Initial Power Conversion Efficiency Research Articles

Eliminating Voids and Residual PbI2 beneath a Perovskite Film via Buried Interface Modification for Efficient Solar Cells.

The commercialization process of perovskite solar cells (PSCs) is markedly restricted by the power conversion efficiency (PCE) and long-term stability. During fabrication and operation, the bottom interface of the organic-inorganic hybrid perovskite layer frequently exhibits voids and residual PbI2, while these defects inevitably act as recombination centers and degradation sites, affecting the efficiency and stability of the devices. Therefore, the degradation and nonradiative recombination originating from the buried interface should be thoroughly resolved. Here, we report a multifunctional passivator by introducing malonic dihydrazide as an interfacial chemical bridge between the electron transport layer and the perovskite (PVK) layer. MADH with hydrazine groups improves the surface affinity of SnO2 and provides nucleation sites for the growth of PVK, leading to the reduced residual PbI2 and the voids resulting from the inhomogeneous solvent volatilization at the bottom interface. Meanwhile, the hydrazine group and carbonyl group synergistically coordinate with Pb2+ to improve the crystal growth environment, reducing the number of Pb-related defects. Eventually, the PCE of the PSCs is significantly enhanced benefiting from the reduced interfacial defects and the increased carrier transport. Moreover, the reductive nature of hydrazide further inhibits I2 generation during long-term operation, and the device retains 90% of the initial PCE under a 1 sun continuous illumination exposure of 700 h.

Improving Buried Interface Contact by Bidentate Anchoring for Inverted Perovskite Solar Cells.

Nickel oxide (NiOx) is a promising hole transport layer (HTL) to fabricate efficient and large-scale inverted perovskite solar cells (PSCs) due to its low cost and superior chemical stability. However, inverted PSCs based on NiOx are still lagging behind that of other HTL because of the poor quality of buried interface contact. Herein, a bidentate ligand, 4,6-bis (diphenylphosphino) phenoxazine (2DPP), is used to regulate the NiOx surface and perovskite buried interface. The diphosphine Lewis base in the 2DPP molecule can coordinate both with NiOx and lead ions at NiOx/perovskite interface, leading to high-quality perovskite films with minimized defects. It is found that the inverted PSCs with 2DPP-modified buried interface exhibit double advantages of being both fast charge extraction and reduced nonradiative recombination, which is a combination of multiple factors including favorable energetic alignment, improved interface contact and strong binding between NiOx/2DPP and perovskite. The optimal PSC based on 2DPP modification yields a champion power conversion efficiency (PCE) of 21.9%. The unencapsulated PSC maintains above 75% of its initial PCE in the air with a relative humidity (RH) of 30-40% for 1000h.

Stereoscopic Polymer Network for Developing Mechanically Robust Flexible Perovskite Solar Cells with an Efficiency Approaching 25.

Flexible perovskite solar cells (pero-SCs) have the potential to overturn the application scenario of silicon photovoltaic technology. However, their mechanical instability severely impedes their practical applicability, and the corresponding intrinsic degradation mechanism remains unclear. In this study, the degradation behavior of flexible pero-SCs is systematically analyzed under mechanical stress and it is observed that the structural failure first occurs in the polycrystal perovskite film, then extend to interfaces. To suppress the structural failure, pentaerythritol triacrylate, a crosslinked molecule with three stereoscopic crosslink sites, is employed to establish a 3D polymer network in both the interface and bulk perovskite. This network reduced the Young's modulus of the perovskite and simultaneously enhanced the interfacial toughness. As a result, the formation of cracks and delamination, which occur under a high mechanical stress, is significantly suppressed in the flexible pero-SC, which consequently retained 92% of its initial power conversion efficiency (PCE) after 20000 bending cycles. Notably, the flexible device also shows a record PCE of 24.9% (certified 24.48%).

