Impact of PbI₂ Passivation and Grain Size Engineering in CH₃NH₃PbI₃ Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique

Abstract

With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley-Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering-e.g., addition of MASCN (MA=methylammonium) and excess PbI 2 have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, we use a newly developed carrier-resolved photo-Hall (CRPH) characterization technique that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n-type MAPbI 3 films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI 2 added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120-2100 nm) and MASCN addition induce no significant change in carrier-related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI 2 must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI 3 optoelectronic properties as elucidated by the new CRPH approach.

p-Type molecular doping by charge transfer in halide perovskite

“…As electrical doping may influence semiconductor optoelectronic properties, we performed carrier-resolved photo-Hall (CRPH) 40,41 measurements on undoped and 1% doped MAPb 0.5 Sn 0.5 I 3 to assess the impact of F4TCNQ addition on carrier mobility, lifetime and diffusion length. The CRPH analysis relies on the evolution of the Hall coefficient H with conductivity s obtained at different light intensities.…”

Perovskite Passivation Strategies for Efficient and Stable Solar Cells

“…Reproduced with permission. [ 81 ] Copyright 2019, Wiley‐VCH. k) Schematic diagram of ligand‐modulation technology and morphology of different perovskite films processed by CTAB, CTAC, OTAB, DTAB.…”

“…[79,80] Euvrard et al developed a new carrier-resolved photo-Hall (CRPH) characterization technique, which was used to reveal majority and minority carrier properties within the same sample and over a wide range of illumination conditions. [81] Figure 4j shows the evolution of the Hall coefficient H to the layer conductivity σ for one set of samples processed with and without extra PbI 2 . The slope dln(H)/dln(σ) extracted from the H-σ plot is used to extract the Δμ value which is necessary to resolve the photo-Hall equations.…”

Diethylammonium Iodide Assisted Grain Growth with Sub‐Grain Cluster to Passivate Grain Boundary for CH3NH3PbI3 Perovskite Solar Cells

“…[ 19 ] Similarly, the addition of methylammonium thiocyanate and excess PbI 2 can modify perovskite film's grain to passivate the bulk‐defects. [ 20 ] Yang and co‐workers have used imidazole sulfonate zwitterion as a bifunctional additive in the methylammonium lead triiodide (MAPbI 3 ) to obtain the ordered crystalline film with passivated GBs. [ 21 ] The photoactive layer (PAL) with 2D perovskite on 3D perovskite's surface has been recognized to be very effective to improve the stability of the PSCs, but some trials must be made to trade‐off moisture endurance against photovoltaic efficiency because of the great tolerance to moist environment and the insulation characteristic to carrier‐migration of 2D materials’ hydrophobic groups.…”