Stable Inverted Perovskite Solar Cells Research Articles

Enhancing Efficiency and Stability of Inverted Perovskite Solar Cells through Solution‐Processed and Structurally Ordered Fullerene

AbstractThe electron transporting layer (ETL) used in high performance inverted perovskite solar cells (PSCs) is typically composed of C60, which requires time‐consuming and costly thermal evaporation deposition, posing a significant challenge for large‐scale production. To address this challenge, herein, we present a novel design of solution‐processible electron transporting material (ETM) by grafting a non‐fullerene acceptor fragment onto C60. The synthesized BTPC60 exhibits an exceptional solution processability and well‐organized molecular stacking pattern, enabling the formation of uniform and structurally ordered film with high electron mobility. When applied as ETL in inverted PSCs, BTPC60 not only exhibits excellent interfacial contact with the perovskite layer, resulting in enhanced electron extraction and transfer efficiency, but also effectively passivates the interfacial defects to suppress non‐radiative recombination. Resultant BTPC60‐based inverted PSCs deliver an impressive power conversion efficiency (PCE) of 25.3 % and retain almost 90 % of the initial values after aging at 85 °C for 1500 hours in N2. More encouragingly, the solution‐processed BTPC60 ETL demonstrates remarkable film thickness tolerance, and enables a high PCE up to 24.8 % with the ETL thickness of 200 nm. Our results highlight BTPC60 as a promising solution‐processed fullerene‐based ETM, opening an avenue for improving the scalability of efficient and stable inverted PSCs.

Polymerized non-fullerene small molecular acceptor as a versatile electron-transport material for 24.50 % efficiency inverted perovskite solar cells with extended spectral response

Development of novel non-fullerene electron-transport materials (ETMs) with excellent optoelectronic properties, good thermal and chemical stability, and defect passivation capability is of great significance for improving the device performance of inverted perovskite solar cells (PSCs). In this work, a polymerized non-fullerene small molecular acceptor with narrow bandgap named PY-DFT is rationally designed and synthesized. The resultant materials not only exhibits great hydrophobicity, thermal and chemical stability, but also maintains the excellent electron-transport properties of Y-type small molecule. Moreover, the electron-rich units in PY-DFT finely passivates the surface defects in perovskite. Consequently, an exceptional PCE of 24.50 % has been achieved for the champion device based on PY-DFT ETM, which is the highest efficiency for inverted PSCs based on non-fullerene ETMs to date. Notably, PY-DFT provides an extra current density of 0.25 mA/cm2 in the near-infrared light response region, where the intrinsic perovskite film has no spectral response, demonstrating attractive advantages in rationally utilization of solar spectrum. The target device without encapsulation also demonstrates good long-term operational stability. This work paves a new avenue for designing photo-active non-fullerene electron-acceptor towards efficient and stable inverted PSCs.

Efficient and stable inverted perovskite solar cells enabled by homogenized PCBM with enhanced electron transport

Fullerene derivatives are extensively employed in inverted perovskite solar cells due to their excellent electron extraction capabilities. However, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) agglomerates easily in solution and exhibits a relatively low ionization barrier, increasing charge recombination losses and charge accumulation in the interface. Here, tetramethylthiuram disulfide (TMDS) is introduced into the PCBM solution to induce the formation of reducing sulfur radicals through UV light irradiation, allowing for n doping of the PCBM material. The resulting modified PCBM layer exhibits enhanced conductivity and electron mobility, significantly suppressing charge recombination. As a result, the resulting devices incorporating TMDS achieve a champion efficiency of 26.10% (certified 25.39%) and 24.06% at a larger area (1.0 cm2) with negligible hysteresis. More importantly, the optimized devices retain 95% and 90% of their initial efficiency after 1090 h under damp heat testing (85 °C and 85% relative humidity) and after 1271 h under maximum power point-tracking conditions, respectively.

Vertically Oriented 2D Perovskite Layer with n = 1 Phase Enables Efficient and Stable Inverted Perovskite Solar Cells.

Surface passivation with 2D perovskites has been reported to be important for high-performance perovskite solar cells (PSCs). However, it is challenging to achieve a controlled growth of 2D perovskites, which typically feature random orientation and various n number. In this paper, we fabricate a 2D layer with a highly ordered orientation and pure n = 1 phase on top of the perovskite film using the organic spacer molecule 7-fluoro-1,2,3,4-tetrahydroisoquinolinehydrochloride (7-FTH). The formed 2D perovskites feature a highly ordered orientation normal to the substrate and a pure n = 1 phase, which efficiently passivates surface defects of the as-prepared perovskite films and improves the energy level alignment between the perovskite film and electron transport layer. Consequently, the modified PSCs achieve a champion power conversion efficiency (PCE) of 24.65% with improved VOC and fill factor. After being stored in an N2 glovebox for 1200 h and kept in ambient air (room temperature and relative humidity of 50-70%) for 840 h, the modified devices retain 93% and 95% of its initial PCE, respectively.