Mitigating the Degradation of MAPbI3 Perovskite Solar Cells Under Continuous Light Soaking with ZnO@CdS:Epoxy Short‐Wavelength Sunlight‐Shielded Films

The stability of MAPbI3‐based (MA stands for methylammonium) perovskite solar cells (PVSCs) has been carefully examined by ZnO@CdS nanoparticle‐embedded epoxy films (EP‐ZC films), device encapsulation (of glass sheet and UV‐curing gel), and in different temperatures, 10 °C, room temperature (no temperature control), and 65 °C. EP‐ZC films are used for shielding the short wavelength of the sunlight (UV, near UV, violet, and deep blue) which causes the photodegradation of MAPbI3 and hence the decline of power conversion efficiency (PCE) of PVSCs. Some external quantum efficiency spectra of the device are recorded alongside of the 500 h continuous light‐soaking measurement of current density (J)−voltage (V) of the devices. The time‐of‐flight secondary‐ion mass spectroscopy analysis is performed for a quantitative comparison of the iodide derived from the degradation of MAPbI3 in the encapsulated devices with or without the light‐shielding EP‐ZC films at 10 °C and 65 °C, respectively. The EP‐ZC6 film shows the best protection for encapsulated PVSCs with 98% of the initial PCE at 10 °C after 500 h continuous light soaking. Herein, from the continuous light‐soaking results, one can prioritize the moisture, temperature, and light in the influence of the stability of PVSCs.

Work Function Tuning of Carbon Electrode to Boost the Charge Extraction in Hole Transport Layer-Free Perovskite Solar Cells.

Perovskite solar cell (PSC) is a promising photovoltaic technology that achieves over 26% power conversion efficiency (PCE). However, the high materials costs, complicated fabrication process, as well as poor long-term stability, are stumbling blocks for the commercialization of the PSCs in normal structures. The hole transport layer (HTL)-free carbon-based PSCs (C-PSCs) are expected to overcome these challenges. However, C-PSCs have suffered from relatively low PCE due to severe energy loss at the perovskite/carbon interface. Herein, the study proposes to boost the hole extraction capability of carbon electrode by incorporating functional manganese (II III) oxide (Mn3O4). It is found that the work function (WF)of the carbon electrode can be finely tuned with different amounts of Mn3O4 addition, thus the interfacial charge transfer efficiency can be maximized. Besides, the mechanical properties of carbon electrode can also be strengthened. Finally, a PCE of 19.03% is achieved. Moreover, the device retains 90% of its initial PCE after 2000 h of storage. This study offers a feasible strategy for fabricating efficient paintable HTL-free C-PSCs.

SnSe2 Quantum Dots and Chlorhexidine Acetate Suppress Synergistically Non-radiative Recombination Loss for High Efficiency and Stability Perovskite Solar Cells.

Non-radiative recombination losses limit the property of perovskite solar cells (PSCs). Here, a synergistic strategy of SnSe2QDs doping into SnO2 and chlorhexidine acetate (CA) coating on the surface of perovskite is proposed. The introduction of 2D SnSe2QDs reduces the oxygen vacancy defects and increases the carrier mobility of SnO2. The optimized SnO2 as a buried interface obviously improves the crystallization quality of perovskite. The CA containing abundant active sites of ─NH2/─NH─, ─C═N, CO, ─Cl groups passivate the defects on the surface and grain boundary of perovskite. The alkyl chain of CA also improves the hydrophobicity of perovskite. Moreover, the synergism of SnSe2QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite. Benefiting from these advantages, the bulk and interface non-radiative recombination loss is greatly suppressed and thereby increases the carrier transport and extraction in devices. As a result, the best power conversion efficiency (PCE) of 23.41% for rigid PSCs and the best PCE of 21.84% for flexible PSCs are reached. The rigid PSC maintains 89% of initial efficiency after storing nitrogen for 3100 h. The flexible PSCs retain 87% of the initial PCE after 5000 bending cycles at a bending radius of 5 mm.

