Chen Weijie

Degradation of perovskite solar cells (PSCs) with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobi-fluorene (spiro-OMeTAD) in air is investigated. The hole-transport level deepening in spiro-OMeTAD under air exposure decreases the performance of PSCs over time because of an increase in hole-extraction barrier at the perovskite/spiro-OMeTAD interface. However, the PSCs performance recovers after the degasification of oxygen by storing the air-exposed devices in a vacuum overnight.

After remarkable progress over the past decades, perovskite solar cells (PSCs) currently exhibit efficient solar power conversion efficiency. However, the environmental instability of perovskite materials and devices is still a serious issue, impeding the future commercialization of this technology. Herein, why PSCs degrade in air is investigated and it is found that one of the critical reasons for the air-induced PSC degradation is the doping of the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobi-fluorene (spiro-OMeTAD) hole-transport layer with oxygen. Photoelectron yield spectroscopy reveals that the hole-transport level of the spiro-OMeTAD layer becomes deeper by oxygen doping, increasing an energy barrier for hole extraction. In other words, decreased hole extraction at the perovskite/spiro-OMeTAD interface induces the degradation of PSCs in air. However, this oxygen-induced degradation of PSCs is reversible to some extent by storing PSCs in a vacuum to remove oxygen. In contrast, no detectable degradation of the perovskite light absorber is observed after ≈600 h of air exposure from the results of morphological and structural characterizations. These aspects provide a deeper understanding of PSCs degradation, giving insight into improving long-term durability in air in the future.

This work presents a new strategy to improve the performance of perovskite solar cells by doping streptomycin sulfate (STRS) into a SnO₂ ETL. The multiple functions of STRS make the efficiency of the rigid device up to 22.89%, and the efficiency of the flexible device up to 20.79%, and both have excellent stability.

Abstract

SnO₂ as an electron transport layer (ETL) has been widely used in regular planar perovskite solar cells (PSCs) owing to its high optical transmittance, less photocatalytic activity, and low-temperature processing. However, SnO₂-based PSCs still face many challenges which greatly impair their efficiency and stability of PSCs. Herein, a novel and effective multifunctional modification strategy is proposed by incorporating streptomycin sulfate (STRS) molecules with multiple functional groups into SnO₂ ETL. STRS can significantly suppress SnO₂ nanoparticle agglomeration, improve the electronic property of SnO₂, as well as reduce nonradiative recombination. At the same time, interfacial residual tensile stress is released and the interfacial energy level alignment becomes more matched. As a result, the STRS-modified PSCs achieve a higher efficiency of 22.89% compared to 20.61% of the control device and exhibit a hysteresis-free feature. The humidity and thermal stability of PSCs based on STRS-SnO₂ are significantly improved. Furthermore, the efficiency of flexible devices increased from 19.74% to 20.79%, and the devices still maintain >80% of initial PCE after 4500 bending cycles with a bend radius of 5 mm. This study provides a low-cost, facile, and efficient strategy for achieving high efficiency and stability in PSCs.

Using molecular self-assembly strategy effectively passivates the interfacial defects at the FAPbBr₃ film surface, resulting in enhancement of the photovoltaic performance of wide bandgap FAPbBr₃ perovskite, especially in low-light environments. More importantly, this report also demonstrates the considerable potential of FAPbBr₃ solar cells for underwater photovoltaic applications.

Abstract

Underwater solar cells (UWSCs) provide an ideal alternative to the energy supply for long-endurance autonomous underwater vehicles. However, different from conventional solar cells situated on land or above water, UWSCs give preference to use wide bandgap semiconductors (≥1.8 eV) as light absorber to match underwater solar spectra. Among wide bandgap semiconductors, FAPbBr₃ perovskite is under prime consideration owing to its matching optical bandgap (≈2.3 eV), outstanding photoelectric properties, easier processability, etc. Unfortunately, for FAPbBr₃ solar cells, substantial interface defects greatly limit the charge carrier extraction efficiency, thus limiting the device performance, especially in underwater low-light environments. This study employs a molecular self-assembly strategy to effectively eliminate the interfacial defects. As a result, a great improvement in power conversion efficiency (PCE) from 6.44% to 7.49% is obtained, which is among the best efficiency reported for inverted FAPbBr₃ solar cells up to date. Besides, a champion PCE of 30% is obtained under 520 nm monochromatic light irradiation (4.8 mW cm⁻²). These results demonstrate that FAPbBr₃ solar cells present a tremendously promising application in UWSCs.