A Diphosphonic Acid-Based Interlayer for Highly Efficient and Stable Inverted Perovskite Solar Cells.

We investigate an interlayer of 6,6'-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-[1,1'-binaphthalene]-(2,2'-diyl)bis(oxy)bis(propane-3,1-diyl)bis(phosphonic acid) (BINOL-PA) with undoped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) coverage. The incorporation of the 1,10-bi-2-naphthol central core enhances π-π stacking and reduces charge recombination at the interface. Compared to PTAA alone (0.95 eV), BINOL-PA/PTAA exhibits a shorter distance from the Fermi energy (EF) to the valence-band maximum (VBM) (0.36 eV). Two phosphoric acid units in BINOL-PA fine-tune the molecular dipoles. Theoretical calculations reveal electrostatic surface potential differences between BINOL-PA and PTAA in their backbone structure. Open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) results suggest suppressed interface recombination. The photovoltaic conversion efficiency (PCE), short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) for the BINOL-PA/PTAA device are measured as 21.02%, 22.67 mA cm-2, 1.12 V, and 82.8%, respectively, all higher than those achieved by the PTAA device with a PCE of 18%. BINOL-PA/PTAA significantly elevates VOC and FF values compared with dopant-free PTAA alone. The champion device retains over 89% of its initial PCE after being exposed to an ambient environment without encapsulation for more than 30 days. The thermal aging test conducted under a nitrogen atmosphere demonstrates that the efficiency retention rate for BINOL-PA/PTAA displays 60% of its initial efficiency after 1500 h.

Self-Assembled Monolayer Hole Transport Layers for High-Performance and Stable Inverted Perovskite Solar Cells

Self-Assembled Monolayer Hole Transport Layers for High-Performance and Stable Inverted Perovskite Solar Cells

Cross-Linkable Fullerene Electron Transport Layer with Internal Encapsulation Capability for Efficient and Stable Inverted Perovskite Solar Cells.

A stable and compact fullerene electron transport layer (ETL) is crucial for high-performance inverted perovskite solar cells (PSCs). However, traditional fullerene-based ETLs like C60 and PCBM are prone to aggregate under operational conditions, a challenge recently recognized by academic and industrial researchers. Here, we designed and synthesized a novel cross-linkable fullerene molecule, bis((3-methyloxetan-3-yl)methyl) malonate-C60 monoadduct (BCM), for use as an ETL in PSCs. Upon a low-temperature annealing at 100 °C, BCM undergoes in-situ cross-linking to form a robust cross-linked BCM (CBCM) film, which demonstrates excellent electron mobility and a suitable band structure for efficient PSCs. Our results show that PSCs incorporating CBCM-based ETL achieve an impressive efficiency of 25.89% (certified: 25.36%), significantly surpassing the 23.25% efficiency of PCBM-based devices. The intramolecular covalent interactions within CBCM films effectively prevent aggregation and enhance film compactness, creating an internal encapsulation layer that mitigates the decomposition and ion migration of perovskite components. Consequently, CBCM-based PSCs show exceptional stability, maintaining 97.8% of their initial efficiency after 1000 hours of maximum power point tracking, compared to only 78.6% retention in PCBM-based devices after less than 820 hours.

Efficient and Stable Inverted Perovskite Solar Cells Enabled by a Fullerene‐Based Hole Transport Molecule

AbstractDesigning an efficient modification molecule to mitigate non‐radiative recombination at the NiOx/perovskite interface and improve perovskite quality represents a challenging yet crucial endeavor for achieving high‐performance inverted perovskite solar cells (PSCs). Herein, we synthesized a novel fullerene‐based hole transport molecule, designated as FHTM, by integrating C60 with 12 carbazole‐based moieties, and applied it as a modification molecule at the NiOx/perovskite interface. The in situ self‐doping effect, triggered by electron transfer between carbazole‐based moiety and C60 within the FHTM molecule, along with the extended π conjugated moiety of carbazole groups, significantly enhances FHTM's hole mobility. Coupled with optimized energy level alignment and enhanced interface interactions, the FHTM significantly enhances hole extraction and transport in corresponding devices. Additionally, the introduced FHTM efficiently promotes homogeneous nucleation of perovskite, resulting in high‐quality perovskite films. These combined improvements led to the FHTM‐based PSCs yielding a champion efficiency of 25.58 % (Certified: 25.04 %), notably surpassing that of the control device (20.91 %). Furthermore, the unencapsulated device maintained 93 % of its initial efficiency after 1000 hours of maximum power point tracking under continuous one‐sun illumination. This study highlights the potential of functionalized fullerenes as hole transport materials, opening up new avenues for their application in the field of PSCs.