Interfacial engineering with a ferrocene derivative for air-stable inverted perovskite solar cells with high fill factor of 83.57 %

Perovskite solar cells have demonstrated exceptional photovoltaic performance, but stability remains a challenge due to insufficient interfaces. In this work, a UV-resistance ferrocene derivative, 1,1′-bis (diphenylphosphine) ferrocene (DPPF), is introduced between the electron transport layer and the perovskite, reducing defect density by interaction with undercoordinated Pb2+, suppressing non-radiative recombination of charge carriers, and enhancing electron extraction. Desirable interfacial properties and homogeneous perovskite grains are formed, resulting in a champion power conversion efficiency (PCE) of 20.82 % and a significantly improved fill factor of 83.57 %. Moreover, DPPF can optimize the interfaces, provide a brand-new morphology with exceptional air durability, cover the active layer to restrain water and oxygen intrusion, and suppress metal electrode corrosion. Resultant devices without encapsulation have remained above 80 % of their initial PCE for 1400 h under 25 °C air and 50–60 % relative humidity conditions.

Efficient and Highly Stable Lateral Perovskite Single‐Crystal Solar Cells through Crystal Engineering and Weak Ion Migration

AbstractThe lateral device structure for perovskite solar cells (PSCs) has garnered significant attention, primarily due to its elimination of the need for expensive transparent electrodes. However, the performance of lateral devices, which are more sensitive to crystal quality and charge carrier transport bottlenecks, has lagged far behind the predominant vertical PSCs. Herein, by modulating the crystal nucleation and growth processes of thin FA0.75MA0.25PbI3 (FA = formamidinium; and MA = methylammonium) single crystals, crystal quality and carrier transport are improved, resulting in a power conversion efficiency (PCE) of 12.64%, a record for lateral PSCs. Investigation of the device's stability reveals that iodide ion migration is suppressed due to a reduction in the iodide vacancy concentration combined with weak interface iodide ion migration. It is shown that the latter effect is a result of the perpendicular direction of the ion migration and the electric field in the lateral PSCs. Consequently, these lateral single‐crystal PSCs display remarkable operational stability, retaining 100% of their initial PCE after 1200 h of steady‐state output at the maximum power point voltage (Vmpp) under 1 sun illumination. This work highlights the advantages of lateral single‐crystal devices and their potential to address key ion migration issues of PSCs.

Precursor-Engineered Volatile Inks Enable Reliable Blade-Coating of Cesium-Formamidinium Perovskites Toward Fully Printed Solar Modules.

Reliable fabrication of large-area perovskite films with antisolvent-free printing techniques requires high-volatility solvents, such as 2-methoxyethanol (2ME), to formulate precursor inks. However, the fabrication of high-quality cesium-formamidinium (Cs-FA) perovskites has been hampered using volatile solvents due to their poor coordination with the perovskite precursors. Here, this issue is resolved by re-formulating a 2ME-based Cs0.05FA0.95PbI3 ink using pre-synthesized single crystals as the precursor instead of the conventional mixture of raw powders. The key to obtaining high-quality Cs-FA films lies in the removal of colloidal particles from the ink and hence the suppression of colloid-induced heterogeneous nucleation, which kinetically facilitates the growth of as-formed crystals toward larger grains and improved film crystallinity. Employing the precursor-engineered volatile ink in the vacuum-free, fully printing processing of solar cells (with carbon electrode), a power conversion efficiency (PCE) of 19.3%, a T80 (80% of initial PCE) of 1000h in ISOS-L-2I (85°C/1Sun) aging test and a substantially reduced bill of materials are obtained. The reliable coating methodology ultimately enables the fabrication of carbon-electrode mini solar modules with a stabilized PCE of 16.2% (average 15.6%) representing the record value among the fully printed counterparts and a key milestone toward meeting the objectives for a scalable photovoltaic technology.

Asymmetrical benzothiadiazole core-based hole transport materials for planar perovskite solar cell

For the purpose of fabricating high performance hole transport materials (HTMs) for n-i-p planar perovskite solar cells (PSCs), two asymmetric and one symmetric structured donor-acceptor-donor (D-A-D) type small molecules (a-BTC, a-BTBC and BTDC) were synthesized by introducing two different peripheral groups toward benzothiadiazole core. The a-BTBC with longer π conjugation lengths shows good film formation property, higher hole mobility and conductivity, and achieves power conversion efficiency (PCE) of 23.5 %. It can retain 80 % of the initial PCE after aging 30 days in an ambient condition with relative humidity of 40–60 %. Our results show the potential and provides reference for molecular design of asymmetric structured HTMs.

