Inverted Perovskite Solar Cells Research Articles

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.

Tailored Polymer Hole-Transporting Materials with Multisite Passivation Functions for Effective Buried-Interface Engineering of Inverted Quasi-2D Perovskite Solar Cells.

Although quasi-2D Ruddlesden‒Popper (RP) perovskite exhibits advantages in stability, their photovoltaic performance are still inferior to 3D counterparts. Optimizing the buried interface of RP perovskite and suppress energetic losses can be a promising approach for enhancing efficiency and stability of inverted quasi-2D RP perovskite solar cells (PSCs). Among which, constructing polymer hole-transporting materials (HTMs) with defect passivation functions is of great significance for buried-interface engineering of inverted quasi-2D RP PSCs. Herein, by employing side-chain tailoring strategy to extend the π-conjugation and regulate functionality of side-chain groups, target polymer HTMs (PVCz-ThSMeTPA and PVCz-ThOMeTPA) with high mobility and multisite passivation functions are achieved. The presence of more sulfur atom-containing groups in side-chain endows PVCz-ThSMeTPA with increased intra/intermolecular interaction, appropriate energy level, and enhanced buried interfacial interactions with quasi-2D RP perovskite. The hole mobility of PVCz-ThSMeTPA is up to 9.20×10-4 cm2 V-1 S-1. Furthermore, PVCz-ThSMeTPA as multifunctional polymer HTM with multiple chemical anchor sites for buried-interface engineering of quasi-2D PSCs can enable effective charge extraction, defects passivation, and perovskite crystallization modulation. Eventually, the PVCz-ThSMeTPA-based inverted quasi-2D PSC achieves a champion power conversion efficiency of 22.37%, which represents one of the highest power conversion efficiencies reported to date for quasi-2D RP PSCs.

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.

Sustainable Molecular Passivation via Heat-Induced Disaggregation and Redox Reactions for Inverted Perovskite Solar Cells

Sustainable Molecular Passivation via Heat-Induced Disaggregation and Redox Reactions for Inverted Perovskite Solar Cells

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.

Humidity Resistance of Inverted Perovskite Solar Cells as Measured by Operando X-ray Scattering

Humidity Resistance of Inverted Perovskite Solar Cells as Measured by Operando X-ray Scattering

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

One‐Stone‐For‐Three‐Birds Strategy Using a Fullerene Modifier for Efficient and Stable Inverted Perovskite Solar Cells

AbstractThe electron extraction from perovskite/C60 interface plays a crucial role in influencing the photovoltaic performance of inverted perovskite solar cells (PSCs). Here, we develop a one‐stone‐for‐three‐birds strategy via employing a novel fullerene derivative bearing triple methyl acrylate groups (denoted as C60‐TMA) as a multifunctional interfacial layer to optimize electron extraction at the perovskite/C60 interface. It is found that the C60‐TMA not only passivates surface defects of perovskite via coordination interactions between C=O groups and Pb2+ cations but also bridge electron transfer between perovskite and C60. Moreover, it effectively induces the secondary grain growth of the perovskite film through strong bonding effect, and this phenomenon has never been observed in prior art reports on fullerene related studies. The combination of the above three upgrades enables improved perovskite film quality with increased grain size and enhanced crystallinity. With these advantages, C60‐TMA treated PSC devices exhibit a much higher power conversion efficiency (PCE) of 24.89 % than the control devices (23.66 %). Besides, C60‐TMA benefits improved thermal stability of PSC devices, retaining over 90 % of its initial efficiency after aging at 85 °C for 1200 h, primarily due to the reinforced interfacial interactions and improved perovskite film quality.

One-Stone-For-Three-Birds Strategy Using a Fullerene Modifier for Efficient and Stable Inverted Perovskite Solar Cells.

The electron extraction from perovskite/C60 interface plays a crucial role in influencing the photovoltaic performance of inverted perovskite solar cells (PSCs). Here, we develop a one-stone-for-three-birds strategy via employing a novel fullerene derivative bearing triple methyl acrylate groups (denoted as C60-TMA) as a multifunctional interfacial layer to optimize electron extraction at the perovskite/C60 interface. It is found that the C60-TMA not only passivates surface defects of perovskite via coordination interactions between C=O groups and Pb2+ cations but also bridge electron transfer between perovskite and C60. Moreover, it effectively induces the secondary grain growth of the perovskite film through strong bonding effect, and this phenomenon has never been observed in prior art reports on fullerene related studies. The combination of the above three upgrades enables improved perovskite film quality with increased grain size and enhanced crystallinity. With these advantages, C60-TMA treated PSC devices exhibit a much higher power conversion efficiency (PCE) of 24.89 % than the control devices (23.66 %). Besides, C60-TMA benefits improved thermal stability of PSC devices, retaining over 90 % of its initial efficiency after aging at 85 °C for 1200 h, primarily due to the reinforced interfacial interactions and improved perovskite film quality.

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.

Reducing Interfacial Recombination in Inverted Perovskite Solar Cells With Selenophene-Substituted PCBM: Comparison With Thiophene and Furan Substitution.

