Interface In Solar Cells Research Articles

Crystallization Regulation by Self-Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells.

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.

Halide Substituted Ammonium Salt Optimized Buried Interface for Efficient and Stable Flexible Perovskite Solar Cells

AbstractLow‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, the performance of flexible perovskite solar cells (f‐PSCs) lags far behind their rigid counterpart in terms of efficiency and stability. Emerging evidence demonstrates that the quality of the buried interface between perovskite and transporting layer underneath is the key point. Herein, a class of novel halide substituted ammonium salts, i.e., n‐bromophenethylammonium (n‐Br‐PEAX, n = 2 or 4, X = Cl or Br) are designed and synthesized to modify the buried interface as well as the perovskite crystallization of f‐PSCs. It is found that the ammonium salt with rational design molecular structure can modify the crystallization speed of perovskite, leading to the formation of a compact and uniform morphology without nanovoids at the interface. As a result, the efficiency of f‐PSCs is improved from 15.4% to 20.2%. Moreover, the modified devices without encapsulation retain 86% of their initial performance after 1000 h of aging at ambient conditions and 87% after 290 h of continuous operation.

Methoxy‐Based Passivator 4‐Methoxyphenethylammonium Iodide as Multifunctional Passivator for High‐Efficiency 3D/2D Flexible Perovskite Solar Cells over 23%

As is well known, the interface of perovskite solar cells (PSCs) is rich in deep‐level carrier traps, which act as non‐radiative recombination centers and limit the open‐circuit voltage (VOC) and power conversion efficiency (PCE) of PSCs. Defect chemistry and surface passivation agents have been extensively studied, primarily focusing on the neutralization of non‐coordinated lead or anion defects. Herein, a novel methoxy‐based passivator 4‐methoxyphenethylammonium iodide (p‐MeOPEAI) is introduced for a multifunctional passivation effect at the perovskite interface. It is susceptible for p‐MeOPEAI to form 2D perovskite on top of 3D perovskite, and it interacts with the surface of 3D perovskite in multiple ways, forming a 3D/2D structure that facilitates charge transfer and p‐MeOPEAI passivates the uncoordinated Pb2+ ions of the perovskite film surface. The interface defects in the PSCs are well passivated, minimizing non‐radiative recombination and enhancing device performance. As a result, a champion PCE of 23.3% is achieved for flexible PSCs with a high VOC (1.2 V). In addition, modified devices also show enhanced operational mechanical stability (retention of >80% initial PCE after 10 000 bending cycles).

Influence of thiourea concentration during deposition of a CdS buffer layer on the electric properties of Cu2SnS3 solar cells

The p–n interface state and depletion layer region of solar cells were investigated using electrochemical impedance spectroscopy (EIS) measurements to elucidate the effect of varying thiourea (TU) concentrations in chemical bath deposition (CBD) on the photovoltaic properties of Cu2SnS3 (CTS) solar cells. The photoconversion efficiency (PCE) increased as the TU concentration increased, peaking at 0.16 M and decreasing thereafter. Additionally, the constant phase element-p value, which is indicative of the p–n interface state in CTS solar cells, exhibited a similar trend to that of the PCE of CTS solar cells with increasing TU concentration. The decrease in the PCE was due to the electron recombination that occurred at the p–n interface of CTS solar cells with increasing TU concentrations. Therefore, to improve the PCE of the CTS solar cells, the TU concentration in CBD must be optimized because the p–n interface state is sensitive to changes in the growth conditions of CdS films. By studying the effects on the p–n interface state and depletion layer in CTS solar cells using EIS measurements, useful knowledge can be obtained to increase the PCE of all-sulfide-compound solar cells using n-type CdS films as well as CTS.

Formamidine formate as the multifunctional modulator at buried interface for efficient FAPbI3 perovskite solar cells

Interface modification is recognized as an effective strategy to promote the performance of perovskite solar cells (PSCs) especially after the thorough optimization on film fabrication process. Device performance is augmented considerably by passivating the perovskite surface utilizing variety of materials. On the other hand, buried interface revealed a higher defect density than top surface, hence, rational optimization of buried interface is getting paramount for the further amelioration on efficiency and stability of PSCs. Herein, formamidine formate (FAFa) with both carboxyl and amino groups is employed to modify the buried interface between SnO2 and perovskite. It is demonstrated that FAFa treatment can enhance the electrical properties of SnO2 and optimize the band alignment. Meanwhile, it improves the contact performance by constructing a chemical bridge at the buried interface. Moreover, it endows high quality perovskite by modulating the growth process. Consequently, the power conversion efficiency of FAPbI3 PSCs is elevated substantially from 20.89% to 23.11% mainly benefitted from the suppressed carrier recombination and facilitated electron extraction at the buried interface. Meanwhile, corresponding device illustrated reinforced durability both in inert and atmospheric environment. Our work presented a convenient way to modify the buried interface for the further enhancement of PSC performance.