Crystallization management and defect passivation via additive engineering for efficient and stable carbon-based CsPbI2Br perovskite solar cells

Inorganic CsPbI2Br perovskite solar cells (PSCs) have attracted enormous interest due to their excellent thermal stability and immense potential for application in tandem solar cells. However, the rambunctious crystallization and poor film quality of inorganic CsPbI2Br perovskite are the main factors limiting their performance improvement. Herein, dibenzoylmethane (DBM), containing electron-rich and dual CO functional groups, as an efficient precursor additive, is first introduced to regulate the crystallization of CsPbI2Br perovskite while passivating its associated defects. After DBM modification, nucleation is accelerated and the crystallinity of CsPbI2Br film is improved, thus promoting the phase stability. Additionally, DBM can passivate uncoordinated Pb2+ defects, thereby significantly reducing non-radiative recombination, and can also decrease the energy level difference between CsPbI2Br/Carbon. As a result, when DBM additive is incorporated in the CsPbI2Br, the power conversion efficiency (PCE) of the device with the fluorine doped tin oxide glass (FTO)/SnO2/CsPbI2Br/Carbon structure is significantly improved to 13.46 %, an increase of nearly 13 % compared to the control device (11.72 %). The unpackaged devices exhibit excellent air and thermal stability, still remaining over 90 % of its initial PCE after aging for 500 h under ambient conditions, or continuous heating at 65 °C in glovebox for 500 h, respectively.

Narrow bandgap Sn-Pb perovskite solar cells with high operational stability modulated by imidazoline derivative

Sn-Pb mixed perovskites with narrow bandgap (NBG) are important for high-performance single- and multi-junction perovskite solar cells (PSCs). However, the inherent Sn2+ oxidation and ion migration lead to inferior stability. Herein, 2-hydrazino-2-imidazoline hydrobromide (2H2I) is employed as a coordinating additive to regulate the film crystallization and inhibit Sn2+ oxidation. Meanwhile, 2H2I can form hydrogen bonds with I− ions to suppress ion migration, thereby improving photovoltaic stability. The target FA0.8Cs0.2Sn0.5Pb0.5I3:2H2I PSC exhibits a champion power conversion efficiency (PCE) of 22.44 %, higher than that of the control device (19.16 %). The target devices retain 90 % (T90) and 80 % (T80) of the initial PCE under maximum power point (MPP) tracking for 1360 h at room temperature and for 436 h at 65 °C, respectively, the highest values for NBG Sn-Pb PSCs. This work demonstrates an effective strategy toward photothermally stable Sn-Pb PSCs.

A Fluorination Strategy and Low-Acidity Anchoring Group in Self-Assembled Molecules for Efficient and Stable Inverted Perovskite Solar Cells.

Herein, we synthesized two donor-acceptor (D-A) type small organic molecules with self-assembly properties, namely MPA-BT-BA and MPA-2FBT-BA, both containing a low acidity anchoring group, benzoic acid. After systematically investigation, it is found that, with the fluorination, the MPA-2FBT-BA demonstrates a lower highest occupied molecular orbital (HOMO) energy level, higher hole mobility, higher hydrophobicity and stronger interaction with the perovskite layer than that of MPA-BT-BA. As a result, the device based-on MPA-2FBT-BA displays a better crystallization and morphology of perovskite layer with larger grain size and less non-radiative recombination. Consequently, the device using MPA-2FBT-BA as hole transport material achieved the power conversion efficiency (PCE) of 20.32 % and remarkable stability. After being kept in an N2 glove box for 116 days, the unsealed PSCs' device retained 93 % of its initial PCE. Even exposed to air with a relative humidity range of 30±5 % for 43 days, its PCE remained above 91 % of its initial condition. This study highlights the vital importance of the fluorination strategy combined with a low acidity anchoring group in SAMs, offering a pathway to achieve efficient and stable PSCs.

