When hydroxyapatite nanoparticles are included in the mesoporous scaffold for perovskite solar cells they not only improve the power conversion efficiency but sequester released Pb if broken cells are immersed in water.

Perovskite solar cells continue to attract strong attention because of their unprecedented rate of power conversion efficiency increase. CHNHPbI (MAPbI) is the most widely studied perovskite. Typically one-step (1-s) or two-step (2-s) deposition methods are used to prepare MAPbI films. Here, we investigate a new MAPbI film formation method that combines 1-s and 2-s deposition (termed 1 & 2-s) and uses systematic variation of the stoichiometric mole ratio (x) for the PbI + xMAI solutions employed. The PbI + xMAI solutions were used to deposit precursor films that were subsequently dipped in MAI solution as a second step to produce the final MAPbI films. The morphologies of the 1 & 2-s MAPbI films consisted of three crystal types: tree-like microcrystals (≫1 μm), cuboid meso-crystals (∼0.1-1 μm) and nanocrystals (∼50-80 nm). Each crystal type and their proportions were controlled by the value for x. The new 1 & 2-s deposition method produced MAPbI films with tuneable optoelectronic properties that were related to those for the conventional 1-s and 2-s films. However, the 1 & 2-s film properties were not simply a combination of those for the 1-s and 2-s films. The 1 & 2-s films showed enhanced light scattering and the photoluminescence spectra displayed a morphologically-dependent red-shift. The unique morphologies for the 1 & 2-s films also strongly influenced PbI conversion, power conversion efficiency, hysteresis and recombination. The trends for the performance parameters and hysteresis were compared for devices constructed using spiro-MeOTAD and P3HT and were similar. The 1 & 2-s method should apply to other perovskite formulations and the new insights concerning MAPbI crystal growth conditions, morphology and material properties established in this study should also be transferable.

Spin coating mixed microgel/perovskite precursor solutions gives disordered inverse opal perovskite films with morphologies and optoelectronic properties that are controlled by the microgel particles.

The mesoporous (meso)-TiO2 layer is a key component of high-efficiency perovskite solar cells (PSCs). Herein, pore size controllable meso-TiO2 layers are prepared using spin coating of commercial TiO2 nanoparticle (NP) paste with added soft polymer templates (SPT) followed by removal of the SPT at 500 °C. The SPTs consist of swollen crosslinked polymer colloids (microgels, MGs) or a commercial linear polymer (denoted as LIN). The MGs and LIN were comprised of the same polymer, which was poly­(N-isopropylacrylamide) (PNIPAm). Large (L-MG) and small (S-MG) MG SPTs were employed to study the effect of the template size. The SPT approach enabled pore size engineering in one deposition step. The SPT/TiO2 nanoparticle films had pore sizes > 100 nm, whereas the average pore size was 37 nm for the control meso-TiO2 scaffold. The largest pore sizes were obtained using L-MG. SPT engineering increased the perovskite grain size in the same order as the SPT sizes: LIN < S-MG < L-MG and these grain sizes were larger than those obtained using the control. The power conversion efficiencies (PCEs) of the SPT/TiO2 devices were ∼20% higher than that for the control meso-TiO2 device and the PCE of the champion S-MG device was 18.8%. The PCE improvement is due to the increased grain size and more effective light harvesting of the SPT devices. The increased grain size was also responsible for the improved stability of the SPT/TiO2 devices. The SPT method used here is simple, scalable, and versatile and should also apply to other PSCs.

A one-step laser process is applied to fabricate mesoporous and compact TiO2 films in 1 min for perovskite solar cells.

Ambient-air-stable methylammonium lead iodide (MAPI) perovskite thin films have been fabricated via one-step aerosol-assisted chemical vapor deposition (AACVD) from a pseudohalide Pb(SCN) 2 precursor. We compare both the bulk and surface properties of the perovskite films grown using AACVD with those made by the widely used spin-coating method. Films with larger grain sizes and much better stability in ambient air can be obtained by AACVD. By addition of excess MAI to the precursor solution, MAPI films with negligible PbI 2 impurities, as determined by X-ray diffraction, are obtained. The AACVD-grown MAPI films retain high phase purity with limited PbI 2 formation after aging in air for approximately one month. The films exhibit an optical bandgap energy of ca. 1.55 eV and the expected nominal bulk stoichiometry (within error). In addition to probing bulk properties, we utilize X-ray photoelectron spectroscopy (XPS) to scrutinize the surface characteristics in detail. We find that the use of excess MAI results in formation of neutral CH 3 NH 2 molecules at the surface. With aging time in air, the concentrations of iodine and nitrogen drop with respect to that of lead, but these changes are less severe in the AACVD-grown films compared to the counterparts made by spin-coating. Near-ambient pressure XPS is utilized to examine the surface stability of AACVD-grown films on exposure to 9 mbar H 2 O vapor. The formation of CH 3 NH 2 molecules at the surface is observed, and the MAPI phase remains largely intact. The CH 3 NH 2 molecules may passivate the surfaces and protect MAPI from degradation, providing a rationale for the observed stability of MAPI films fabricated from Pb(SCN) 2 with excess MAI.

