[en] Highlights: • Perovskite nanowires–based photoactive films are synthesized and investigated. • Optimal perovskite nanowire film exhibits better photovoltaic properties. • Increased PCE and suppressed hysteresis are obtained for nanowire-based devices. • The use of PC₆₀BM as an additive results in more enhanced PCE up to 18.7%. 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.

[en] Quasi-2D hybrid halide perovskites have drawn considerable attention due to their improved stability and facile tunability compared to 3D perovskites. The expansiveness of possibilities has thus far been limited by the difficulty in incorporating large ligands into thin-film devices. Here, a bulky bi-thiophene 2T ligand is focused on to develop a solvent system around creating strongly vertically-aligned (2T)${}_2$(MA)${}_6$Pb${}_7$I${}_{22}$ (n = 7) quasi-2D perovskite films. By starting with a poorly coordinating solvent (gamma-butyrolactone) and adding a small amount of dimethylsulfoxide and methanol, it is found that vertical orientation and z-uniformity is greatly improved. These are carefully examined and verified using grazing-incidence wide-angle X-ray scattering analysis and advanced optical characterizations. These films are incorporated into champion solar cells that achieve a power conversion efficiency of 13.3%, with a short-circuit current density of 18.9 mA cm${}^{-<!--\; ???\; -->2}$, an open-circuit voltage of 0.96 V, and a fill factor of 73.8%. Furthermore, the quasi-2D absorbing layers show excellent stability in moisture, remaining unchanged after hundreds of hours. In addition, 2T is compared with the more common ligands butylammonium and phenylethylammonium in this solvent system to develop heuristics and deeper understanding of how to incorporate large ligands into stable photovoltaic devices. (© 2022 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)

[en] Highlights: • Upconversion nanoparticles coated organic photovoltaic cells are developed for implantable on-demand drug delivery systems. • The skin penetrating NIR light can trigger upconversion nanoparticles to emit visible light for organic photovoltaic cells. • The gold thin films sealing the drug reservoirs can be dissolved by NIR light irradiation for on-demand drug delivery. 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.