BM and PEDOT:PSS act as electron and hole transport layers, respectively. ESR measurements were conducted on ex-situ light (1 Sun) illuminated samples. We find two distinct ESR spectra. First ESR spectra resembles a typical powder pattern, associated with gx = gy = 4.2; gz = 9.2, found to be originated from Fe3+ extrinsic impurity located in the glass substrate. Second ESR spectra contains a broad (peak-to-peak line width ∼ 10 G) and intense ESR signal appearing at g = 2.008; and a weak, partly overlapped, but much narrower (peak-to-peak line width ∼ 4 G) ESR signal at g = 2.0022. Both sets of ESR spectra degrade in intensity upon light illumination. The latter two signals were found to stem from light-induced silicon dangling bonds and oxygen vacancies, respectively. Our controlled measurements confirm that these centers were generated during UV-ozone treatment of the glass substrate –a necessary step to be performed before PEDOT:PSS is spin coated. This work forms a significant step in understanding the light-induced- as well as extrinsic defects in perovskite solar cell materials.

New routes in additive devices fabrication techniques and advances in printable materials are required to meet the ever increasing demands for low-cost and large-area flexible electronics. In particular, perovskite-based materials have gained an appeal due to their unique optoelectronics and ferroelectrics properties, which may replace p-n junction in semiconductor devices. Metal-organic methylammonium lead trihalide perovskite formulations have been extensively studied in the last few years as promising materials for use in printed electronics, which do not require high temperatures or vacuum environment, contrary to conventional semiconductor fabrication techniques. In this work, digital inkjet-printing in ambient atmosphere is proposed as a deposition pathway for the fabrication of perovskite active layers in photodetector and thin-film photovoltaic device architectures. The device architecture containing a printed perovskite active layer sandwiched between TiO2 and Spiro-OMeTAD as electron and hole transport layers, respectively, as well as layer-on-layer fabrication and responsivity spectra of the perovskite-based device are presented.

Organolead iodide perovskites, CH3NH3PbI3, have attracted the attention of researchers around the world due to their optical and electrical properties. Their main characteristics include, direct band-gap (1.4 to 3.0 eV), large absorption coefficient in the visible spectrum, long carrier diffusion length and ambipolar charge transport. Aside that, perovskite thin films can be produced with low cost and are compatible with large-scale manufacture. Perovskite thin films have been synthesized mainly by spin-coating technique and thermal evaporation, which can be executed in one or two steps. Aiming to increase the light absorption, nanostructured perovskite thin films are also under intense study, since the nanostructures can absorb more light than a flat film. Thus, in this work, we reported the synthesis of perovskite (CH3NH3PbI3) nanorods by means of conversion of lead sulphide quantum dots (PbSQD). The perovskite nanorods were grown by exposing the PbSQD to a highly concentrated iodine atmosphere and then dipping the resulting film in methylammonium iodide (CH3NH3I) solution. The first step converts completely the PbSQD into lead iodide (PbI2) nanowires, ≈50 µm long and ≈200 nm diameter, through substitution of sulphur by iodine atoms and subsequent aggregation of the particles. The later step converts the PbI2 nanowires in perovskite nonorods (≈5 µm long and ≈400 nm diameter). The perovskite nanorods present a regular geometry along all its length. A preferential alignment of nanorods to the substrate plane was observed. The preliminary results show that we can control the size of nanorods through exposition time of PbSQD to iodine, which change the size of PbI2 nanowire as well. The conversion process was studied by x-ray diffraction, optical absorption, photoluminescence and scanning electron microscopy.

Thin film tin sulphide (SnS) was deposited on to molybdenum (Mo) substrates using metal organic chemical vapor deposition at 470°C using tetraethyltin and ditertiarybutylsulfide as precursors. In situ mass spectroscopy was used to study the exhaust gas species downstream of the reaction zone. The precursor vapor carrier gas was either nitrogen or hydrogen, thin film SnS only forming when the latter was used. Mass spectroscopy determined that hydrogen sulfide was being produced and playing a critical role in the vapor phase reaction process and adsorption of tin and sulfur on to the Mo surface. As-grown grain sizes were determined by scanning electron microscopy and were observed to be large averaging around 2 microns across. X-ray diffraction showed the films to be single phase SnS without any parasitic Sn2S3 or SnS2 phases, with a small amount of MoS2 also being detected.

To free ourselves from the use of fossil fuels that are highly polluting, life-threatening and not easily regenerated, new technologies are being developed to obtain alternative energy sources more efficiently. Among these technologies, there is the option to improve the performance of solid oxide fuel cells (SOFCs) to make them highly energy efficient. Solid oxide fuel cells (SOFCs) have attracted much attention because they are environmentally benign, sustainable, generate low emissions and have relative low cost. However, conventional SOFCs with yttria-stabilized zirconia (YSZ) electrolyte require high operating temperatures (800-1000°C), which often lead to material degradation problems. Given that the greatest disadvantage of SOFCs is their high operating temperature, samples of CeO2 were synthesized by spray pyrolysis method and doped with Sm2O3 and Eu2O3 to improve the ionic conductivity of the electrolyte so that it can operate at lower temperatures without losing its efficiency. The samples were analyzed using SEM, EDS, TEM. Further research will be made by small angle DRX, AFM, EIS and a prototype will be built to test the working temperature of the electrolyte.

This work reports the synthesis of undoped and alkali metal doped thermochromic vanadium dioxide thin films by sol-gel spin coating and subsequent low-temperature annealing at 450 °C in N2-H2 atmosphere. The effect of sodium and potassium on the phase transition temperature as well as on the solar modulations were investigated. A dopant concentration of 0.3 at% resulted in a reduction of the critical transition temperature (Tc) from 62 °C to 57 °C and 47 °C for the sodium and potassium doped films, respectively. Moreover, both dopants improved the solar modulations (ΔTsol) of the undoped VO2 films from 3.81 to 9.44 and 5.43 %, respectively.