Anchoring self-assembled monolayer at perovskite/hole collector interface for wide bandgap Sn-based solar cells with a record efficiency over 12%

In perovskite solar cells (PSCs), surface and interfacial conditions play a crucial role in determining overall device performance. In typical p-i-n architecture of wide bandgap (WBG, 1.6–1.8 eV) Sn-based PSCs, the interface between hole transport layer (HTL) and perovskite (PVK) has a significant impact on hole transport, interfacial chemical interactions, and perovskite film quality. This study aims to address these issues by incorporating self-assembled monolayers (SAMs) MeO-2PACz and 2PACz at the PEDOT:PSS HTL/Sn-PVK interface. X-ray photoelectron spectroscopy confirmed the interaction between the anchoring group (P-O−) of the SAM and S+ in PEDOT:PSS through phosphonic acid deprotonation at the interface, and improved work function was observed through the UPS study. Furthermore, the SAMs contributed to the formation of a compact PVK film with enhanced preferential orientation. Interestingly, a chemical interaction between the oxygen-donor of the methoxy (CH3O−) terminal group in MeO-2PACz and the Sn-halide octahedra was observed, which partly contributed to suppress the oxidation of Sn2+ state and defect density of perovskite. Additionally, femtosecond transient absorption spectroscopy (fs-TAS) showed faster trap filling (τ1) characteristics (τ1∼19 ps). Fs-TAS and photoluminescence further indicated fast hole extraction (τ2∼125 ps) as well as high quenching efficiency of 47%. Based on these findings, an unprecedented efficiency of η∼12.16% (certified 11.60%) was achieved in WBG Sn-PSCs using the HTL/MeO-2PACz/PVK structure, outperforming the HTL/2PACz/PVK (8.78%) and HTL/PVK (7.44%) structures. This study provides crucial guidelines on interfacial engineering for WBG Sn-PSCs.

Carrier Modulation via Tunnel Oxide Passivating at Buried Perovskite Interface for Stable Carbon-Based Solar Cells.

Carbon-based perovskite solar cells (C-PSCs) have the impressive characteristics of good stability and potential commercialization. The insulating layers play crucial roles in charge modulation at the buried perovskite interface in mesoporous C-PSCs. In this work, the effects of three different tunnel oxide layers on the performance of air-processed C-PSCs are scrutinized to unveil the passivating quality. Devices with ZrO2-passivated TiO2 electron contacts exhibit higher power conversion efficiencies (PCEs) than their Al2O3 and SiO2 counterparts. The porous feature and robust chemical properties of ZrO2 ensure the high quality of the perovskite absorber, thus ensuring the high repeatability of our devices. An efficiency level of 14.96% puts our device among the state-of-the-art hole-conductor-free C-PSCs, and our unencapsulated device maintains 88.9% of its initial performance after 11,520 h (480 days) of ambient storage. These results demonstrate that the function of tunnel oxides at the perovskite/electron contact interface is important to manipulate the charge transfer dynamics that critically affect the performance and stability of C-PSCs.

Bidirectional passivation of the SnO2/perovskite interface in perovskite solar cells through organic salt 3-Hydroxytyramine hydrochloride

SnO2 offers compelling advantages as an excellent electron transport layer material in perovskite solar cells. However, the defects caused by oxygen vacancies are unfavorable to the interface contact and would hinder the device performance. A simple and effective interface passivation strategy using 3-Hydroxytyramine hydrochloride (3-Hh) is developed, which realizes the bidirectional passivation of electron transport layer and perovskite. The passivation mechanism of 3-Hh is investigated. Further, the morphology of the subsequent deposited perovskite film is improved. The modified perovskite film exhibits increased grain size with better uniformity, reduced grain boundaries, lowered defect density. A relatively higher power conversion efficiency of 22.63% is achieved for the perovskite solar cells based on the bidirectional passivation of SnO2/perovskite interface. Meanwhile, the modified devices can retain 80% and 82% of the initial efficiency after storage for 1400 ​h in air and 700 ​h in 85 ​°C, respectively. The results show that 3-Hh could be a promising multifunctional interface material to further enhance the efficiency and the stability of perovskite solar cells.

