Prof Henry Snaith FRS

Abstract:

Metal halide perovskites have been demonstrated as one of the most promising materials for low-cost and high-performance photovoltaic applications. However, due to the susceptible crystallization process of perovskite films on planar substrates and the high sensitivity of the physical and optoelectronic nature of the internal interfaces within the devices, researchers in different laboratories still experience poor reproducibility in fabricating efficient perovskite solar cells with planar heterojunction device structures. In this methods paper, we present detailed information on the reagents, equipment, and procedures for the fabrication of planar perovskite solar cells in both “regular” n-i-p and “inverted” p-i-n architectures based on one-step solution-processed methylammonium lead triiodide (MAPbI3) perovskite films. We discuss key parameters affecting the crystallization of perovskite and the device interfaces. This methods paper will provide a guideline for the reproducible fabrication of planar heterojunction solar cells based on MAPbI3perovskite films. We believe that the shared experience on MA-based perovskite films and planar solar cells will be also useful for the optimization process of perovskites with varied compositions and other emerging perovskite-based optoelectronic devices.

Abstract:

In this work, solar cells with a freshly made CH3 NH3 PbI3 perovskite film showed a power conversion efficiency (PCE) of 15.4 % whereas the one with 50 days aged perovskite film only 6.1 %. However, when the aged perovskite was covered with a layer of Al2 O3 deposited by atomic layer deposition (ALD) at room temperature (RT), the PCE value was clearly enhanced. X-ray photoelectron spectroscopy study showed that the ALD precursors are chemically active only at the perovskite surface and passivate it. Moreover, the RT-ALD-Al2 O3 -covered perovskite films showed enhanced ambient air stability.

Abstract:

We present herein an experimental screening study that assesses how partially replacing Pb in methylammonium lead triiodide perovskite films with nine different alternative, divalent metal species, B = {Co, Cu, Fe, Mg, Mn, Ni, Sn, Sr, and Zn}, influences photovoltaic performance and optical properties. Our findings indicate the perovskite film is tolerant to most of the considered homovalent metal species with lead-cobalt compositions yielding the highest power conversion efficiencies when less than 6% of the Pb2+ ions are replaced. Through subsequent materials characterisation, we demonstrate for the first time that partially substituting Pb2+ at the B-sites of the perovskite lattice is not restricted to Group IV elements but is also possible with at least Co2+. Moreover, adjusting the molar ratio of Pb:Co in the mixed-metal perovskite affords new opportunities to tailor the material properties while maintaining stabilised device efficiencies above 16% in optimised solar cells. Specifically, crystallographic analysis reveals that Co2+ incorporates into the perovskite lattice and increasing its concentration can mediate a crystal structure transition from the cubic to tetragonal phase at room-temperature. Likewise, Co2+ substitution continually modifies the perovskite work function and band edge energies without either changing the band gap or electronically doping the intrinsic material. By leveraging this orthogonal dimension of electronic tunability, we achieve remarkably high open-circuit voltages up to 1.08 V with an inverted device architecture by shifting the perovskite into a more favourable energetic alignment with the PEDOT:PSS hole transport material.

Abstract:

A robust and expedient gas quenching method is developed for the solution deposition of hybrid perovskite thin films. The method offers a reliable standard practice for the fabrication of a non-exhaustive variety of perovskites exhibiting excellent film morphology and commensurate high performance in both regular and inverted structured solar cell architectures.

Abstract:

Nanomaterials with different morphologies were placed in discrete layers through the thickness of a negative electrode for a Li ion battery to exploit effectively the intrinsic energy storage capabilities of each nanomaterial morphology and to improve the overall dynamics of Li ion diffusion. The two layer electrode showed a combination of high volumetric capacity and rate capability that surpassed the performance of conventional randomly blended electrodes comprising the same nanomaterials. Local Li ion concentrations were measured through the electrode thickness and clearly showed the benefits of the layered structure over the alternatives. The two layer electrode was fabricated by a flexible and scalable suspension atomization and spray deposition technique with generic potential for improved layered electrodes in a wide range of applications.