Monolithic Cu(In,Ga)Se₂ (CIGSe)-perovskite tandem solar cells (23.4%-efficient) manufactured on CIGSe absorbers with a non-negligible surface roughness is demonstrated. Conformal coverage of the bottom sub-cell, shunt prevention and high effective lifetime in the top cell, and fast hole extraction, favorable band alignment, and suppressed electron trapping at the HTL-perovskite interface are achieved by using copper-doped nickel oxide NiO _x :Cu + [2-(3,-6Dimethoxy-9H-carbazol-9yl)ethyl]phosphonic acid (MeO-2PACz) as a hole-transporting bi-layer.

Abstract

The performance of five hole-transporting layers (HTLs) is investigated in both single-junction perovskite and Cu(In, Ga)Se₂ (CIGSe)-perovskite tandem solar cells: nickel oxide (NiO _x ,), copper-doped nickel oxide (NiO _x :Cu), NiO _x +SAM, NiO _x :Cu+SAM, and SAM, where SAM is the [2-(3,-6Dimethoxy-9H-carbazol-9yl)ethyl]phosphonic acid (MeO-2PACz) self-assembled monolayer. The performance of the devices is correlated to the charge-carrier dynamics at the HTL/perovskite interface and the limiting factors of these HTLs are analyzed by performing time-resolved and absolute photoluminescence ((Tr)PL), transient surface photovoltage (tr-SPV), and X-ray/UV photoemission spectroscopy (XPS/UPS) measurements on indium tin oxide (ITO)/HTL/perovskite and CIGSe/HTL/perovskite stacks. A high quasi-Fermi level splitting to open-circuit (QFLS-V _oc ) deficit is detected for the NiO _x -based devices, attributed to electron trapping and poor hole extraction at the NiO _x -perovskite interface and a low carrier effective lifetime in the bulk of the perovskite. Simultaneously, doping the NiO _x with 2% Cu and passivating its surface with MeO-2PACz suppresses the electron trapping, enhances the holes extraction, reduces the non-radiative interfacial recombination, and improves the band alignment. Due to this superior interfacial charge-carrier dynamics, NiO _x :Cu+SAM is found to be the most suitable HTL for the monolithic CIGSe-perovskite tandem devices, enabling a power-conversion efficiency (PCE) of 23.4%, V _oc of 1.72V, and a fill factor (FF) of 71%, while the remaining four HTLs suffer from prominent V _oc and FF losses.

The effects of energy offset and defects with different halide types in 2D perovskite are studied, providing a new approach for designing stable and efficient PSCs. Using 2D/3D perovskite heterojunctions can improve the passivation and charge-carrier extraction, boosting the efficiency to 25.32% for the small devices and 21.48% for the large module.

Abstract

Currently, the full potential of perovskite solar cells (PSCs) is limited by chargecarrier recombination owing to imperfect passivation methods. Here, the recombination loss mechanisms owing to the interfacial energy offset and defects are quantified. The results show that a favorable energy offset can reduce minority carriers and suppress interfacial recombination losses more effectively than chemical passivation. To obtain high-efficiency PSCs, 2D perovskites are promising candidates, which offer powerful field effects and require only modest chemical passivation at the interface. The enhanced passivation and charge-carrier extraction offered by the 2D/3D heterojunction PSCs has boosted their power conversion efficiency to 25.32% (certified 25.04%) for small-size devices and to 21.48% for a large-area module (with a designated area of 29.0 cm²). Ion migration is also suppressed by the 2D/3D heterojunction, such that the unencapsulated small-size devices maintain 90% of their initial efficiency after 2000 h of continuous operation at the maximum power point.

Improving the homogeneity of the active layer is critical to reduce cell-to-module loss. Coffee ring is suppressed with an airflow-assisted slot-die technique to overcome efficiency loss. A notable power conversion efficiency of 13.08% is obtained in 30 cm² flexible organic solar modules, maintaining 95% of 1 cm² device, which is the minimum power conversion efficiency loss from 1 cm² to large-area devices.

