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We report the synthesis method of ultralong one-dimensional (1D) inorganic perovskite nanorods with single-crystal-like molecular orientation for photodetector applications.

Dimensionality engineering is an effective approach to improve the stability and power conversion efficiency (PCE) of perovskite solar cells (PSCs). A two-dimensional (2D) perovskite assembled from bulky organic cations to cover the surface of three-dimensional (3D) perovskite can repel ambient moisture and suppress ion migration across the perovskite film. This work demonstrates how the thermal stability of the bulky organic cation of a 2D perovskite affects the crystallinity of the perovskite and the optoelectrical properties of perovskite solar cells. Structural analysis of (FAPbI3)0.95(MAPbBr3)0.05 (FA = formamidinium ion, MA = methylammonium ion) mixed with a series of bulky cations shows a clear correlation between the structure of the bulky cations and the formation of surface defects in the resultant perovskite films. An organic cation with primary ammonium structure is vulnerable to a deprotonation reaction under typical perovskite-film processing conditions. Decomposition of the bulky cations results in structural defects such as iodide vacancies and metallic lead clusters at the surface of the perovskite film; these defects lead to a nonradiative recombination loss of charge carriers and to severe ion migration during operation of the device. In contrast, a bulky organic cation with a quaternary ammonium structure exhibits superior thermal stability and results in substantially fewer structural defects at the surface of the perovskite film. As a result, the corresponding PSC exhibits the PCE of 21.6% in a reverse current-voltage scan and a stabilized PCE of 20.1% with an excellent lifetime exceeding 1000 h for the encapsulated device under continuous illumination.

Organometal halide perovskite (OHP) solar cells have been intensively studied because of their promising optoelectronic features, which has resulted in high power conversion efficiencies >23 %. Although OHP solar cells exhibit high power conversion efficiencies, their relatively poor stability is a significant obstacle to their practical use. We report that the chemical stability of OHP solar cells with respect to both moisture and heat can be improved by adding a small amount of Ag to the precursor. Ag doping increases the size of the OHP grains and reduces the size of the amorphous intergranular regions at the grain boundaries, and thereby hinders the infiltration of moisture into the OHP films and their thermal degradation. Quantum mechanical simulation reveals that Ag doping increases the energies of both the hydration reaction and heat-induced vacancy formation in OHP crystals. This procedure also improves the power conversion efficiencies of the resulting solar cells.

Two-step processes are commonly used for the fabrication of organic-inorganic perovskite solar cells; they convert a PbI2 film to a perovskite film by dipping it in CH3NH3I (MAI) solution or spin-coating the MAI solution onto it. Dipping yields perovskite films with discrete and rough morphologies, whereas spinning yields films with smooth and connected morphologies. The residual MAI solution that remains after spinning is the key factor that governs the smoothness of the resulting morphology; centrifugal force has no influence. A perovskite layer forms as soon as the MAI solution is loaded onto the PbI2 film, then the MAI residues left after spinning dissolve this outermost perovskite layer. The subsequent recrystallization of the dissolved perovskites increases the connectivity and smoothness of the crystals. The final morphology is dependent on the degrees of dissolution and recrystallization, which can be controlled by varying the processing conditions. A post-thermal treatment can be applied to induce the additional dissolution of the perovskites, which results in an increase in the final grain size while maintaining good connectivity. Combining these results, we fabricated an optimal film morphology that gives rise to perovskite solar cells with improved efficiency. The optimal perovskite film has a smooth and connected morphology as well as better carrier transport than rough and discrete films. This article provides fundamental understanding of the mechanism of formation during two-step processes of connected perovskite morphologies that can guide the further development of two-step processes for the fabrication of optimal perovskite morphologies.

