Hydroxyapatite nanoparticles (HAP NPs) are blended with TiO₂ NPs to prepare mixed mesoporous scaffolds which are used to prepare high efficiency perovskite solar cells (PSCs) with a best power conversion efficiency (PCE) of 20.98%. HAP not only increases the PCE but also limits the concentration of Pb released in water from intentionally broken PSCs by ion sequestration thereby potentially offering a promising in-device fail-safe system.

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 CH₃NH₃PbI_3−xCl_x 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.

Semitransparent perovskite solar cells (PSCs) have excellent potential for solar window applications. A major challenge exists, however, in achieving uniform coverage for thin perovskite films. Unfortunately, uncontrolled pinhole formation is a common problem for such films that obstructs development, especially for large area devices. In this study, we used very small (submicrometer) swellable polymer colloid particles (microgels) as additives to prepare uniform thin CH₃NH₃PbI₃ (MAPI) perovskite films. Microgels (MGs) are good film-formers and promoted formation of semitransparent (ST) perovskite films with improved coverage. The MGs act as colloidal sponges and delayed release of perovskite precursors, thereby delaying perovskite crystallization. The ST films prepared using MGs had fewer pinholes compared to the MG-free control films. X-ray photoelectron spectroscopy showed evidence of Pb coordination by the MGs and they were shown to passivate MAPI. Remarkably, the submicrometer MGs used in this study decreased light scattering for the ST films. Planar devices constructed using a 10 nm ST film with an average visible transmittance of 46.8% gave an average power conversion efficiency (PCE) of 7.69%, which compares favorably to literature values. The average PCE increased to 9.62% upon inclusion of a thin meso-TiO₂ layer. These PCE values are significantly higher than that achieved for the MG-free ST control (4.93%). The MGs and approaches used here are scalable and should apply to other ST perovskite films, solar cells, and, potentially, tandem devices.