A Double Compatibilization Strategy To Boost the Performance of p-i-n Solar Cells Based on Perovskite Deposited in Humid Ambient Air.

Formamidinium lead iodide (FAPI) represents the most promising perovskite for single junction solar cells, exhibiting an impressive performance when deposited in a controlled nitrogen environment. In order to foster the real-world application of this technology, the deposition of FAPI in ambient air is a highly desirable prospect, as it would reduce fabrication costs. This study demonstrates that the wettability of FAPI precursors on the hole transporting layers (HTL) used to fabricate inverted p-i-n solar cells is extremely poor in ambient air, hampering the realization of a perovskite active layer with good optoelectronic quality. To address this issue, herein, a double compatibilization method is developed, which results in the attainment of remarkable performance, exceeding 21%, representing one of the highest reported efficiencies for FAPI solar cells fabricated in humid ambient air. The incorporation of a small quantity of anionic surfactant, comprising a hydrocarbon tail and a polar headgroup, sodium dodecyl sulfate (SDS), in the perovskite solution and an ultrathin layer of alumina nanoparticles on the HTL, results in a significant improvement in the wettability of the FAPI solution. This enables the reproducible deposition of highly homogeneous perovskite films with complete coverage and excellent optical and optoelectronic quality. Furthermore, devices based on FAPI with SDS exhibit enhanced stability, retaining 98% of their initial efficiency after 40 h of continuous illumination.

Resistive switching in benzylammonium-based Ruddlesden-Popper layered hybrid perovskites for non-volatile memory and neuromorphic computing.

Artificial synapses based on resistive switching have emerged as a promising avenue for brain-inspired computing. Hybrid metal halide perovskites have provided the opportunity to simplify resistive switching device architectures due to their mixed electronic-ionic conduction, yet the instabilities under operating conditions compromise their reliability. We demonstrate reliable resistive switching and synaptic behaviour in layered benzylammonium (BzA) based halide perovskites of (BzA)2PbX4 composition (X = Br, I), showing a transformation of the resistive switching from digital to analog with the change of the halide anion. While (BzA)2PbI4 devices demonstrate gradual set and reset processes with reduced power consumption, the (BzA)2PbBr4 system features a more abrupt switching behaviour. Moreover, the iodide-based system displays excellent retention and endurance, whereas bromide-based devices achieve a superior on/off ratio. The underlying mechanism is attributed to the migration of halide ions and the formation of halide vacancy conductive filaments. As a result, the corresponding devices emulate synaptic characteristics, demonstrating the potential for neuromorphic computing. Such resistive switching and synaptic behaviour highlight (BzA)2PbX4 perovskites as promising candidates for non-volatile memory and neuromorphic computing.

Formamidinium Perovskite Deposition in Ambient Air Environment for Inverted p-i-n Solar Cells.

In order to move towards large-scale fabrication, perovskite solar cells need to detach themselves from strictly controlled environmental conditions and, to this end, fabrication in ambient air is highly desirable. Formamidinium iodide perovskite (FAPI) is one of the most promising perovskites but is also unstable at room temperature, which may make the ambient air deposition more difficult. Herein, we investigated different formulations of pure FAPI for the fabrication of perovskite solar cells (PSCs) in air. We found that formulations using a mixture of N,N-Dimethylformamide (DMF): N-methyl-2-pyrrolidone (NMP) and only dimethyl sulfoxide (DMSO) are suitable for the deposition in air. To fabricate inverted p-i-n solar cells, we tested different hole transporting layers (HTLs) and observed the effects on the wettability of the perovskite solution and on the performance. A self-assembly monolayer of 2PACz (2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) was found to be the best option as a HTL, allowing us to achieve efficiencies >15% on both FTO and ITO.

Inclusion of 2D Transition Metal Dichalcogenides in Perovskite Inks and Their Influence on Solar Cell Performance.

Organic-inorganic hybrid perovskite materials have raised great interest in recent years due to their excellent optoelectronic properties, which promise stunning improvements in photovoltaic technologies. Moreover, two-dimensional layered materials such as graphene, its derivatives, and transition metal dichalcogenides have been extensively investigated for a wide range of electronic and optoelectronic applications and have recently shown a synergistic effect in combination with hybrid perovskite materials. Here, we report on the inclusion of liquid-phase exfoliated molybdenum disulfide nanosheets into different perovskite precursor solutions, exploring their influence on final device performance. We compared the effect of such additives upon the growth of diverse perovskites, namely CH3NH3PbI3 (MAPbI3) and triple-cation with mixed halides Csx (MA0.17FA0.83)(1-x)Pb (I0.83Br0.17)3 perovskite. We show how for the referential MAPbI3 materials the addition of the MoS2 additive leads to the formation of larger, highly crystalline grains, which result in a remarkable 15% relative improvement in power conversion efficiency. On the other hand, for the mixed cation-halide perovskite no improvements were observed, confirming that the nucleation process for the two materials is differently influenced by the presence of MoS2.