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 PbI2have 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, a newly developed carrier‐resolved photo‐Hall (CRPH) characterization technique is used 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 MAPbI3films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI2added 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 PbI2must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI3optoelectronic properties as elucidated by the new CRPH approach.
Inorganic CsPbIBr2perovskites have recently attracted enormous attention as a viable alternative material for optoelectronic applications due to their higher efficiency, thermal stability, suitable bandgap, and proper optical absorption. However, the CsPbIBr2perovskite films fabricated using a one-step deposition technique is usually comprised of small grain size with a large number of grain boundaries and compositional defects. In this work, silver iodide (AgI) will be incorporated as an additive into the CsPbIBr2perovskite precursor solution to prepare the unique perovskite CsI(PbBr2)1-
- PAR ID:
- 10366962
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In the past years, hybrid perovskite materials have attracted great attention due to their superior optoelectronic properties. In this study, the authors report the utilization of cobalt (Co2+) to partially substitute lead (Pb2+) for developing novel hybrid perovskite materials, CH3NH3Pb1‐
x Cox I3(wherex is nominal ratio,x = 0, 0.1, 0.2 and 0.4). It is found that the novel perovskite thin films possess a cubic crystal structure with superior thin film morphology and larger grain size, which is significantly different from pristine thin film, which possesses the tetragonal crystal structure, with smaller grain size. Moreover, it is found that the 3d orbital of Co2+ensures higher electron mobilities and electrical conductivities of the CH3NH3Pb1‐x Cox I3thin films than those of pristine CH3NH3Pb4thin film. As a result, a power conversion efficiency of 21.43% is observed from perovskite solar cells fabricated by the CH3NH3Pb0.9Co0.1I3thin film. Thus, the utilization of Co, partially substituting for Pb to tune physical properties of hybrid perovskite materials provides a facile way to boost device performance of perovskite solar cells. -
Abstract State‐of‐the‐art perovskite solar cells (PSCs) have bandgaps that are invariably larger than 1.45 eV, which limits their theoretically attainable power conversion efficiency. The emergent mixed‐(Pb, Sn) perovskites with bandgaps of 1.2–1.3 eV are ideal for single‐junction solar cells according to the Shockley–Queisser limit, and they have the potential to deliver higher efficiency. Nevertheless, the high chemical activity of Sn(II) in these perovskites makes it extremely challenging to control their physical properties and chemical stability, thereby leading to PSCs with relatively low PCE and stability. In this work, the authors employ the Lewis‐adduct SnF2·3FACl additive in the solution‐processing of ideal‐bandgap halide perovskites (IBHPs), and prepare uniform large‐grain perovskite thin films containing continuously functionalized grain boundaries with the stable SnF2phase. Such Sn(II)‐rich grain‐boundary networks significantly enhance the physical properties and chemical stability of the IBHP thin films. Based on this approach, PSCs with an ideal bandgap of 1.3 eV are fabricated with a promising efficiency of 15.8%, as well as enhanced stability. The concept of Lewis‐adduct‐mediated grain‐boundary functionalization in IBHPs presented here points to a new chemical route for approaching the Shockley–Queisser limit in future stable PSCs.
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Inorganic−organic hybrid perovskites MAPb(I
x Br1−x )3(0 <x < 1) hold promise for efficient multi‐junction or tandem solar cells due to tunable bandgap and improved long‐term stability. However, the phase transformation from Pb(Ix Br1−x )2precursors to perovskites is not fully understood which hinders further improvement of optoelectronic properties and device performance. Here, adaptation of the two‐step deposition method, which enables the direct probe into the growth dynamics of perovskites using in situ diagnostics, and a detailed view of the effects of solvent, lead halide film solvation, and Br incorporation and alloying on the transformation behavior is presented. The in situ measurements indicate a strong tendency of lead halide solvation prior to crystallization during solution‐casting Pb(Ix Br1−x )2precursor from a dimethyl sulfoxide (DMSO) solvent. Highly‐efficient intramolecular exchange is observed between DMSO molecules and organic cations, leading to room‐temperature conversion of perovskite and high‐quality films with tunable bandgap and superior optoelectronic properties in contrast to that obtained from crystalline Pb(Ix Br1−x )2. The improved properties translate to easily tunable and a relatively higher power conversion efficiency of 16.42% based on the mixed‐halide perovskite MAPb(I0.9Br0.1)3. These findings highlight the benefits that solvation of the precursor phases, together with bromide incorporation, can have on the microstructure, morphology, and optoelectronic properties of these films. -
Abstract Intrinsically, detrimental defects accumulating at the surface and grain boundaries limit both the performance and stability of perovskite solar cells. Small molecules and bulkier polymers with functional groups are utilized to passivate these ionic defects but usually suffer from volatility and precipitation issues, respectively. Here, starting from the addition of small monomers in the PbI2precursor, a polymerization‐assisted grain growth strategy is introduced in the sequential deposition method. With a polymerization process triggered during the PbI2film annealing, the bulkier polymers formed will be adhered to the grain boundaries, retaining the previously established interactions with PbI2. After perovskite formation, the polymers anchored on the boundaries can effectively passivate undercoordinated lead ions and reduce the defect density. As a result, a champion power conversion efficiency (PCE) of 23.0% is obtained, together with a prolonged lifetime where 85.7% and 91.8% of the initial PCE remain after 504 h continuous illumination and 2208 h shelf storage, respectively.