Atomistic understanding of the coherent interface between lead iodide perovskite and lead iodide

Advanced Materials Interfaces Wiley 10:28 (2023) 2300249

Authors:

Mathias Uller Rothmann, Kilian B Lohmann, Juliane Borchert, Michael B Johnston, Keith P McKenna, Laura M Herz, Peter D Nellist

Abstract:

Metal halide perovskite semiconductors have shown great performance in solar cells, and including an excess of lead iodide (PbI2) in the thin films, either as mesoscopic particles or embedded domains, often leads to improved solar cell performance. Atomic resolution scanning transmission electron microscope micrographs of formamidinium lead iodide (FAPbI3) perovskite films reveal the FAPbI3:PbI2 interface to be remarkably coherent. It is demonstrated that such interface coherence is achieved by the PbI2 deviating from its common 2H hexagonal phase to form a trigonal 3R polytype through minor shifts in the stacking of the weakly van-der-Waals-bonded layers containing the near-octahedral units. The exact crystallographic interfacial relationship and lattice misfit are revealed. It is further shown that this 3R polytype of PbI2 has similar X-ray diffraction (XRD) peaks to that of the perovskite, making XRD-based quantification of the presence of PbI2 unreliable. Density functional theory demonstrates that this interface does not introduce additional electronic states in the bandgap, making it electronically benign. These findings explain why a slight PbI2 excess during perovskite film growth can help template perovskite crystal growth and passivate interfacial defects, improving solar cell performance.

Organic copolymer lasing from single defect microcavity fabricated using laser patterning

Journal of Materials Chemistry C Royal Society of Chemistry (RSC) 11:24 (2023) 8204-8213

Authors:

Peter Claronino, Rahul Jayaprakash, Till Jessewitsch, Rachel C Kilbride, Timothy Thornber, Alina Muravitskaya, Robert DJ Oliver, Ullrich Scherf, Jean-Sebastien G Bouillard, Ali M Adawi, David G Lidzey

Photovoltaic performance of FAPbI3 perovskite is hampered by intrinsic quantum confinement

ACS Energy Letters American Chemical Society 8:6 (2023) 2543-2551

Authors:

Karim A Elmestekawy, Benjamin M Gallant, Adam D Wright, Philippe Holzhey, Nakita K Noel, Michael B Johnston, Henry J Snaith, Laura M Herz

Abstract:

Formamidinium lead trioiodide (FAPbI3) is a promising perovskite for single-junction solar cells. However, FAPbI3 is metastable at room temperature and can cause intrinsic quantum confinement effects apparent through a series of above-bandgap absorption peaks. Here, we explore three common solution-based film-fabrication methods, neat N,N-dimethylformamide (DMF)–dimethyl sulfoxide (DMSO) solvent, DMF-DMSO with methylammonium chloride, and a sequential deposition approach. The latter two offer enhanced nucleation and crystallization control and suppress such quantum confinement effects. We show that elimination of these absorption features yields increased power conversion efficiencies (PCEs) and short-circuit currents, suggesting that quantum confinement hinders charge extraction. A meta-analysis of literature reports, covering 244 articles and 825 photovoltaic devices incorporating FAPbI3 films corroborates our findings, indicating that PCEs rarely exceed a 20% threshold when such absorption features are present. Accordingly, ensuring the absence of these absorption features should be the first assessment when designing fabrication approaches for high-efficiency FAPbI3 solar cells.

Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells

Nature Energy Springer Nature 8:5 (2023) 462-472

Authors:

Xiaopeng Zheng, Zhen Li, Yi Zhang, Min Chen, Tuo Liu, Chuanxiao Xiao, Danpeng Gao, Jay B Patel, Darius Kuciauskas, Artiom Magomedov, Rebecca A Scheidt, Xiaoming Wang, Steven P Harvey, Zhenghong Dai, Chunlei Zhang, Daniel Morales, Henry Pruett, Brian M Wieliczka, Ahmad R Kirmani, Nitin P Padture, Kenneth R Graham, Yanfa Yan, Mohammad Khaja Nazeeruddin, Michael D McGehee, Zonglong Zhu, Joseph M Luther

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.

Journal of the American Chemical Society American Chemical Society (ACS) 145:18 (2023) 10275-10284

Authors:

Elisabeth A Duijnstee, Benjamin M Gallant, Philippe Holzhey, Dominik J Kubicki, Silvia Collavini, Bernd K Sturdza, Harry C Sansom, Joel Smith, Matthias J Gutmann, Santanu Saha, Murali Gedda, Mohamad I Nugraha, Manuel Kober-Czerny, Chelsea Xia, Adam D Wright, Yen-Hung Lin, Alexandra J Ramadan, Andrew Matzen, Esther Y-H Hung, Seongrok Seo, Suer Zhou, Jongchul Lim, Thomas D Anthopoulos, Marina R Filip, Michael B Johnston

Abstract:

Formamidinium lead triiodide (FAPbI<sub>3</sub>) is the leading candidate for single-junction metal-halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl<sub>2</sub>) has been used as an additive in FAPbI<sub>3</sub>. MDA<sup>2+</sup> has been reported as incorporated into the perovskite lattice alongside Cl<sup>-</sup>. However, the precise function and role of MDA<sup>2+</sup> remain uncertain. Here, we grow FAPbI<sub>3</sub> single crystals from a solution containing MDACl<sub>2</sub> (FAPbI<sub>3</sub>-M). We demonstrate that FAPbI<sub>3</sub>-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA<sup>2+</sup> is not the direct cause of the enhanced material stability. Instead, MDA<sup>2+</sup> degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI<sub>3</sub> crystals grown from a solution containing HMTA (FAPbI<sub>3</sub>-H) replicate the enhanced α-phase stability of FAPbI<sub>3</sub>-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA<sup>+</sup> is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H<sup>+</sup>). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H<sup>+</sup> is selectively incorporated into the bulk of both FAPbI<sub>3</sub>-M and FAPbI<sub>3</sub>-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability.