Yoyo Hinuma

A recent advancement in perovskite solar cells (PSCs) is the emergence of spontaneous heterointerface modulators (SHMs), which eliminate the additional processing required for conventional heterointerface modification. Among SHMs, alkyl‐primary‐ammonium‐bis(trifluoromethylsulfonyl)imides (RA‐TFSIs), used as hole‐transport material (HTM) additives, enable spontaneous perovskite passivation. Upon HTM deposition, RA cations passivate the perovskite surface through strong adsorption via the ammonium (NH ₃ ⁺ ) moiety. However, conventional RA‐TFSIs only passivate A ‐site defects, limiting their effectiveness. Moreover, RA components with multiple functional groups have not been explored. Here, we propose a strategy to suppress multiple defect sites using a spontaneous passivator with dual functional groups. 2‐thiophene‐ethyl‐ammonium‐TFSI (TEA‐TFSI) is newly synthesized and verified as a spontaneous perovskite passivator for n–i–p PSCs employing thermally stable poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) as the HTM. Spontaneous passivation using TEA‐TFSI forms a monolayer‐like overlayer, where TEA cations are adsorbed at both A ‐ and X ‐site defects via ammonium and thiophene moieties, respectively, overcoming the single‐site limitation of RA‐TFSIs. The TEA overlayer also improves PTAA adhesion. Consequently, PSCs achieve power conversion efficiencies of 22.2% (≈0.12 cm ² minicells) and 21.7% (≈1.6 cm ² minimodules, active area: 1.41 cm ² ), respectively, with thermal stability. This work establishes a general design principle for multifunctional spontaneous passivators and advances materials science.

The thermal stability of perovskite solar cells (PSCs) remains a critical challenge for their integration into power grid applications. Here, we report the thermally stable PSCs by employing heteroaryl additives in the Spiro-OMeTAD. These additives effectively control void formation in the hole-transport layer and minimize reactivity with the perovskite layer, significantly improving the thermal stability of PSCs at 85 °C. As a result, PSCs with 3-phenylpyridine and 2-phenylpyridine maintained 101% and 104% of their initial photoconversion efficiency after 2400 hours of 85 °C test, respectively. As an added benefit, photovoltaic performance achieved a photoconversion efficiency of 25%. Also, the outdoor test shows 90% of the initial power point voltage after 1570 hours with maximum-power point tracking, showing remarkable light and cycle stability. We revealed the mechanism of how the additive can improve the thermal stability of PSCs by comparing 36 heteroaryl derivatives and 60 additive combinations.

The structure and charge/discharge mechanism of an Fe-containing Li ₂ S-based positive electrode material (Li ₈ FeS ₅ ) were investigated using X-ray scattering and absorption spectroscopy analyses.

Amaterasuite [(SrxBa1-x)4Ti6Si4O23(OH)Cl] is a jadeitite mineral with a dual nature encapsulating two sets of atom sites. The sets of atom sites are not equivalent; 85% of the crystal is in one set and 15% is in the other, and the Sr:Ba ratio differs between the two sets. Universal neural network potential calculations were performed to evaluate defect formation energies. Amaterasuite favors phase separation into the end members (x = 0 and 1); however, if this is not allowed in a single particle, some phase boundaries (PBs), which separate regions with different Sr:Ba ratios, form with almost no energy penalty. Thus, no strong driving force exists to segregate Sr and Ba once the local Sr:Ba ratio is determined during formation. Stacking fault (SF) formation energies normal to the c axis are sufficiently low to form spontaneous SFs, and SFs preferentially form next to each other. The SF direction differs from the low-formation-energy PB directions. This complexity can explain the coexistence of two sets of atom sites and the possibility of regions with different Sr:Ba ratios, although the difference in average Sr:Ba ratios between the two sets of atom sites is not anticipated from the calculations.

The mechanisms regarding 4- tert -butylpridine ( t BP) coordination to alkylammoniums via hydrogen bonding are revealed by both theoretical and experimental investigations, plugging a key knowledge gap in the research field of perovskite solar cells.

Alkylammonium bis(trifluoromethanesulfonyl)imide (RA-TFSI) ionic liquids (ILs) have recently emerged as reactive ILs and exhibit prominent reactivities that differ from those of conventional ILs. RA-TFSIs exhibit unique functions for incorporation into perovskite solar cells (PSCs), exploiting high reactivity of RA cations to perovskite layer; they are used as additives for hole-transport materials (HTMs) and exhibit spontaneous perovskite passivation. During the deposition of an RA-TFSI-containing HTM solution, the RA cations spontaneously passivate the perovskite structure, exploiting the large adsorption energy of the RA cations on the perovskite surface. Thus, the use of RA-TFSIs avoids an additional perovskite passivation process, and shows promise for replacing Li-TFSI, which is most commonly used yet known to be detrimental to PSCs. However, reactive ILs are still in their infancy, and establishing methods for controlling their reactivity is essential for advancing spontaneous perovskite passivation techniques and exploring novel applications of emerging reactive ILs. In this study, a novel strategy is proposed to tune the reactivities of reactive ILs by modulating the class of alkylammonium incorporated into the RA-TFSIs. A series of RA-TFSIs with varied classes of alkylammoniums were newly prepared, which is the first series of alkylammonium class modulation in reactive ILs and RA-TFSIs, and their functions as spontaneous perovskite passivators are verified. When moving from tertiary to secondary and primary alkylammonium classes, the reactivities of the RA cations were enhanced; their adsorption energies on the perovskite surface increased (i.e., their adsorption energies became more exothermic). The resulting increase in RA-TFSI reactivity with decreasing alkylammonium class led to more effective spontaneous perovskite passivation, thereby enhancing the photovoltaic performance of the PSCs. This work demonstrates successful reactivity control in reactive ILs, thereby spurring the exploration of novel applications and ultimately contributing to further advancements in materials science.