Understanding Contact Nonuniformities at Interfaces in Perovskite Silicon Tandem Solar Cells Using Luminescence Imaging, Lock‐In Thermography, and 2D/3D Simulations

The top cell of a perovskite silicon tandem solar cell requires several material layers on each side of the perovskite absorber to efficiently extract electrons and holes, respectively. These layers must meet multiple requirements simultaneously, namely, low interface recombination, good charge carrier selectivity, low contact resistivity, and high optical transparency. Due to the complex architecture, characterization techniques are required in material and process optimization to identify loss mechanisms. Spatial resolution of the characterization is gaining importance along with the upscaling of the perovskite technology. Herein, electro‐ and photoluminescence (EL and PL) imaging is combined with illuminated lock‐in thermography (ILIT) for a comprehensive electro‐optical characterization of both subcells in perovskite silicon tandem devices with state‐of‐the‐art cell architecture. Thereby, the combination of the presented characterization methods together with numerical simulation models enables to carry out holistic investigations of device limitations. The strength of this approach is showcased by one particularly remarkable feature that is observed in the investigated tandem device, showing a low PL but high EL signal at local spots. Together with multidimensional optoelectrical device simulations, the measurements are explained and the root cause of this feature to originate from the perovskite/C60 interface is suggested.

Regulating Orientational Crystallization and Buried Interface for Efficient Perovskite Solar Cells Enabled by a Multi‐Fluorine‐Containing Higher Fullerene Derivative

AbstractPerovskite films prepared by the solution process usually result in irregular grain orientation and rich buried interface defects, hindering the further improvement of device performance. Herein, multi‐fluorine‐containing C60‐ and C70 (higher fullerene)‐porphyrin derivatives, F60PD and F70PD, are synthesized and pre‐buried to modify the SnO2/perovskite heterointerface. The F70PD modification layer provides a better perovskite quality and more effective electron transporting capability compared to the corresponding F60PD, with the F70PD being more effective in regulating the perovskite growth, passivating the buried interface defects, and optimizing the interface energy level alignment. Consequently, the F70PD‐based device delivers superior efficiency and stability than the control and F60PD‐based devices. The F70PD‐based device yields a champion efficiency of 24.09% with negligible hysteresis. Meanwhile, due to the increased activation energy of ion migration, the F70PD‐based device maintains 80% of its initial efficiency after operating at the maximum power point for 1620 h. This study highlights the potential of designing higher fullerene materials for buried interface to further improve the perovskite solar cells’ performance.

Chemical and Electronic Properties of PTB7-Th and ITIC on ZnO Interfaces in Organic Solar Cells

Chemical and Electronic Properties of PTB7-Th and ITIC on ZnO Interfaces in Organic Solar Cells

Differently shaped Ag crystallites and four current transport paths at sintered Ag/Si interface of crystalline silicon solar cells

The comprehensive understanding of the Ohmic contact mechanism on the front metalization is highly desirable for further improvement of crystalline silicon solar cells performance. However, there are still controversial views about current transport paths between silver electrode and silicon emitter. To clarify this significant issue, we applied the selective acid etching (AE) process and the method of mechanical stripping process to prepare proper samples for direct observation of the Ag/Si contact interface. It is revealed that four kinds of Ag crystallites are grown with variant shapes and sizes on the pyramid tips, {111} planes, edges and tiny bumps at valleys of the textured Si surface resulting from anisotropic etching of Si emitter by the flowing molten glass frit during firing and the consequent epitaxially growth of Ag on the etching pits during cooling. All these Ag crystallites are in direct contact with Si emitter, serving as the most important contact points on the Si side. Meanwhile, three kinds of spherical Ag particles are formed in the resolidified glass frit during cooling which are crucial tunneling paths, conducting between glass-covered Ag crystallites on silicon and Ag bulk above. As a whole, four current transport paths are suggested mainly via Ag crystallites, Ag particles or both. In addition, the four electron transport paths are further confirmed by the Kelvin probe force microscopy characterization. The clarification and detailed understanding of all current transport paths are key points to design better silver paste and sintering process, and hence to improve the solar cell performance.