As a roll-to-roll compatible technology, slot-die coating has shown great potential for manufacturing industrial-level organic solar cells (OSCs). However, in the slot-die coatings process, coffee rings are often formed due to the slow film-forming kinetics, leading to a significant loss of power conversion efficiency (PCE) in upscaling device area. Herein, the coffee rings are suppressed by introducing an airflow-assisted slot-die technique to obtain a suitable active layer morphology with improved flatness and homogeneity. Synergistically, optimization of airflow and substrate temperature conditions, the PCE of 1 cm² flexible OSC devices reaches 13.69%. Moreover, large-area flexible OSC modules with 30 cm² achieve a PCE of 13.08%, maintaining 95% of 1 cm² device, which is the minimum PCE loss from 1 cm² to large-area devices. Morphology characterization shows that airflow can suppress excessive molecular aggregation and obtain suitable phase separation. Therefore, this work provides an efficient method to fabricate high-efficiency flexible large-area OSC modules, which will promote OSC devices from lab to fab.

An ultrathin self-assembled ionic insulating layer mitigates ion migration in wide-bandgap inverted perovskite solar cells. As a result, halide phase segregation is significantly inhibited, thus reducing V _OC loss and improving the efficiency and stability of the devices.

Abstract

Wide-bandgap perovskite solar cells (PSCs) are attracting increasing attention because they play an irreplaceable role in tandem solar cells. Nevertheless, wide-bandgap PSCs suffer large open-circuit voltage (V _OC) loss and instability due to photoinduced halide segregation, significantly limiting their application. Herein, a bile salt (sodium glycochenodeoxycholate, GCDC, a natural product), is used to construct an ultrathin self-assembled ionic insulating layer firmly coating the perovskite film, which suppresses halide phase separation, reduces V _OC loss, and improves device stability. As a result, 1.68 eV wide-bandgap devices with an inverted structure deliver a V _OC of 1.20 V with an efficiency of 20.38%. The unencapsulated GCDC-treated devices are considerably more stable than the control devices, retaining 92% of their initial efficiency after 1392 h storage under ambient conditions and retaining 93% after heating at 65 °C for 1128 h in an N₂ atmosphere. This strategy of mitigating ion migration via anchoring a nonconductive layer provides a simple approach to achieving efficient and stable wide-bandgap PSCs.

Asymmetric FPy unit is proposed to control the aggregation and fibril network of polymer blends. The resulting organic solar cells (OSCs) exhibit high power conversion efficiency (PCE) and reproducibility. Semi-transparent OSCs (ST-OSCs) with high light utilization efficiencies are obtained. Large I-OSC is achieved with a high PCE. The long-term stability of devices is evaluated based on its structure. This work realizes eco-friendly, efficient, and stable OSCs/ST-OSCs/I-OSCs.poly((4,8-bis(5-(2-ethylhexyl)-4-fluoro-2-thienyl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)-2,5-thiophenediyl(5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl)-2,5-thiophenediyl)

Abstract

The development of eco-friendly solvent-processed organic solar cells (OSCs) suitable for industrial-scale production should be now considered the imperative research. Herein, asymmetric 3-fluoropyridine (FPy) unit is used to control the aggregation and fibril network of polymer blends. Notably, terpolymer PM6(FPy = 0.2) incorporating 20% FPy in a well-known donor polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)] (PM6) can reduce the regioregularity of the polymer backbone and endow them with much-enhanced solubility in eco-friendly solvents. Accordingly, the excellent adaptability for fabricating versatile devices based on PM6(FPy = 0.2) by toluene processing is demonstrated. The resulting OSCs exhibit a high power conversion efficiency (PCE) of 16.1% (17.0% by processed with chloroform) and low batch-to-batch variation. Moreover, by controlling the donor-to-acceptor weight ratio at 0.5:1.0 and 0.25:1.0, semi-transparent OSCs (ST-OSCs) yield significant light utilization efficiencies of 3.61% and 3.67%, respectively. For large-area (1.0 cm²) indoor OSC (I-OSC), a high PCE of 20.6% is achieved with an appropriate energy loss of 0.61 eV under a warm white light-emitting diode (3,000 K) with the illumination of 958 lux. Finally, the long-term stability of the devices is evaluated by investigating their structure–performance–stability relationship. This work provides an effective approach to realizing eco-friendly, efficient, and stable OSCs/ST-OSCs/I-OSCs.

The bilayer SnO₂ layers are applied into Perovskite solar cells (PSCs) as prominent electron transport layers (ETLs) successfully addressed the common issues from conventional SnO₂ ETL with sol–gel solution. Moreover, the bilayer SnO₂ ETLs result in a distinct increase in power conversion efficiency (PCE) and stability of ionic liquid-based PSCs with two-step approach.

