Dion-Jacobson and Ruddlesden-Popper double-phase 2D perovskites for solar cells

Dion-Jacobson (DJ) phase and Ruddlesden-Popper phase 2D perovskites have been, individually, demonstrated to be more stable than 3D counterparts for perovskite solar cells (PSCs). In order to further improve the efficiency and stability of 2D PSCs, we herein report merging them to construct a DJ:RP double-phase perovskite (DPP) structure for the first time. With the DJ 2D perovskite composed of diammonium as the matrix, a monoammonium with a larger size than the diammonium is incorporated to form an independent RP phase 2D perovskite coexisting with the DJ one (DJ:RP DPP structure), which facilitates crystal growth, suppresses charge recombination, and improves charge transport. As a comparison, introduction of a smaller monoammonium than the diammonium leads to its insertion between inorganic slabs, yielding a distorted DJ 2D perovskite structure, which induces lattice relaxation/distortion and thus lowered charge transportation. Consequently, 2D PSCs based on the DJ:RP DPP afford an impressive efficiency of 13.8% with excellent thermal stability at 85 degrees C in damp air. This work demonstrates a new and promising strategy of developing the DJ:RP DPP for highly efficient and robust 2D PSCs.

Investigation in Crystal Growth/Morphology and Interface Engineering of Perovskite Solar Cells by Different Deposition Methods

Nadja Isabelle Desiree Klipfel

A new and promising technology has emerged to compete with traditional silicon photovoltaic semiconductors. The low material and processing costs and high-power conversion efficiencies of organic-inorganic metal halide perovskites make these a promising technology for the future. Despite record efficiencies for small-area devices, stability remains challenging. Due to rapid progress in the field, avenues for large-area commercial production are being explored. One approach is via thermal evaporation, which is presented in this work. The focus is on the vacuum-deposition method itself, the interface engineering of perovskite layers, and the study of a family of low-cost hole-transporting materials (HTM). To improve reproducibility among research groups in vacuum-deposition processes, a better understanding and control of the crystal formation is essential. Of the experimental parameters, two were investigated that were not yet considered in-depth or combined: deposition speed and underlayer material. It was shown that perovskite growth rate changes affect preferred crystal orientation. In addition, it was found that the final perovskite composition is influenced by its underlayer chemistry. Multi-source vacuum deposition of perovskite layers is complex due to the laborious calibration process necessary for proper stoichiometry. Single-source evaporation of pre-synthesized perovskite powders can reduce effort and time. The feasibility of obtaining pure phase films was demonstrated and confirmed by multiple analysis methods.Interfaces in contact with the perovskite can be a source of defects with a deteriorating effect on stability and efficiency. The charge transport processes at the interface of electron transport material (ETM) and perovskite were investigated. The results showed a synergetic effect between cTiO2 and C60 and the importance of C60 as a charge extraction layer. The perovskite hole transporting material (HTM) interface was also systematically studied. Monitoring of dopants showed, for the first time in literature, TFSI anion migration through grain boundaries to the perovskite surface. It was further shown that non-radiative recombination pathways are reduced, indi-cating self-passivating of crystal defects during migration processes.The state-of-the-art HTM 2,2',7,7'-tetrakis (N,N-di-p-methoxyphenylamine)-9,9'spirofluorene (spiro-OMeTAD) is widely employed in spin-coated PSCs. Devel-oping a less costly manufacturing alternative to this material that retains similar properties is a key challenge. A new class of Zn (II) and Cu (II)-based phthalocyanine HTMs functionalized with butyl- and ethylhexyl- groups in the periphery was investigated. Devices fabricated with the Zn (II)-based HTM (n-butyl functionalization) demonstrated the best performance. The device architecture with the highest stability maintained 80% of its initial power conversion efficiency (PCE) over 20h of illumination. At 20.2%, the perovskite architecture with the highest PCE also was the least stable, indicating a trade-off between these two characteristics for this HTM class.

EPFL2022

Silicon Heterojunction Solar Cells on Quasi-mono Wafers

Brahim Aissa, Christophe Ballif, Loris Barraud, Mathieu Gérard Boccard, Antoine Descoeudres, Matthieu Despeisse, Jan Haschke, Raphaël Monnard

We applied hydrogen passivation, gettering and a combination of both to quasi-mono (qm) wafer material to enhance its bulk lifetime and prepared silicon heterojunction (SHJ) solar cells. We find that while our applied hydrogen passivation alone seems not to enhance lifetime, a gettering treatment increases bulk lifetime so that efficiencies up to 21.5% were achieved with a SHJ solar cell. This is close to the highest efficiency reported for such a cell. We find that the variation of the absorber thickness plays a minor role for the investigated solar cells and that similar efficiencies could have been obtained for Cz and gettered qm wafers. The latter is mainly due to the fact that the higher efficiency potential of the Cz material could not be fully exploited due to a degradation of surface passivation during the sputtering of the TCO on the cell, which could not be fully recovered in the final annealing step.

IEEE2018

High-Performance Flexible All-Perovskite Tandem Solar Cells with Reduced V-OC-Deficit in Wide-Bandgap Subcell

Fan Fu, Quentin Thomas Jeangros, Jarla Thiesbrummel

Among various types of perovskite-based tandem solar cells (TSCs), all-perovskite TSCs are of particular attractiveness for building- and vehicle-integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power-to-weight ratio. However, the efficiency of flexible all-perovskite tandems is lagging far behind their rigid counterparts primarily due to the challenges in developing efficient wide-bandgap (WBG) perovskite solar cells on the flexible substrates as well as their low open-circuit voltage (V-OC). Here, it is reported that the use of self-assembled monolayers as hole-selective contact effectively suppresses the interfacial recombination and allows the subsequent uniform growth of a 1.77 eV WBG perovskite with superior optoelectronic quality. In addition, a postdeposition treatment with 2-thiopheneethylammonium chloride is employed to further suppress the bulk and interfacial recombination, boosting the V-OC of the WBG top cell to 1.29 V. Based on this, the first proof-of-concept four-terminal all-perovskite flexible TSC with a power conversion efficiency of 22.6% is presented. When integrating into two-terminal flexible tandems, 23.8% flexible all-perovskite TSCs with a superior V-OC of 2.1 V is achieved, which is on par with the V-OC reported on the 28% all-perovskite tandems grown on the rigid substrate.

WILEY-V C H VERLAG GMBH2022

Investigation in Crystal Growth/Morphology and Interface Engineering of Perovskite Solar Cells by Different Deposition Methods

Nadja Isabelle Desiree Klipfel

EPFL2022