Design tungsten oxides hole transport layers (HTLs) to modify the back interface in all-inorganic carbon-based CsPbBr3 solar cells

To enhance the inferior photovoltaic performance of all-inorganic carbon-based perovskite solar cells (C-PSCs) caused by inefficient charge extraction and transport processes of the CsPbBr3/carbon back interface, three types of tungsten oxides (WO3, WO2.72, WO2) are synthesized as low cost and stable hole transport layers (HTLs) to modify the back interface by tunning the energy level alignment. Among the three kinds of tungsten oxides, WO3 shows the best hole extraction and transport capability and the C-PSCs using WO3 HTL generates a power conversion efficiency (PCE) of 7.90% with a high open circuit voltage (Voc) of 1.307 V, indicating a great PCE enhancement of 43.9%, as compared with the device without HTL (5.49%). Meanwhile, WO2.72 and WO2 also are also proved to be qualified HTLs and the devices show PCE values of 7.57% and 6.24%, respectively. Importantly, WO3 and WO2.72 based device show excellent stabilities with PCE retention over 90% of the initial PCE values under ambient conditions for 60 days.

A Synergistic Effect among Multiple Functional Groups of 4‐PyAO Additive for Performance Enhancement of Tin‐Based Perovskite Solar Cells

Tin‐based perovskite is a competitive analog with lead halide perovskite, but there are significant gaps in power conversion efficiency (PCE) and stability between tin‐ and lead‐based perovskite solar cells. The characteristics of the easy oxidizability of Sn2+ and the rapid crystal growth for tin‐based perovskite are two major issues remained to be overcome. Herein, an additive (4‐pyridylamidoxime (4‐PyAO)) with multiple functional groups is introduced in the perovskite precursor solution. The oxidation of Sn2+ and the crystallization rate of perovskite are both retarded by 4‐PyAO addition. The prepared perovskite film is of high quality with fewer trap states and carrier recombination, and carrier extraction and transfer between the perovskite film and the adjacent carrier transport layer also become more efficient. As a result, the corresponding devices deliver the highest PCE of 9.02%, accompanied by short‐circuit current density, open‐circuit voltage, and fill factor of 19.90 mA cm−2, 0.63 V, and 72.48%, respectively. More importantly, the best device without encapsulation maintains 92% of its initial PCE after 2500 h aging test in nitrogen atmosphere, which may be attributed to a synergic effect among the different functional groups.

Fullerene derivatives barrier layer for efficient and stable perovskite solar cells through interfacial modification and removal of superoxide radicals

Superoxide radicals(O2•–)-induced decomposition of perovskite, which seriously impairs the photovoltaic performance and stability of perovskite solar cells (PSCs). Both TiO2 and perovskite produce O2•– that accelerates the rate of catalytic degradation at the interface and inherently poor interfacial contact, exacerbating charge recombination and efficiency loss. Adding fullerene phenol derivative (C60HTB) to the perovskite/TiO2 interface absorbs O2•– and improves poor interfacial communication. The PSCs' power conversion efficiency (PCE) is improved from 20.54 % to 21.63 %. The target devices retained 91.20 %, 94.86 %, and 89.36 % of their initial power conversion efficiencies after 48 h of aging under full-spectrum illumination, 240 h of aging under ultraviolet illumination, and dark storage in air for 500 h, respectively. In this work, efficient and stable TiO2-based-PSCs were realized by scavenging O2•–, which opens a new way to enhance the stability of PSCs in light and O2 environments (light/oxygen).

