Snaith group

Abstract:

While (111)-dominated perovskite films hold the potential for high-stability solar cells, most studies have primarily focused on modulating the (111) facets, overlooking the distribution and formation mechanism of the nondominant (100) facets. In this study, we delve into the (111) orientation via solvent regulation and investigate the evolution of facet distribution using various diffraction techniques. The findings reveal that simply stacking (111) facets does not inherently enhance solar cells. Instead, the distribution of nondominant (100) facets in (111)-dominated films significantly influences both photoelectric property and stability. These observations highlight the critical need to manage the interplay between dominant and nondominant facets. The study further offers strategies for addressing facet heterogeneity to achieve a uniform facet distribution. This research provides a comprehensive framework for understanding (111)-dominated perovskites and offers valuable guidance for designing high-performance perovskite solar cells.

Abstract:

Reducing heterointerface nonradiative recombination is a key challenge for realizing highly efficient perovskite solar cells (PSCs). Motivated by this, a facile strategy is developed via interfacial energetics reversal to functionalize perovskite heterointerface. A surfactant molecule, trichloro[3-(pentafluorophenyl)propyl]silane (TPFS) reverses perovskite surface energetics from intrinsic n-type to p-type, evidently demonstrated by ultraviolet and inverse photoelectron spectroscopies. The reconstructed perovskite surface energetics match well with the upper deposited hole transport layer, realizing an exquisite energy level alignment for accelerating hole extraction across the heterointerface. Meanwhile, TPFS further diminishes surface defect density. As a result, this cooperative strategy leads to greatly minimized nonradiative recombination. PSCs achieve an impressive power conversion efficiency of 25.9% with excellent reproducibility, and a nonradiative recombination-induced qV_oc loss of only 57 meV, which is the smallest reported to date in n-i-p structured PSCs.

Abstract:

Abstract:

Metal-halide perovskite solar cells have achieved power conversion efficiencies comparable to those of silicon photovoltaic (PV) devices, approaching 27% for single-junction devices. The durability of the devices, however, lags far behind their performance. Their practical implementation implies the subjection of the material and devices to temperature cycles of varying intensity, driven by diurnal cycles or geographical characteristics. Thus, it is vital to develop devices that are resilient to temperature cycling. This Perspective analyses the behaviour of perovskite devices under temperature cycling. We discuss the crystallographic structural evolution of the perovskite layer, reactions and/or interactions among stacked layers, PV properties and photocatalysed thermal reactions. We highlight effective strategies for improving stability under temperature cycling, such as enhancing material crystallinity or relieving interlayer thermal stress using buffer layers. Additionally, we outline existing standards and protocols for temperature cycling testing and we propose a unified approach that could facilitate valuable cross-study comparisons among scientific and industrial research laboratories. Finally, we share our outlook on strategies to develop perovskite PV devices with exceptional real-world operating stability.

Abstract:

<jats:title>Abstract</jats:title><jats:p>2D lead halide perovskites (2DPs) offer chemical compatibility with 3D perovskites and enhanced stability, which are attractive for applications in photovoltaic and light‐emitting devices. However, such lowered structural dimensionality causes increased excitonic effects and highly anisotropic charge‐carrier transport. Determining the diffusivity of excitations, in particular for out‐of‐plane or inter‐layer transport, is therefore crucial, yet challenging to achieve. Here, an effective method is demonstrated for monitoring inter‐layer diffusion of photoexcitations in (PEA)<jats:sub>2</jats:sub>PbI<jats:sub>4</jats:sub> thin films by tracking time‐dependent changes in photoluminescence spectra induced by photon reabsorption effects. Selective photoexcitation from either substrate‐ or air‐side of the films reveals differences in diffusion dynamics encountered through the film profile. Time‐dependent diffusion coefficients are extracted from spectral dynamics through a 1D diffusion model coupled with an interference correction for refractive index variations arising from the strong excitonic resonance of 2DPs. Such analysis, together with structural probes, shows that minute misalignment of 2DPs planes occurs at distances far from the substrate, where efficient in‐plane transport consequently overshadows the less efficient out‐of‐plane transport in the direction perpendicular to the substrate. Through detailed analysis, a low out‐of‐plane excitation diffusion coefficient of (0.26 ± 0.03) ×10<jats:sup>−4</jats:sup> cm<jats:sup>2</jats:sup> s<jats:sup>−1</jats:sup> is determined, consistent with a diffusion anisotropy of ≈4 orders of magnitude.</jats:p>