Abstract

Perovskite solar cells (PSCs) based on the SnO₂ electron transport layer (ETL) have achieved remarkable photovoltaic efficiency. However, the commercial SnO₂ ETLs show various shortcomings. The SnO₂ precursor is prone to agglomeration, resulting in poor morphology with numerous interface defects. Additionally, the open circuit voltage (V _oc) would be constrained by the energy level mismatch between the SnO₂ and the perovskite. And, few studies designed SnO₂-based ETLs to promote crystal growth of PbI₂, a crucial prerequisite for obtaining high-quality perovskite films via the two-step method. Herein, we proposed a novel bilayer SnO₂ structure that combined the atomic layer deposition (ALD) and sol-gel solution to well address the aforementioned issues. Due to the unique conformal effect of ALD-SnO₂, it can effectively modulate the roughness of FTO substrate, enhance the quality of ETL, and induce the growth of PbI₂ crystal phase to develop the crystallinity of perovskite layer. Furthermore, a created built-in field of the bilayer SnO₂ can help to overcome the electron accumulation at the ETL/perovskite interface, leading to a higher V _oc and fill factor. Consequently, the efficiency of PSCs with ionic liquid solvent increases from 22.09% to 23.86%, maintaining 85% initial efficiency in a 20% humidity N2 environment for 1300 h.

A selenium-containing non-fullerene acceptor is synthesized and used for constructing photomultiplication organic photodetectors. Remarkable photomultiplication effects with a broadband spectral range is observed and the effect of atomic substitution on the morphology is studied. The optimized molecular arrangement ensures strong charge trapping and finer phase separation between the donor and acceptor molecules facilitates hole trapping, thereby strengthening the photomultiplication effects.

Abstract

Organic photodetectors (OPDs) with spectral response extending from ultraviolet to near-infrared domains are of great interest for many applications. Morphological impact on the performance of photomultiplication (PM)-type OPDs, however, is still rarely investigated so far. Herein, a non-fullerene acceptor, Y6-Se-HD, is synthesized, in which heavier selenium atoms substitute the sulfur atoms in the core of Y6, and used for fabricating PM-OPDs. The resulting devices exhibit remarkable PM effects in a very broadband spectral range covering from 320 to 1090 nm. A maximum EQE value of ≈6500% at 860 nm is achieved at a low bias of −1.0 V. As compared with the device prepared with Y6 molecules, the Y6-Se-HD OPDs exhibited much enhanced performance. From the morphological analysis, we infer that Y6-Se-HD almost covers the entire active layer and avoids the direct contact of the hole-trapping donor polymers with the Ag electrode, thereby resulting in stronger charge trapping and preventing possible charge recombination and/or quenching. Furthermore, finer phase separation between the donor and acceptor molecules also facilitates hole trapping and strengthens the PM effects. This research highlights the importance of morphological effects on the PM-OPDs and demonstrates one approach for controlling the device morphology.

A dual-additive-driven morphology optimization method is developed for all-small-molecule organic solar cells based on BTR-Cl:Y6. The solid additive DIB and liquid additive DIM are incorporated to synergistically control the active layer morphology through their distinct interaction mechanisms with Y6 and BTR-Cl, resulting in a high PCE of 15.2% for all-small-molecule organic solar cells without solvent annealing treatment.

Abstract

All-small-molecule organic solar cells (ASM-OSCs), which consist of small-molecule donors and acceptors, have recently been studied extensively to eliminate the batch-to-batch variation from polymer-based donor or acceptor. On the other hand, the control of their active layer morphology is more challenging due to the similar chemical structure and miscibility of small-molecule donor and small-molecule accepter. Hence, this study develops a dual-additive-driven morphology optimization method for ASM-OSCs based on BTR-Cl:Y6. One solid additive – 1,4-diiodobenzene (DIB) and one liquid additive – diiodomethane (DIM) are selected, making use of their distinct interaction mechanisms with Y6 and BTR-Cl. It is found that DIB can form a eutectic phase with Y6, which can increase the intermolecular interactions and modulate the acceptor phase separation, while the simultaneous volatilization of DIM suppresses the over-aggregation of BTR-Cl during the film casting process. As a result of the synergistic morphology tuning, the optimized device delivers a power conversion efficiency (PCE) as high as 15.2%, among the highest PCE reported to date for binary ASM-OSCs without solvent annealing treatment. This work demonstrates the potential of morphology tuning via the incorporation of dual additives into ASM-OSCs, enabling them to achieve comparable efficiencies to those of conventional polymer/small-molecule based OSCs.