The photovoltaic properties of perovskite solar cells (PSCs) are significantly influenced by the morphology of their constituent perovskite films. In this study, perovskite materials with two different morphologies, compact (c-perovskite) and nanowires (nw-perovskite), were prepared with a simple two-step spin coating solution process and their photovoltaic properties were investigated. We found that the presence of partially grown perovskite nanowires in the photoactive layer results in an excellent photovoltaic performance, i.e. a power conversion efficiency (PCE) of 18.7%. The shape and size of the perovskite nanowires are controlled by varying the concentration of N, N-dimethylformamide (DMF) in the methylammonium iodide (MAI) solution and keeping constant all other processing parameters such as the spin-coating speed and the annealing temperature. The optimal nw-perovskite film exhibits better light harvesting properties in the visible region, improved charge separation, and high charge carrier mobility. The mechanisms of charge carrier transfer in the two type of perovskites and their recombination dynamics were investigated by performing time-resolved photoluminescence (TRPL) and transient photovoltage (TPV) measurements respectively. Further, with an additional approach, the morphologies and solar cell performances of the c-perovskite and nw-perovskite films are improved by the addition of a fullerene derivative (PC60BM). These morphological advantages, together with the significant suppression of hysteresis effects, mean that the nw-perovskite:PC60BM photoactive film could be useful in the fabrication of high-performance PSCs.

Organometal halide perovskite solar cells (PeSCs) with efficiency over 25% and high stability have been reported, however, lead (Pb)-free PeSCs should be developed for the commercialization due to the toxicity of Pb. Among the candidates to replace Pb, tin (Sn) based PeSCs are leading for their low band gap and high efficiency compared to other metal candidates. In the research for Sn-based PeSCs, Sn oxidation is a critical issue to influence on both of the efficiency and stability. Here, we present a simple Cl‾-doping method to increase the resistance to oxidation in Sn-based PeSCs. Cl‾-doped perovskite film had large grains and highly-oriented crystals; these traits increased the electron and hole mobility and reduced the density of trap states in the perovskite film. Cl‾ became located at surface defects, and thereby prevented Sn oxidation. Cl‾ doping yielded PeSCs that had efficiency as high as 7.14%, with high reproducibility and stability under ambient conditions.

Organometal halide perovskites (OHPs) exhibit superior charge transport characteristics and ultralow thermal conductivities. However, thermoelectric (TE) applications of OHPs have been limited because of difficulties in controlling their carrier concentration, which is a key to optimizing their TE properties. Here, facile control of the carrier concentration in Sn-based OHPs is achieved by developing 2D crystal structures. The 2D OHP crystals are laterally oriented using a mixed solvent, and the morphology and crystal structure of the coexisting 2D/3D hybrid structures are systematically controlled via doping with methylammonium chloride. The effective number neff of inorganic octahedron layers in the 2D OHPs shows a strong positive correlation with the carrier concentration. Moreover, the 2D structure induces the quantum confinement effect, which enhances both the Seebeck coefficient and the electrical conductivity. A 2D OHP shows a high power factor of 111 µW m-1 K-2 , which is an order of magnitude greater than the power factor of its 3D counterpart.

On-demand drug delivery systems (DDSs) have been widely investigated for spatiotemporally controlled therapy with greatly improved patient compliance. However, power systems to operate the DDSs are one of the serious unmet needs constraining their further applications. Here, we report implantable organic photovoltaic cells using upconversion nanoparticles (UCNPs) for on-demand controlled drug delivery. Although skin-penetrating near infrared (NIR) light cannot be used for flexible organic photovoltaic cells, UCNPs can convert NIR light to visible light for their operation after implantation to the body. The core-shell structured UCNPs coated on flexible organic photovoltaic cells generate current flow upon NIR irradiation for triggering on-demand drug delivery from microelectromechanical system (MEMS) drug reservoirs. Gold (Au) membrane sealing the reservoirs is dissolved to AuCl4− by the applied electrical current triggering the pulsatile drug release. The successful fabrication of NIR light triggered DDS by UCNPs coated organic photovoltaic cells is confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–vis spectroscopy, photoluminescence, current density–voltage characterization, and gold thin film dissolution tests. Furthermore, on-demand model drug release tests confirm the feasibility of the new paradigm light-triggered DDS and the relevant phototherapy.