A Surface-Reconstructed Bilayer Heterojunction Enables Efficient and Stable Inverted Perovskite Solar Cells.

The efficiency of perovskite photovoltaics remains distant from their theoretical limits, primarily due to high photovoltage losses. Here a strategy is reported to minimize voltage losses by reconstructing the perovskite surface into a bilayer heterojunction (BLH) structure. Unlike conventional low-dimensional capping layers, typically constrained to a few nanometers to prevent low fill factors, this methodology facilitates a more comprehensive reaction with surface defects, allowing a more substantial capping layer (≈50 nanometers) without compromising charge transport integrity. Time-resolved microwave conductivity analysis indicates a significant reduction in trap density at the top region of the perovskite film, showing an order of magnitude lower than that of the pristine sample. Incorporating this BLH in inverted cells results in a remarkably low photovoltage deficit of 325mV, leading to a power conversion efficiency (PCE) of 26.1% (25.72% certified). The encapsulated device maintains 94% of its original efficiency after 1200h of maximum power point tracking under one sun illumination at 65°C.

Molecularly tailored bifunctional nano-overlayers for efficient and stable inverted perovskite solar cells

Triple cation perovskite solar cells (PSCs) have made remarkable progress in power conversion efficiency (PCE), which is also related to the interface regulation layers between the active layer and electron transport layer (ETL). The ionic nature of the perovskite lattice has enabled approaches to passivate molecular defects through the interaction of functional groups. Herein, a passivator OXD-7 is introduced as a modified layer to passivate surface defects and accelerate electron transfer. It has been observed that OXD-7 can alleviate the micro-strain of the perovskite thin films through intermolecular bonding, which suppresses the iodide vacancy on the perovskite surface. Additionally, the OXD-7 reduces the surface energy of the perovskite films and inhibits the formation of δ-FAPbI3 on the surface of perovskite film. Consequently, the resulting devices demonstrate improved fill factor and device stability. Under optimal fabrication conditions, triple cation mixed perovskite solar cells with an inverted structure achieve a PCE of 23.83%.

Surface Lattice Engineering Enables Efficient Inverted Perovskite Solar Cells

AbstractState‐of‐the‐art inverted perovskite solar cells (PSCs) have exhibited considerable promise for commercialization due to their prospective stability. However, the intricate crystallization of halide perovskite, especially for multi‐component perovskites, not only distorts the surface lattice from its ideal form but also introduces numerous unsaturated dangling bonds to form surface defects, which can easily lead to reduced stability and poor performance. Herein, a surface lattice engineering is developed by coupling surface unsaturated ions and regulating ion bonding lengths/angles to achieve efficient and stable inverted PSCs. The renovated surface lattice not only eliminates shallow/deep level defects on the surface of perovskite, but also enhances photo/thermal stability of the materials. Moreover, the surface lattice engineering contributes to uniform potential surface, and improves energy‐level alignment at the interfaces of the perovskite and C60 carrier transport layer, enhancing charge carrier extraction and transportation. Finally, the champion PSC delivers an impressive efficiency of 25.82% (certified 25.5%). Moreover, these PSCs exhibit excellent operational stability, retaining 94% initial efficiency after more than ≈1 000h maximum power point test.

Enhancing Efficiency and Stability of Inverted Perovskite Solar Cells through Solution-Processed and Structurally Ordered Fullerene.

The electron transporting layer (ETL) used in high performance inverted perovskite solar cells (PSCs) is typically composed of C60, which requires time-consuming and costly thermal evaporation deposition, posing a significant challenge for large-scale production. To address this challenge, herein, we present a novel design of solution-processible electron transporting material (ETM) by grafting a non-fullerene acceptor fragment onto C60. The synthesized BTPC60 exhibits an exceptional solution processability and well-organized molecular stacking pattern, enabling the formation of uniform and structurally ordered film with high electron mobility. When applied as ETL in inverted PSCs, BTPC60 not only exhibits excellent interfacial contact with the perovskite layer, resulting in enhanced electron extraction and transfer efficiency, but also effectively passivates the interfacial defects to suppress non-radiative recombination. Resultant BTPC60-based inverted PSCs deliver an impressive power conversion efficiency (PCE) of 25.3% and retain almost 90% of the initial values after aging at 85°C for 1500 hours in N2. More encouragingly, the solution-processed BTPC60 ETL demonstrates remarkable film thickness tolerance, and enables a high PCE up to 24.8% with the ETL thickness of 200 nm. Our results highlight BTPC60 as a promising solution-processed fullerene-based ETM, opening an avenue for improving the scalability of efficient and stable inverted PSCs.