Two solid additives, 1-chloro-4-iodobenzene (CIB) and 1,4-dichlorobenzene (DCB), with lower melting point (mp.) of ≈52 °C, are investigated in comparison to 1,4-diiodobenzene (DIB) (mp. 131 °C). Different from DIB, the additives CIB and DCB are completely removed during spin-coating. High power-conversion efficiency of 19.1% as well as a high fill factor of 81.1% can be achieved with the in situ removable CIB as the solid additive.

Abstract

Additive engineering can precisely regulate the bulk-heterojunction active layer morphology with ideal domain size and purity, playing a critical role in development of organic solar cells (OSCs). Herein, two solid additives, 1,4-dichlorobenzene (DCB) and 1-chloro-4-iodobenzene (CIB), with low melting point (mp.) of ≈52 °C, are investigated comprehensively with comparison to 1,4-diiodobenzene (DIB, mp. 131 °C). After spin-coating, DIB residue is found in the as-cast PM6:BTP-eC9 based blend film, whereas the DCB and CIB are completely removed during the spin-coating, showing in situ removable properties that enable convenient processing. In OSCs, the DCB- and CIB-processed active layers afford power-conversion efficiencies (PCEs) of 18.2% and 18.4%, respectively, all higher than that of 17.8% for DIB. Among the three solid additives, the CIB is most effective in enhancements of absorption coefficients of the donor and acceptor, affording fast and more balanced carrier transports, and suppressing recombination. Of particular note, the CIB can provide some universality as an in situ removable solid additive, based on its elevations of PCEs for several binary and PM6:D18-Cl:L8-BO ternary active layers. Impressively, a prominent PCE of 19.1% with a remarkable fill factor of 81.1% is achieved for the CIB-processed ternary active layer. This work demonstrates the potential of in situ removable solid additive engineering in high-efficiency OSCs.

A multifunctional molecular bridging layer (3,5-bis(fluorosulfonyl)benzoic acid) is reported as a passivation layer of SnO₂ and a Li⁺ anchored layer for high efficiency, hysteresis-free and stable perovskite solar cells.

Abstract

At present, the dominating electron transport material (ETL) and hole transport material (HTL) used in the state-of-the-art perovskite solar cells (PSCs) are tin oxide and 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (Spiro-OMeTAD). However, the surface hydroxyl groups of the SnO₂ layer and the Li⁺ ions within the Spiro-OMeTAD HTL layer generally cause surface charge recombination and Li⁺ migration, significantly reducing the devices' performance and stability. Here, a molecule bridging layer of 3,5-bis(fluorosulfonyl)benzoic acid (FBA) is introduced onto the SnO₂ surface, which provides appropriate surface energy, reduces interfacial traps, forms a better energy level alignment, and, most importantly, anchors (immobilizes) Li⁺ ions in the ETL, and consequently improves the device power conversion efficiency (PCE) up to 24.26% without hysteresis. Moreover, the device with the FBA passivation layer shows excellent moisture and operational stability, maintaining over 80% of the initial PCE after 1000 h under both aging conditions. The current work provides a comprehensive understanding of the influence of the extrinsic Li⁺ ion migration within the cell on the device's performance and stability, which helps design and fabricate high-performance and hysteresis-free PSCs.

Recent progress on organic interface modifiers (OIMs) is reported according to the following categories: the anchoring groups (metal oxide, perovskite, and organic material) and frameworks (backbone and spacer). Then various strategies and effects of properly designed OIMs are discussed. Finally, an outlook on the application of extended OIM technology for the future development of efficient and stable PSCs is provided.

Abstract

Perovskite solar cells (PSCs) have demonstrated rapid progress in their power conversion efficiencies (PCEs)—from 3.8% in 2009 to 25.7% in 2022—and they have received considerable attention as a promising future photovoltaic (PV) technology. However, the operational stability of PSCs is still inadequate to satisfy the standards for commercial applications. Interface engineering has become one of the most important strategies to push PSCs’ efficiency and stability for practical use. Among the various interface engineering approaches, organic interface modifiers (OIMs) have been frequently used by the PSC field to address the issues limiting PSC stability at high efficiency levels. In this perspective, the chemical structures of state-of-the-art OIMs are discussed, and their characteristics are reviewed, as well as the impact on device performance associated with key device interfaces (e.g., metal oxide/perovskite and organic transport layer/perovskite interfaces) from a chemical and materials engineering point of view is discussed. Design considerations and the authors' perspective are discussed, on the basis of representative literature examples, for building new, customized organic OIMs to further improve PSC efficiency and stability toward commercialization.