Reducing the interfacial recombination and improving the charge transfer capability of charge transport layers are effective strategies to enhance the efficiency and stability of perovskite solar cells (PSCs). This study evaluates, for the first time, the effects of selenophene substitution in the chemical structure of phenyl-butyric acid methyl ester (PCBM) on the performance and stability of inverted PSCs. Selenophene substitution was compared to thiophene and furan substitutions, and the reference PCBM without chalcogenophene moiety. Additionally, this study investigates the differences between using the fullerene cages C70 and C60 in the PCBM chemical structure. The photovoltaic results demonstrate that, with an adequate control of the thickness of the electron transport layer (ETL), incorporating the selenophene moiety in the structures of fullerenes enhances the photovoltaic parameters of PSCs. This improvement results from the reduction in trap-assisted recombination, an increase in electron mobility, and the improved charge extraction processes. The use of C70, as opposed to C60, allows for the preparation of a series of ETLs with comparable thicknesses, although slightly lower efficiencies. This feature facilitates a systematic comparative analysis focused on variations in the electron properties of ETLs, thereby avoiding the inclusion of issues related to thickness and charge recombination processes.

Indolo[3,2-b]carbazole-Based Self-Assembled Monolayer Enables High-Performance Inverted Perovskite Solar Cells with Over 25.5% Efficiency

Indolo[3,2-b]carbazole-Based Self-Assembled Monolayer Enables High-Performance Inverted Perovskite Solar Cells with Over 25.5% Efficiency

Enhanced Corrosion Resistance of Ag Electrode Through Ionized 2‐Mercaptobenzothiazole in Inverted Perovskite Solar Cells

AbstractThe utilization of Ag electrodes in inverted perovskite solar cells (PSCs) is prevalent; however, their inherent reactivity and corrosive characteristics toward perovskite materials often lead to significant stability concerns. Here, 1‐ethyl‐3‐methyl‐1h‐imidazolium 2‐mercaptobenzothiazole (EM) ionic liquid is designed and introduce it into the bathocuproine (BCP) barrier layer to mitigate the potential chemical corrosion of the Ag electrode by the perovskite layer. EM forms multiple interaction modes through the coordination of two types of bonds, C─N, C═N, and C─S, and chelation with Ag, resulting in the formation of a dense chemical anti‐corrosion layer on the Ag surface. By raising the Ag electrode's corrosion potential and decreasing its corrosion current, the occurrence of chemical reactions and corrosion of the Ag electrode by the perovskite layer is effectively suppressed. Additionally, the ionized EM optimizes the band structure and conductivity of BCP and enhances the electron transfer capability at the electron transport layer/Ag interface. The BCP:EM‐based inverted PSCs exhibit an efficiency of 25.11% and excellent stability. Under continuous operation at 45 °C and one sun illumination, the encapsulated device maintains 85.6% of its initial efficiency after 1000 h at the maximum power point.

LiF in Inverted Perovskite Solar Cells: Dipole or Doping?

LiF in Inverted Perovskite Solar Cells: Dipole or Doping?

Organic Salt Buffer Layer Enables High‐Performance NiOx‐Based Inverted Perovskite Solar Cells

The merits of a low‐cost fabrication process, suitable band structure, excellent wettability to perovskite precursor, and outstanding stability ensure NiOx as a hole transport material with beneficial characteristics to construct high‐performance perovskite solar cells (PSCs). However, direct contact between perovskite and NiOx causes delamination and chemical instability and thus results in poor carrier transport and short device lifespan. Here, we propose a solution for this issue by introducing an organic salt additive 4‐(trifluoromethyl) benzylammonium formate (TFMBAFa) in the perovskite precursor to passivate perovskite film and NiOx@(2‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) ethyl) phosphonic acid (Me‐2PACz) composited hole transport layer (HTL), and thus construct a buffer layer between perovskite‐HTL interface. The effective diminishing of NiOx/perovskite interfacial reactions and defects results in enhanced carrier transport. Consequently, the target device achieves simultaneous improvements in power conversion efficiency (24.2%), storage stability (T100 > 1400 h), thermal stability (T80 > 1000 h), and operational stability (T70 > 850 h), where T100, T80, and T70 refer to the retention of 100%, 80%, and 70% of initial PCE, respectively. This work provides an effective strategy to advance the performance of NiOx‐based inverted PSCs.

Asymmetric Modification of Carbazole Based Self-Assembled Monolayers by Hybrid Strategy for Inverted Perovskite Solar Cells.

Carbazole-based self-assembled molecules (SAMs) are widely applied in inverted perovskite solar cells (iPSCs) due to their unique molecular properties. However, the symmetrical structure of the carbazole-based SAMs makes it difficult to finely regulate their performance, which impedes the further enhancement of the efficiency and stability of iPSCs. This work shows that by building an asymmetric carbazole core, the crucial properties of SAM molecules can be effectively regulated. It has been confirmed that the hybrid thieno[2,3-b]thiophene unit of this asymmetric core governs the energy level, the surface wettability, and the defect passivation capability of the SAMs, while the substituent of core has a greater impact on the molecular dipole and device stability. The synergistic effects from thieno[2,3-b]thiophene and fluorine lead to the KF-derived iPSC demonstrating a certified power conversion efficiency (PCE) of 25.17% and excellent operational stability. This hybrid design concept offers a promising approach for the further structural modification of SAMs in iPSCs.

Asymmetric Modification of Carbazole Based Self‐Assembled Monolayers by Hybrid Strategy for Inverted Perovskite Solar Cells

Asymmetric Modification of Carbazole Based Self‐Assembled Monolayers by Hybrid Strategy for Inverted Perovskite Solar Cells

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%.