A recent and potent advancement in perovskite solar cells (PSCs) is the emergence of spontaneous heterointerface modulators (SHMs), which bypasses the required additional processes of conventional heterointerface modulations. Among SHMs, alkyl-primary-ammonium-bis(trifluoromethylsulfonyl)imides (RA-TFSIs), used as hole–transport material (HTM) additives, exhibit spontaneous perovskite passivation. Upon deposition of the HTM solution containing the RA-TFSI additive, the RA cations spontaneously passivate the perovskite, exploiting the high adsorption energy of RA cations via its ammonium moiety (NH3+) over the perovskite surface. However, conventional RA-TFSIs passivate only A-site defects in perovskite crystals due to their specific passivation mechanism, which limits their effectiveness and is an intrinsic drawback of RA-TFSIs so far. Moreover, the RA components thus far have been limited; those with multiple functional groups are unprecedented. In this work, we propose a novel strategy for suppressing multiple defect sites using a spontaneous perovskite passivator featuring dual functional groups. 2-thiophene-ethyl-ammonium-TFSI (TEA-TFSI) was newly synthesized and verified as a spontaneous perovskite passivator for n-i-p-structured PSCs employing thermally stable poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) HTM. Spontaneous perovskite passivation using the TEA-TFSI HTM additive formed a monolayer-like passivation overlayer, unlike that in conventional TEA-based passivators. The TEA cation exhibited dual-site adsorption on A-site and X-site defects via attachments of ammonium and thiophene moieties, respectively, effectively overcoming the single-site limitation of conventional RA-TFSIs. Beyond defect suppression, the TEA overlayer enhanced the physical attachment of PTAA on the perovskite. As a result, the TEA-TFSI HTM additive enhanced the photovoltaic performance of PSCs with thermal stability owing to spontaneous perovskite passivation and thereby achieved power conversion efficiency up to 22.2% and 21.7% for minicells (≈0.12 cm2) and minimodules (≈1.6 cm2, active area: 1.41 cm2), respectively. This study demonstrates a generalizable design principle for multifunctional spontaneous passivators and provides novel insights into SHM engineering for PSCs.

Hydrogen absorption and desorption in solids are pivotal reactions involved in batteries and hydrogen storage devices. However, conventional thermodynamic and electrochemical hydrogen storage using high-capacity materials suffers from high hydrogen-desorption temperatures and instability of electrolytes. In this work, we explored electrochemical hydride ion (H ^– )–driven hydrogen storage and developed a solid electrolyte, anti–α-AgI–type Ba _0.5 Ca _0.35 Na _0.15 H _1.85 , which exhibits excellent H ^– conductivity and electrochemical stability. This electrolyte is compatible with several metal-hydrogen electrodes, such as titanim hydride and magnesium hydride (MgH ₂ ), allowing for high-capacity, reversible hydrogen storage at low temperatures. Specifically, Mg–H ₂ cells operating as hydrogen storage devices (Mg + H ₂ ⇄ MgH ₂ ) achieved a reversible capacity of 2030 milliampere hours per gram at 90°C, offering safe and efficient hydrogen-electricity conversion and hydrogen storage devices.

Perovskite solar cells (PSCs) have advanced rapidly; however, the typical set of additives for hole transport materials (HTMs), including 4-tert-butylprydine (tBP), is still commonly used ever since the discovery of the first solid-state PSCs, regardless of its potential negative effects. The tBP is considered detrimental to PSCs because it can react with perovskite crystals. In particular, the reactions between tBP and the Pb2+ cation, a perovskite component, have been well acknowledged. In contrast, the interactions between tBP and alkylammoniums, another perovskite component, has sparsely been investigated despite the widespread use of tBP, hindering the development of PSCs. In this work, the mechanisms of interactions between tBP and alkylammoniums are revealed via theoretical studies. In the case of n-octylammonium (OA), up to three tBP molecules stabilize the ammonium moiety in OA via coordination with strong hydrogen bonding between the nitrogen in tBP and hydrogen in the ammonium moiety of OA. Up to three more tBP molecules can coordinate via weak hydrogen bonding to already coordinated tBP molecules. Leveraging this characteristic, herein, the mechanism of spontaneous perovskite passivation is investigated using an HTM solution containing tBP and an OA-based additive (OA-TFSI). The OA unit coordinated to 3 tBP molecules was found to directly chemisorb on the perovskite surface. However, the revealed chemisorption led to the formation of substantial physical space between OA and the perovskite surface, impeding hole injection from the perovskite to HTM. Finally, a method to address this issue is experimentally demonstrated: post-heating removed the coordination of bulky tBP molecules, facilitating hole injection via close adsorption of solo OA cations on the perovskite surface, enhancing the photovoltaic performance of PSCs. This study provides profound insights into the tBP effects, an unexplored aspect in PSC studies, as well as the nascent yet potent spontaneous perovskite passivation techniques.