{"id":2425,"date":"2026-05-25T11:34:10","date_gmt":"2026-05-25T11:34:10","guid":{"rendered":"https:\/\/www.thefullerene.com\/?p=2425"},"modified":"2026-05-26T13:25:13","modified_gmt":"2026-05-26T13:25:13","slug":"fullerenes-perovskite-solar-cells-interfacial-engineering","status":"publish","type":"post","link":"https:\/\/www.thefullerene.com\/ja\/fullerenes-perovskite-solar-cells-interfacial-engineering\/","title":{"rendered":"\u30da\u30ed\u30d6\u30b9\u30ab\u30a4\u30c8\u592a\u967d\u96fb\u6c60\u306b\u304a\u3051\u308b\u30d5\u30e9\u30fc\u30ec\u30f3\uff1a\u5206\u5b50\u30e1\u30ab\u30cb\u30ba\u30e0\u3001\u754c\u9762\u5de5\u5b66\u3001\u304a\u3088\u3073\u6b21\u4e16\u4ee3\u5149\u8d77\u96fb\u529b\u6280\u8853"},"content":{"rendered":"\n

In the rapidly evolving landscape of clean energy, metal halide perovskite solar cells (PSCs) have emerged as a highly disruptive alternative to conventional silicon photovoltaics, demonstrating a meteoric rise in certified power conversion efficiency (PCE) from 3.8% to over 27.0% in less than two decades. To validate the real-world operational viability of this technology, the Japanese government has launched a landmark, government-led demonstration project scheduled to begin in the summer of 2026. This pilot program involves the large-scale deployment of lightweight, flexible perovskite solar cells across various Self-Defense Forces (SDF) facilities, commencing at bases in Okinawa Prefecture. By installing these thin-film modules on diverse building walls and roofs where rigid silicon panels are physically unviable, the project aims to verify the cells’ long-term durability in complex, humid maritime environments and secure energy independence for critical national security infrastructure.<\/p>\n\n\n\n

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As perovskites transition from laboratory scale to strategic, high-exposure outdoor deployments, the optimization of their internal interfaces represents the most critical barrier to commercialization.<\/sup> In inverted (p-i-n) planar heterojunction configurations\u2014the preferred architecture for tandem integration and roll-to-roll manufacturing due to low-temperature processing and hysteresis-free charge collection\u2014the electron transport layer (ETL) largely dictates both the efficiency and lifetime of the device. Unmodified Carbon 60 (C60<\/a>) and its soluble derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have become the undisputed standard interfacial materials to maximize electron extraction and suppress non-radiative recombination.<\/p>\n\n\n\n

1. Quantum Dynamics and Isotropic Transport of Fullerenes<\/h2>\n\n\n\n

The dominance of fullerenes as n-type semiconductors in thin-film photovoltaics is fundamentally rooted in their molecular geometry and electronic structure.<\/sup> Unlike planar organic molecules that exhibit highly anisotropic charge transport dependent on face-to-face stacking orientations, the three-dimensional spheroidal conjugation of the C60<\/a> carbon cage allows for completely isotropic electron transport.<\/sup> Electrons can tunnel or “hop” with equal probability in any direction across the fullerene domains.<\/p>\n\n\n\n

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Furthermore, fullerenes exhibit an exceptionally low reorganization energy following electron transfer.<\/sup> This minimised thermodynamic barrier permits ultrafast electron extraction kinetics at the perovskite\/ETL interface. In a typical planar cell, the rate constant of photoinduced electron transfer ($k_{ET}$) can be modeled using the semiclassical Marcus equation:<\/p>\n\n\n\n

k<\/mi>E<\/mi>\u2062<\/mo>T<\/mi><\/mrow><\/msub>=<\/mo>2<\/mn>\u2062<\/mo>\u03c0<\/mi><\/mrow>\u210f<\/mi><\/mfrac>\u2062<\/mo>|<\/mo>V<\/mi>|<\/mo><\/mrow>2<\/mn><\/msup>\u2062<\/mo>(<\/mo>F<\/mi>\u2061<\/mo>C<\/mi>\u2062<\/mo>W<\/mi>\u2062<\/mo>D<\/mi>\u2062<\/mo>S<\/mi><\/mrow><\/mrow>)<\/mo><\/mrow><\/mrow><\/math><\/p>\n\n\n\n

Where $\\hbar$ is the reduced Planck constant, $V$ represents the electronic coupling matrix element between the perovskite donor and the fullerene acceptor, and $FCWDS$ is the Franck-Condon weighted density of states.<\/sup> The $FCWDS$ is mathematically defined by the reorganization energy ($\\lambda$) and the thermodynamic driving force ($-\\Delta G$):<\/p>\n\n\n\n