Target Therapy for Buried Interface Enables Stable Perovskite Solar Cells with 25.05% Efficiency.

The buried interface in perovskite solar cells (PSCs) is pivotal for achieving high efficiency and stability. However, it is challenging to study and optimize the buried interface due to its non-exposed feature. Here, a facile and effective strategy is developed to modify the SnO2 /perovskite buried interface by passivating the buried defects in perovskite and modulating carrier dynamics via incorporating formamidine oxalate (FOA) in SnO2 nanoparticles. Both formamidinium and oxalate ions show a longitudinal gradient distribution in the SnO2 layer, mainly accumulating at the SnO2 /perovskite buried interface, which enables high-quality upper perovskite films, minimized defects, superior interface contacts, and matched energy levels between perovskite and SnO2 . Significantly, FOA can simultaneously reduce the oxygen vacancies and tin interstitial defects on the SnO2 surface and the FA+ /Pb2+ associated defects at the perovskite buried interface. Consequently, the FOA treatment significantly improves the efficiency of the PSCs from 22.40% to 25.05% and their storage- and photo-stability. This method provides an effective target therapy of buried interface in PSCs to achieve very high efficiency and stability.

Molecular Bridge on Buried Interface for Efficient and Stable Perovskite Solar Cells.

The interface of perovskite solar cells (PSCs) is significantly important for charge transfer and device stability, while the buried interface with the impact on perovskite film growth has been paid less attention. Herein, we use a molecular modifier, glycocyamine (GDA) to build a molecular bridge on the buried interface of SnO2 /perovskite, resulting in superior interfacial contact. This is achieved through the strongly interaction between GDA and SnO2 , which also appreciably modulates the energy level. Moreover, GDA can regulate the perovskite crystal growth, yielding perovskite film with enlarged grain size and absence of pinholes, exhibiting substantially reduced defect density. Consequently, PSCs with GDA modification demonstrate significant improvement of open circuit voltage (close to 1.2 V) and fill factor, leading to an improved power conversion efficiency from 22.60 % to 24.70 %. Additionally, stabilities of GDA devices under maximum power point and 85 °C heat both perform better than the control devices.

Molecular Bridge on Buried Interface for Efficient and Stable Perovskite Solar Cells

AbstractThe interface of perovskite solar cells (PSCs) is significantly important for charge transfer and device stability, while the buried interface with the impact on perovskite film growth has been paid less attention. Herein, we use a molecular modifier, glycocyamine (GDA) to build a molecular bridge on the buried interface of SnO2/perovskite, resulting in superior interfacial contact. This is achieved through the strongly interaction between GDA and SnO2, which also appreciably modulates the energy level. Moreover, GDA can regulate the perovskite crystal growth, yielding perovskite film with enlarged grain size and absence of pinholes, exhibiting substantially reduced defect density. Consequently, PSCs with GDA modification demonstrate significant improvement of open circuit voltage (close to 1.2 V) and fill factor, leading to an improved power conversion efficiency from 22.60 % to 24.70 %. Additionally, stabilities of GDA devices under maximum power point and 85 °C heat both perform better than the control devices.

Suppressing Excess Lead Iodide Aggregation and Reducing N-Type Doping at Perovskite/HTL Interface for Efficient Perovskite Solar Cells.

Excess lead iodide (PbI2 ) aggregation at the charge carrier transport interface leads to energy loss and acts as unstable origins in perovskite solar cells (PSCs). Here, a strategy is reported to modulate the interfacial excess PbI2 by introducing π-conjugated small-molecule semiconductors 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC) into perovskite films through an antisolvent addition method. The coordination of TAPC to PbI units through the electron-donating triphenylamine groups and π-Pb2+ interactions allows for a compact perovskite film with reduced excess PbI2 aggregates. Besides, preferred energy level alignment is achieved due to the suppressed n-type doping effect at the hole transport layer (HTL) interfaces. As a result, the TAPC-modified PSC based on Cs0.05 (FA0.85 MA0.15 )0.95 Pb(I0.85 Br0.15 )3 triple-cation perovskite achieved an improved PCE from 18.37% to 20.68% and retained ≈90% of the initial efficiency after 30 days of aging under ambient conditions. Moreover, the TAPC-modified device based on FA0.95 MA0.05 PbI2.85 Br0.15 perovskite produced an improved efficiency of 23.15% compared to the control (21.19%). These results provide an effective strategy for improving the performance of PbI2 -rich PSCs.