The Promise and Challenges of Inverted Perovskite Solar Cells.

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Target therapy on buried interface engineering enables stable inverted perovskite solar cells with 25 % power conversion efficiency

buried interfaces are crucial for achieving efficient and stable perovskite solar cells (PSCs). However, studying and optimizing buried interfaces remains a challenging issue due to its non-exposed characteristics. Here, a simple and effective targeting strategy is proposed to regulate the NiOx/perovskite buried interface by passivating buried defects in perovskite and adjusting the growth of perovskite crystals through modifying multifunctional molecules (DTD) on the surface of NiOx. DTD has multifunctional targeting groups that enable it to interact strongly with both perovskite and NiOx simultaneously, thereby building a molecular bridge at the NiOx/perovskite buried interface, enabling high-quality upper perovskite films, excellent interface contact and more matched energy levels between perovskite and NiOx. As a result, the modification of DTD significantly improves the efficiency of perovskite devices from 22.19 % to 25.00 % (certified value of 24.12 %), along with excellent long-term and operational stability. This strategy provides a simple and effective targeted therapy for the buried interface in PSC, achieving high efficiency and stability.

Cyclic Multi‐Site Chelation for Efficient and Stable Inverted Perovskite Solar Cells

Trap‐assisted non‐radiative recombination losses and moisture‐induced degradation significantly impede the development of highly efficient and stable inverted (p‐i‐n) perovskite solar cells (PSCs), which require high‐quality perovskite bulk. In this research, we mitigate these challenges by integrating thermally stable perovskite layers with Lewis base covalent organic frameworks (COFs). The ordered pore structure and surface binding groups of COFs facilitate cyclic, multi‐site chelation with undercoordinated lead ions, enhancing the perovskite quality across both its bulk and grain boundaries. This process not only reduces defects but also promotes improved energy alignment through n‐type doping at the surface. The inclusion of COF dopants in p‐i‐n devices achieves power conversion efficiencies (PCEs) of 25.64% (certified 24.94%) for a 0.0748‐cm2 device and 23.49% for a 1‐cm2 device. Remarkably, these devices retain 81% of their initial PCE after 978 hours of accelerated aging at 85˚C, demonstrating remarkable durability. Additionally, COF‐doped devices demonstrate excellent stability under illumination and in moist conditions, even without encapsulation.

Efficient and Stable Inverted Perovskite Solar Cells Enabled by a Fullerene-Based Hole Transport Molecule.

Designing an efficient modification molecule to mitigate non-radiative recombination at the NiOx/perovskite interface and improve perovskite quality represents a challenging yet crucial endeavor for achieving high-performance inverted perovskite solar cells (PSCs). Herein, we synthesized a novel fullerene-based hole transport molecule, designated as FHTM, by integrating C60 with 12 carbazole-based moieties, and applied it as a modification molecule at the NiOx/perovskite interface. The in-situ self-doping effect, triggered by electron transfer between carbazole-based moiety and C60 within the FHTM molecule, along with the extended π conjugated moiety of carbazole groups, significantly enhances FHTM's hole mobility. Coupled with optimized energy level alignment and enhanced interface interactions, the FHTM significantly enhances hole extraction and transport in corresponding devices. Additionally, the introduced FHTM efficiently promotes homogeneous nucleation of perovskite, resulting in high-quality perovskite films. These combined improvements led to the FHTM-based PSCs yielding a champion efficiency of 25.58% (Certified: 25.04%), notably surpassing that of the control device (20.91%). Furthermore, the unencapsulated device maintained 93% of its initial efficiency after 1000 hours of maximum power point tracking under continuous one-sun illumination. This study highlights the potential of functionalized fullerenes as hole transport materials, opening up new avenues for their application in the field of PSCs.