Performance and stability of hybrid organic-inorganic perovskite photovoltaics in outdoor illuminations conditions

In this study, we conducted real-world outdoor performance and stability tests on two different configurations of perovskite solar cells in the climate conditions of Bahir Dar, Ethiopia. Under outdoor illumination with an incident power of 69 mW cm−2, this device demonstrated a power conversion efficiency (PCE) of 15% for an active area of 0.1 cm2. The maximum power generated, measured at a solar irradiance of 72 mW/ cm2, and was 1.23 mW. The second perovskite device has planar p-i-n configuration. This device achieved a PCE of 18% without masking, but the PCE dropped to 11% when the device was covered with circular aperture mask. Maximum power tracking and stability measurements of the device were conducted. Maximum power generation occurred at operating voltages ranging from 0.8 V to 1.2 V for a device with an active area of 0.095 to 0.1cm2. After 30 days of environmental exposure, the device maintained more than 90% of its initial PCE.

A novel chain-like conjugated donor-π-acceptor molecular additive for highly efficient and stable perovskite solar cells

In donor-π-acceptor (D-π-A) molecules, the coordination ability of the acceptor can be enhanced by the directed movement of delocalized electrons (DEs) on the π-bridge. However, the conventional aromatic ring as π-bridge limits the number of DEs due to the structural characteristic, which restrict the coordination ability of the acceptor, and there is still a lack of research on this issue. Herein, we proposed a chain-like conjugated π-bridge design strategy to address this issue. The Astaxanthin with eleven contiguous C − C = C fragments was selected as a chain-like D-π-A additive for perovskite films. Twenty-two DEs in such chain-like bridge can move towards the C = O group by the D-π-A effect within Astaxanthin, which increases the electron cloud density of C = O group so that enhances its coordination capacity with cations. Ultimately, the Astaxanthin-based device achieved a champion power conversion efficiency (PCE) of 24.43 % and maintained more than 95 % and 91 % of initial PCE for aging 1000 h in dry air (RH < 1 %) and atmosphere (RH = 20 ∼ 30 %), respectively. This work provides a novel strategy to break the restriction of aromatic rings to DEs, which provides theoretical and experimental guidance for further designing chain-like D-π-A additives with strong defect passivation ability to boost photovoltaic performance of PSCs.

Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV.

The achievement of both efficiency and stability in perovskite solar cells (PSCs) remains a challenging and actively researched topic. In particular, among different environmental factors, ultraviolet (UV) photons play a pivotal role in contributing to device degradation. In this work, by harvesting simultaneously both the optical and the structural properties of bottom-up-synthesized colloidal carbon quantum dots (CQDs), a cost-effective means is provided to circumvent the UV-induced degradation in PSCs without scarification on their power conversion efficiencies (PCEs). By exploring and optimizing the number of CQDs and the different locations/interfaces of the solar cells where CQDs are applied, a synergetic configuration is achieved where the photovoltaic performance drop due to optical loss is completely compensated by the increased perovskite crystallinity due to interfacial modification. As a result, on the optimized configurations where CQDs are applied both on the exterior front side as an optical layer and at the interface between the electron transport layer and the perovskite absorber, unencapsulated PSCs with PCEs >20% are fabricated which can maintain up to ≈94% of their initial PCE after 100h of degradation in ambient air under continuous UV illumination (5mWcm-2).

A Pseudo Planar Heterojunction Structure for Eco‐Friendly Printable Organic Solar Cells Achieving 19.05% Efficiency

AbstractObtaining a well‐accurate vertical distribution active layer morphology through the air‐printing process is an essential task for achieving efficient scalable large‐area organic solar cells (OSCs). In this target, the desired and controllable pseudo planar heterojunction (PPHJ) active layer structure with suitable phase separation is developed by pre‐deposited D18‐Cl layer under the PM6:BTP‐eC9 film via an eco‐friendly manufacturing method. The addition of the D18‐Cl regulates molecular crystallization and leads to an ideal vertical stratification while simultaneously suppressing voltage loss, optimizing energetic disorder, and carrier management. Impressively, the optimal PPHJ devices perform superior power conversion efficiencies (PCEs) of 19.05% (100 nm), 17.33% (300 nm), and 14.14% (4 cm2) compared to the BHJ devices. Importantly, the PPHJ OSCs also exhibit an impressive extrapolated T80 (the time required to reach 80% of initial PCE) of long‐time storage and operational stability, as well as thermal stability.