Phenanthroline-carbolong interface suppress chemical interactions with active layer enabling long-time stable organic solar cells

To restrain the chemical reaction at cathode interface of organic solar cells, two cathode interfacial materials are synthesized by connecting phenanthroline with carbolong unit. Consequently, the D18:L8-BO based organic solar cell with double-phenanthroline-carbolong achieve the highest efficiency of 18.2%. Double-phenanthroline-carbolong with larger steric hindrance and stronger electron-withdrawing property confirms to suppress the interfacial reaction with norfullerene acceptor, resulting the most stable device. Double-phenanthroline-carbolong based device can sustain 80% of its initial efficiency for 2170 h in dark N2 atmosphere, 96 h under 85 oC and keep 68% initial efficiency after been illuminated for 2200 h, which are significantly better than bathocuproin based devices. Moreover, superb interfacial stability of double-phenanthroline-carbolong cathode interface enables thermal posttreatment of organic sub-cell in perovskite/organic tandem solar cells and obtained a remarkable efficiency of 21.7% with excellent thermal stability, which indicates the potentially wide application of phenanthroline-carbolong materials for stable and efficient solar device fabrications.

Synergistic effects of caesium closo-dodecaborate on buried interface for efficient and stable perovskite solar cells

The defects and strain of the buried SnO2/perovskite interface seriously affects the performances of n-i-p type perovskite solar cells. Herein, caesium closo-dodecaborate (B12H12Cs2) is introduced into buried interface to improve the device performances. B12H12Cs2 can passivate the bilateral defects of the buried interface, including the oxygen vacancy and uncoordinated Sn2+ defects on SnO2 side and the uncoordinated Pb2+ defects on perovskite side. Three-dimensional aromatic B12H12Cs2 can promote the interface charge transfer and extraction. [B12H12]2− can enhance the interface connection of buried interface by forming B-H---H-N dihydrogen bond and coordination bonds with metal ions. Meanwhile, the crystal properties of perovskite films can be improved and the buried tensile strain can be released by B12H12Cs2 due to the matched lattice between B12H12Cs2 and perovskite. In addition, Cs+ can diffuse into perovskite to reduce the hysteresis behavior by inhibiting the I− migration. Arising from the enhanced connection performances, passivated defects, improved perovskite crystallization, enhanced charge extraction, inhibited ions migration, released tensile strain at buried interface by B12H12Cs2, the corresponding devices yield a champion power conversion efficiency of 22.10% with enhanced stability. The stability of devices by B12H12Cs2 modification have been improved, and it can still maintain 72.5% of the original efficiency after 1440 h, while the control devices can only maintain 20% of the original efficiency after aging in air condition of 20–30% RH.

Optimization of a Molybdenum Oxide Bilayer Facilitating Hole Transfer in the p/i Interface for Transparent Thin-Film Silicon Solar Cells and Modules Using Laser Scribing

Optimization of a Molybdenum Oxide Bilayer Facilitating Hole Transfer in the p/i Interface for Transparent Thin-Film Silicon Solar Cells and Modules Using Laser Scribing

Improving the charge carrier separation efficiency at the perovskite/carbon electrode interface in HTL-free carbon-based perovskite solar cells via physical polishing

Carbon-based perovskite solar cells (C-PSCs) are favored by researchers for their low cost and support for large-scale production. However, the particles precipitated on the surface of the perovskite (PVK) film can affect the fabrication and operation of C-PSC, such as disrupting the coating of C electrode film and producing defects that can aggravate the carrier recombination. Herein a reliable and efficient C-PSC is prepared by applying a physical polishing strategy. The compact interface contact and the larger Fermi level difference at the carbon-PVK (C/PVK) interface are achieved, resulting in a 21.4% increase in power conversion efficiency compared to that without polishing. A hole-transport-layer-free C-PSC with an efficiency of 12.2% is achieved, resulting from the reduction of PVK surface roughness and defects that cause non-radiative recombination. It is revealed that the physical polishing can reduce the root mean square roughness from 15.9 nm to 1.2 nm, facilitating the screen printing of the C electrode. The carrier lifetime of the PVK film also increases from 39.9 ns to 73.3 ns, which improves the photocurrent of the solar cell. We believe that the improved C/PVK interface contact will provide a solid foundation for the future large-scale commercial production of PSCs.