TiO 2 has been recognized as a promising material for a wide range of emerging applications, including hydrogen generation, [1] CO 2 reduction, [2] degradation of organic pollutants, [3] self-cleaning coating, [4] quantum-dot-sensitized solar cells, [5] dyesensitized solar cells (DSSCs), [6] and more recently perovskite solar cells (PSCs). [7,8] Thermal annealing is a critical process involved in the fabrication of TiO 2 films for PSCs. For instance, a compact TiO 2 film that acts as an electron transport layer (ETL) for PSCs usually requires an annealing temperature of over 400 C to induce the crystallization from its amorphous precursor to anatase. [9,10] The fabrication of the mesoporous TiO 2 film for mesoscopic PSCs also needs high-temperature sintering of around 450-550 C to remove organic binders from TiO 2 paste and promote the interconnection between the TiO 2 nanoparticles. [11,12] A typical conventional annealing method is a time-consuming batch process involving the uses of a hotplate, furnace, or oven, for 1-3 h to fabricate these layers, including a long cooling period. [12-14] Such a process makes it challenging to develop high throughput or in-line production of PSCs. Therefore, there is a need to develop an alternative annealing method, enabling the rapid and scalable production of high-quality metal oxide films for PSCs for future commercialization. In addition, conventional annealing methods are commonly limited to below 550 C to avoid glass substrate bending or breakage due to a glass transition temperature of 564 C for substrate based on soda-lime glass. [15] Previous studies have suggested that an annealing temperature beyond 600 C enhances the crystallinity of the TiO 2 films and interconnection between the nanoparticles, which improves the performance of the PSCs and other devices. [13,16-18] To date, several alternative annealing methods have been developed to fabricate TiO 2 ETL for PSCs and DSSCs. For instance, Watson et al. demonstrated the use of an ultrafast near-IR (NIR) heating process to sinter mesoporous TiO 2 film on metal substrates for DSSCs. [19] Sánchez et al. developed a rapid flash IR method to anneal mesoporous TiO 2 film for PSCs with a peak temperature of %640 C and achieved a production rate of 15 cm 2 min À1 (1 cm 2 in 4 s). [11] Kim et al. demonstrated a flame annealing process to anneal the TiO 2 film for PSCs and DSSCs with a peak temperature up to 1000 C and

Perovskite solar cells (PSCs) are a disruptive technology that continues to attract considerable attention due to their remarkable and sustained power conversion efficiency increase. Improving PSC stability and reducing expensive hole transport material (HTM) usage are two aspects that are gaining increased attention. In a new approach, we investigate the ability of insulating polystyrene microgel particles (MGs) to increase PSC stability and replace the majority of the HTM phase. MGs are sub-micrometre crosslinked polymer particles that swell in a good solvent. The MGs were prepared using a scalable emulsion polymerisation method. Mixed HTM/MG dispersions were subsequently spin-coated onto PSCs and formed composite HTM-MG layers. The HTMs employed were poly(triaryl amine) (PTAA), poly(3-hexylthiophene) (P3HT) and Spiro-MeOTAD (Spiro). The MGs formed mechanically robust composite HTMs with PTAA and P3HT. In contrast, Spiro-MG composites contained micro-cracks due the inability of the relatively small Spiro molecules to interdigitate. The efficiencies for the PSCs containing PTAA-MG and P3HT-MG decreased by only ∼20% compared to control PSCs despite PTAA and P3HT being the minority phases. They occupied only ∼35 vol% of the composite HTMs. An unexpected finding from the study was that the MGs dispersed well within the PTAA matrix. This morphology aided strong quenching of the CHNHPbICl fluorescence. In addition, the open circuit voltages for the PSCs prepared using P3HT-MG increased by ∼170 mV compared to control PSCs. To demonstrate their versatility the MGs were also used to encapsulate P3HT-based PSCs. Solar cell stability data for the latter as well as those for PSCs containing composite HTM-MG were both far superior compared to data measured for a control PSC. Since MGs can reduce conjugated polymer use and increase stability they have good potential as dual-role PSC additives.