F<\/mi>(<\/mo>\u03bb<\/mi>,<\/mo>T<\/mi>)<\/mo>=<\/mo>(<\/mo>4<\/mn>\u03c0<\/mi>\u03bb<\/mi>k<\/mi>B<\/mi><\/msub>T<\/mi>)<\/mo>-1<\/mn>\/<\/mo>2<\/mn><\/mrow><\/msup>exp<\/mi>(<\/mo>\u2212<\/mo>\u2026<\/mo>4<\/mn>\u03bb<\/mi>k<\/mi>B<\/mi><\/msub>T<\/mi><\/mrow><\/mfrac>)<\/mo><\/mrow><\/mrow>cap F open paren lambda comma cap T close paren equals open paren 4 pi lambda k sub cap B cap T close paren raised to the negative 1 \/ 2 power exp open paren negative the fraction with numerator \u2026 and denominator 4 lambda k sub cap B cap T end-fraction close paren<\/annotation><\/semantics><\/math><\/p>\n\n\n\n

Because $\\lambda$ remains remarkably small in fullerenic systems, electron extraction occurs on a sub-picosecond timescale <\/sup>, effectively outcompeting geminate and non-geminate charge carrier recombination. This rapid charge transfer facilitates an efficient charge redistribution at the heterointerface, converting the contact into a highly selective n-type junction that blocks minority carrier holes while collecting majority carrier electrons.<\/p>\n\n\n\n

2. Interfacial Engineering: Passivating Surface Trap States<\/h2>\n\n\n\n

Despite the fast charge extraction mediated by pristine fullerenes, inverted planar PSCs are still limited by non-radiative recombination losses at the perovskite surface and across the perovskite\/C60<\/a> interface. The surface of polycrystalline perovskite films is inherently populated with localized electronic defects, dominated by halide vacancies, undercoordinated Pb2+ centers, and Pb-I antisites.<\/sup> These surface trap states serve as non-radiative recombination pathways, contributing to severe thermal losses that suppress the open-circuit voltage (Voc) of the device.<\/sup><\/p>\n\n\n\n

To neutralize these active defects, researchers employ multifunctional molecular bridging agents to passivate the perovskite surface while reorganizing the interfacial energetics.<\/p>\n\n\n\n

Dual-Site Molecular Bridging (DSA)<\/h3>\n\n\n\n

A prominent example is the use of (benzhydrylthio)acetic acid (DSA) to engineer the heterointerface between the perovskite and the PCBM layer. DSA establishes a highly stable molecular-bridging layer through dual-site anchoring. The thioether and carboxylic acid groups of the DSA molecules form strong coordinate covalent bonds with the undercoordinated Pb2+ defect sites, chemically passivating the surface traps. Concurrently, the hydrophobic benzhydryl segment of DSA participates in robust $\\pi$-$\\pi$ stacking with the overlying PCBM domain. The electron donation from the thioether moiety induces n-type band bending in the perovskite layer, upshifting its Fermi level and creating an enhanced internal electric field that significantly accelerates electron-extraction kinetics.<\/p>\n\n\n\n

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Interfacial Energetics Reconstruction (NMePS)<\/h3>\n\n\n\n

Similarly, the novel organic bridge NMePS has been designed to reconstruct the surface energetics of inverted PSCs. By tailoring the electronic states at the interface, NMePS drastically reduces the trap state density and yields a highly uniform perovskite surface morphology that is exceptionally receptive to subsequent C60 vacuum deposition. Small-area devices (0.045 cm2) modified with NMePS have achieved a remarkable power conversion efficiency of 26.87%, while larger-area sub-modules (1.00 cm2) maintained a highly stable efficiency of 25.06%. These modified systems exhibit exceptional operational durability, retaining 90% of their initial performance after more than 2,600 hours of continuous tracking.<\/p>\n\n\n\n

Three-Dimensional Aromatic Passivation (Ortho-Carborane)<\/h3>\n\n\n\n

To completely eradicate interfacial losses, researchers have introduced phenylamino-functionalized ortho-carborane as an ultrathin interlayer between the perovskite and the top C60 ETL. Ortho-carborane possesses a unique three-dimensional spherical aromaticity. The phenylamino groups coordinate with the perovskite surface to passivate defects, while the carborane core acts as a high-mobility electron-transporting and hole-blocking buffer. This dual passivation and blocking mechanism essentially eliminates the interfacial non-radiative recombination, delivering a certified PCE of over 23.0% with an exceptionally low non-radiative voltage loss of only 110 mV. Modified devices retain over 97% of their initial efficiency after 400 hours of continuous maximum power point tracking (MPPT) under simulated solar light.<\/p>\n\n\n\n

3. Cross-Linkable Fullerene Interlayers<\/h2>\n\n\n\n

The fabrication of high-performance p-i-n planar PSCs requires sequential layer-by-layer deposition. This architecture presents a significant processing challenge: when the active perovskite precursor solution is spin-cast, the polar organic solvents required to dissolve the perovskite precursors\u2014most notably dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)\u2014can wash away or erode the underlying electron-transporting fullerene interlayer.<\/p>\n\n\n\n

To address this solvent erosion, scientists have synthesized thermally and photochemically cross-linkable fullerene derivatives. Two key derivatives include:<\/p>\n\n\n\n