Zhongmin Zhou

Methylamine-Gas-Induced Defect-Healing Behavior of CH3NH3PbI3 Thin Films for Perovskite Solar Cells

We report herein the discovery of methylamine (CH3NH2) induced defect-healing (MIDH) of CH3NH3PbI3 perovskite thin films based on their ultrafast (seconds), reversible chemical reaction with CH3NH2 gas at room temperature. The key to this healing behavior is the formation and spreading of an intermediate CH3NH3PbI3⋅xCH3NH2 liquid phase during this unusual perovskite-gas interaction. We demonstrate the versatility and scalability of the MIDH process, and show dramatic enhancement in the performance of perovskite solar cells (PSCs) with MIDH. This study represents a new direction in the formation of defect-free films of hybrid perovskites.

Transformative Evolution of Organolead Triiodide Perovskite Thin Films from Strong Room-Temperature Solid-Gas Interaction between HPbI3-CH3NH2 Precursor Pair.

We demonstrate the feasibility of a nonsalt-based precursor pair--inorganic HPbI3 solid and organic CH3NH2 gas--for the deposition of uniform CH3NH3PbI3 perovskite thin films. The strong room-temperature solid-gas interaction between HPbI3 and CH3NH2 induces transformative evolution of ultrasmooth, full-coverage perovskite thin films at a rapid rate (in seconds) from nominally processed rough, partial-coverage HPbI3 thin films. The chemical origin of this behavior is elucidated via in situ experiments. Perovskite solar cells, fabricated using MAPbI3 thin films thus deposited, deliver power conversion efficiencies up to 18.2%, attesting to the high quality of the perovskite thin films deposited using this transformative process.

Doping and alloying for improved perovskite solar cells

Doping and/or alloying in the various layers in perovskite solar cells (PSCs) is playing a key role in the success of this new photovoltaic (PV) technology. Here we present a brief review of doping and alloying approaches used to enhance the efficacy of the hybrid organic–inorganic perovskite (HOIP) layer, the electron-transporting layer (ETL), the hole-transporting layer (HTL), and the electrode layers in PSCs. While the effectiveness of these approaches is beyond doubt, the fundamental understanding of doping and alloying in the majority of the cases is lacking. This presents vast research opportunities in elucidating the roles of doping and alloying, and the rational design and implementation of these approaches for enhanced PSCs performance.

CH3NH2 gas induced (110) preferred cesium-containing perovskite films with reduced PbI6 octahedron distortion and enhanced moisture stability

We report here the discovery of a fancy interaction between cesium iodide (CsI) and methylamine (CH3NH2) due to the presence of the hydrogen bond. The formed CsI·xCH3NH2 is a liquid phase, which facilitates the large scale fabrication of highly uniform cesium-containing perovskite films with strong (110) preferred orientation by the CH3NH2 gas healing process. With this method, at most 10% nonpolar Cs cations could fully dope into the crystal lattice and extremely enhance the interaction of the inorganic framework with a more symmetrical PbI6 octahedron, resulting in obvious improvement in moisture stability under continuous illumination.

Trash into Treasure: δ‐FAPbI3 Polymorph Stabilized MAPbI3 Perovskite with Power Conversion Efficiency beyond 21%

Effective passivation and stabilization of both the inside and interface of a perovskite layer are crucial for perovskite solar cells (PSCs), in terms of efficiency, reproducibility, and stability. Here, the first formamidinium lead iodide (δ-FAPbI3 ) polymorph passivated and stabilized MAPbI3 PSCs are reported. This novel MAPbI3 /δ-FAPbI3 structure is realized via treating a mixed organic cation MA x FA1-x PbI3 perovskite film with methylamine (MA) gas. In addition to the morphology healing, MA gas can also induce the formation of δ-FAPbI3 phase within the perovskite film. The in situ formed 1D δ-FAPbI3 polymorph behaves like an organic scaffold that can passivate the trap state, tunnel contact, and restrict organic-cation diffusion. As a result, the device efficiency is easily boosted to 21%. Furthermore, the stability of the MAPbI3 /δ-FAPbI3 film is also obviously improved. This δ-FAPbI3 phase passivation strategy opens up a new direction of perovskite structure modification for further improving stability without sacrificing efficiency.