In Operando, Photovoltaic, and Microscopic Evaluation of Recombination Centers in Halide Perovskite-Based Solar Cells

The origin of the low densities of electrically active defects in Pb halide perovskite (HaP), a crucial factor for their use in photovoltaics, light emission, and radiation detection, remains a matter of discussion, in part because of the difficulty in determining these densities. Here, we present a powerful approach to assess the defect densities, based on electric field mapping in working HaP-based solar cells. The minority carrier diffusion lengths were deduced from the electric field profile, measured by electron beam-induced current (EBIC). The EBIC method was used earlier to get the first direct evidence for the n-i-p junction structure, at the heart of efficient HaP-based PV cells, and later by us and others for further HaP studies. This manuscript includes EBIC results on illuminated cell cross sections (in operando) at several light intensities to compare optoelectronic characteristics of different cells made by different groups in several laboratories. We then apply a simple, effective single-level defect model that allows deriving the densities (N-r) of the defect acting as recombination center. We find N-r approximate to 1 x 10(13) cm(-3) for mixed A cation lead bromide-based HaP films and similar to 1 x 10(14) cm(-3) for MAPbBr(3)(Cl). As EBIC photocurrents are similar at the grain bulk and boundaries, we suggest that the defects are at the interfaces with selective contacts rather than in the HaP film. These results are relevant for photovoltaic devices as the EBIC responses distinguish clearly between high- and low-efficiency devices. The most efficient devices have n-i-p structures with a close-to-intrinsic HaP film, and the selective contacts then dictate the electric field strength throughout the HaP absorber.

Formation and Stabilization of Inorganic Halide Perovskites for Photovoltaics

Wei Guo, Ulf Anders Hagfeldt, Zaiwei Wang, Wanchun Xiang, Jiahuan Zhang

In the last decade, halide perovskites have emerged as new semiconductors that revolutionize the photovoltaic field. Among this family of materials, all-inorganic halide perovskites are becoming a research paradigm because of their outstanding photophysical properties combined with the potential of long-term stabilities against moisture and thermal stresses in practical applications. By forming high-quality inorganic halide perovskite thin films and stabilizing the three-dimensional perovskite phases, in the past few years, the state-of-the-art inorganic perovskite solar cells have achieved a power conversion efficiency of 20.37% and a promising long-term operation stability. In this review, based on the latest research progress of inorganic halide perovskites for photovoltaics, we summarized (1) the crystal structural, optical, and photophysical properties of materials; (2) the film formation methods; and (3) the stabilization strategies of inorganic perovskite phase, to provide useful guideline for fabricating devices with further enhanced performance and stability, and promoting commercial applications.

ELSEVIER2021

Co-evaporation as an optimal technique towards compact methylammonium bismuth iodide layers

Hiroyuki Kanda, Mounir Driss Mensi, Maria Cristina Momblona Rincón, Mohammad Khaja Nazeeruddin, Cristina Roldán Carmona, Albertus Adrian Sutanto

the most studied perovskite‑based solar cells reported up to date contain the toxic lead in its composition. photovoltaic research and development towards non‑toxic, lead‑free perovskite solar cells are critical to finding alternatives to reduce human health concerns associated with them. Bismuth‑based perovskite variants, especially in the form of methylammonium bismuth iodide (MBi), is a good candidate for the non-toxic light absorber. However, the reported perovskite variant MBI thin films prepared by the solution process so far suffers from poor morphology and surface coverage. In this work, we investigate for the first time the optoelectronic, crystallographic and morphological properties of MBI thin films prepared via thermal co-evaporation of MAI and BiI3. We find by modifying the precursor ratio that the layer with pure MBI composition lead to uniform, compact and homogeneous layers, broadening the options of deposition techniques for lead-free based perovskite solar cells.

2020

Formate as Anti-Oxidation Additives for Pb-Free FASnI(3) Perovskite Solar Cells

Jaeki Jeong, Jinhyun Kim, Jiyoun Seo

Pb-free Sn-based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because oftheir suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn-based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO-) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI(3)) perovskite without using A-site cationic additives. Moreover, the presence of formate results in a uniform pinhole-free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate-treated FASnI(3) has improved stability against oxidative Sn degradation. The formate-treated PSC achieves a power conversion efficiency of 12.11% at a high open-circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate.

WILEY-V C H VERLAG GMBH2022