Dimensional Engineering in Efficient and Stable Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have attracted much attention in the field of photovoltaics, due to their high power conversion efficiency (PCE) and low cost. In recent years, inverted PSCs have achieved significant advancements in PCE and operational stability. Among the strategies for optimizing PCE and lifespan of inverted PSCs, dimensional engineering plays a critical role and garners increasing attention due to its versatile functions of passivating defects, releasing residual tensile stress, strengthening structural stability, ameliorating carrier transport and extraction, and so on. Considering the importance of dimensional engineering, a comprehensive and deep understanding of 2D perovskites and 2D/3D heterojunction is definitely necessary. In this review, first, the progress of low‐dimensional perovskite light‐harvesting materials in inverted PSCs is summarized. Subsequently, the advances in constructing 2D/3D perovskite heterojunctions, including 2D/3D bulk heterojunction within perovskite materials, 2D/3D interfacial heterojunction at the interface between perovskite film and carrier transport layer, and bottom‐up 2D/3D perovskite heterojunction are discussed. The simultaneous construction of 2D/3D heterojunction at dual interfaces is highlighted. Finally, the legitimate outlook on the further development of dimensional engineering is proposed to advance the commercialization of inverted photovoltaic technology.

Surface passivation enables efficient and stable inverted perovskite solar cells by 6-(Trifluoromethyl)pyridine-3-amidinehydrochloride

The inverted p-i-n PSCs are gradually gaining more attention since they are generally more stable and can employ low-cost transport materials. However, the interfaces between the perovskite and the charge transport layers contribute to major power conversion efficiency (PCE) loss and instability. Here, we use a material of 6-(Trifluoromethyl)pyridine-3-amidinehydrochloride (CF3-PyFACl) to molecularly engineer the interface between the perovskite and electron transport layer. The interface modification results in suppressed nonradiative recombination, and improved interfacial contact. A PCE of 23.17 % is demonstrated, with open-circuit voltage (Voc) and fill factor (FF) of 1.169 V and 84.1 %, respectively. The unencapsulated device retains >80 % of the initial performance after 400 h continuous light soaking.

Effective surface treatment for efficient and stable inverted inorganic CsPbI2Br perovskite solar cells

The interest in all-inorganic perovskite solar cells (PSCs) featuring a p-i-n structure is on the rise, attributed to their superior heat resistance and adaptability with tandem cell methods. However, their progress has been far from the regular structure owing to the comparatively low open circuit voltage (Voc). This research employs phenylethylammonium iodide, incorporating various side groups, as passivators to tackle the previously mentioned problems and investigate their effects on passivation. It is found that a reduction of trap-state density in perovskite film was accomplished due to the PEAI effective passivation effect by establishing coordination with the under-coordinated Pb2+ ions. Furthermore, there was an enhancement in the alignment of energy levels at the CsPbI2Br perovskite/PCBM junction, resulting in better charge extraction from the CsPbI2Br layer to the charge transport layer. As a result, an improved champion efficiency of 14.26 % with a Voc of 1.11 V, Jsc of 16.21 mA/cm2, and FF of 79.28 % was yielded for the PEAI treatment inverted CsPbI2Br device, compared with the 12.15 % efficiency of the control device. Superior device stability was exhibited for the optimal PEAI-treated devices without encapsulation. This research validates the significance of a side group on a surface passivation molecule to effectively passivate defects and optimize energy levels, especially for boosting Voc.

Glycol Monomethyl Ether-Substituted Carbazolyl Hole-Transporting Material for Stable Inverted Perovskite Solar Cells with Efficiency of 25.52 .

Organic self-assembled molecules (OSAMs) based hole-transporting materials play a pivotal role in achieving highly efficient and stable inverted perovskite solar cells (IPSCs). However, the reported carbazol-based OSAMs have serious drawbacks, such as poor wettability for perovskite solution spreading due to the nonpolar surface, worse matched energy arrangement with perovskite, and limited molecular species, which greatly limit the device performance. To address above problems, a novel OSAM [4-(3,6-glycol monomethyl ether-9H-carbazol-9-yl) butyl]phosphonic acid (GM-4PACz) was synthesized as hole-transporting material by introducing glycol monomethyl ether (GM) side chains at carbazolyl unit. GM groups enhance the surface energy of Indium Tin Oxide (ITO)/SAM substrate to facilitate the nucleation and growth of up perovskite film, suppress cation defects, release the residual stress at SAM/perovskite interface, and evaluate energy level for matching with perovskite. Consequently, the GM-4PACz based IPSC achieves a champion PCE of 25.52 %, a respectable open-circuit voltage (VOC) of 1.21 V, a high stability, possessing 93.29 % and 91.75 % of their initial efficiency after aging in air for 2000 h or tracking at maximum power point for 1000 h, respectively.