Nature, Published online: 24 May 2023; doi:10.1038/d41586-023-01357-7

A multifunctional nitrogen-heterocyclic ring molecule is introduced for controlled vertically orientation growth of 2D passivation layer on the surface of 3D perovskite film via multi-site intermolecular interactions. With suppressed trap-states density, prolonged charge carrier lifetime, and elevated charge extraction and transfer, an optimal power conversion efficiency  of 24.6% is achieved with improved stability.

Abstract

Surface passivation via 2D perovskite is critical for perovskite solar cells (PSCs) to achieve remarkable performances, in which the applied spacer cations play an important role on structural templating. However, the random orientation of 2D perovskite always hinder the carrier transport. Herein, multiple nitrogen sites containing organic spacer molecule (1H-Pyrazole-1-carboxamidine hydrochloride, PAH) is introduced to form 2D passivation layer on the surface of formamidinium based (FAPbI₃) perovskite. Deriving from the interactions between PAH and PbI₂, the defects of FAPbI₃ perovskite are effectively passivated. Interestingly, due to the multiple-site interactions, the 2D nanosheets are found to grow perpendicularly to the substrate for promotion of charge transfer. Therefore, an impressive power conversion efficiency of 24.6% and outstanding long-term stability are achieved for the 2D/3D perovskite devices. The findings further provide a perspective in structure design of novel organic halide salts for the fabrication of efficient and stable PSCs.

Publication date: August 2023

Source: Journal of Energy Chemistry, Volume 83

Author(s): Miaoyu Lin, Jingjing He, Xinyi Liu, Qing Li, Zhanpeng Wei, Yuting Sun, Xuesong Leng, Mengjiong Chen, Zhuhui Xia, Yu Peng, Qiang Niu, Shuang Yang, Yu Hou

This Study uses a non-continuous layer of alumina nanoparticles on the surface of rough Pb:Sn perovskite films, resulting in improved conformality of the subsequent electron transport layer. This leads to the alumina nanoparticle layer acting as an interfacial buffer layer between the rough absorber and top metal electrodes and hinders unwanted direct contact between them.

Abstract

Mixed lead-tin (Pb:Sn) halide perovskites are promising absorbers with narrow-bandgaps (1.25–1.4 eV) suitable for high-efficiency all-perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat-Pb counterparts. This is partly due to the rapid crystallization of Sn-based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution-based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of V _OC, fill factor, efficiency, and stability. Herein, this study employs a non-continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron-transport layer, which is only tens of nanometres in thickness is improved. The overall maximum-power-point-tracked efficiency improves by 65% and the steady-state V _OC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 °C under full spectrum simulated solar irradiance. Aged devices show a six-fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h.

High-efficiency perovskite solar cells are tested with different hole transport materials and dopants on 175-µm sapphire under 7-MeV proton radiation. Thermal vacuum recovers the radiation-induced damage for cells free of 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as evidenced by thermal admittance spectroscopy and deep-level transient spectroscopy, making them suitable for space.

Abstract

The drastic reduction in launch and manufacturing costs of space hardware has facilitated the emergence of "commercial" space. Radiation-hard organometal halide perovskite solar cells (PSCs) with low-cost and high-efficiency potentials are promising for space applications.High-efficiency PSCs are tested with different hole transport materials (HTMs) and dopants on 175µm sapphire substrates under 7MeV-proton-irradiation-tests at accumulated fluences of 10¹¹, 10¹², and 10¹³ protons cm⁻². While all cells retain >90% of their initial power conversion efficiencies (PCEs) after 10¹¹ protons cm⁻² irradiation, PSCs that have tris(pentafluorophenyl)borane (TPFB) as the HTM dopant and poly[bis(4-phenyl)(2,5,6-trimethylphenyl) amine (PTAA) or PTAA:C8BTBT (C8BTBT = 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene) as the HTM are more tolerant to higher-fluence radiation than their counterparts with the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopant and the 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD) HTM. Radiation induces fluorine diffusion from the LiTFSI dopant toward the perovskite absorber (confirmed by depth-resolved X-ray photoelectron spectroscopy) introducing defects. Radiation-induced defects in cells with the TPFB dopant instead are different and can be “annealed out” by thermal vacuum resulting in PCE recovery. This is the first report using thermal admittance spectroscopy and deep-level transient spectroscopy for defect analyses on proton-irradiated and thermal-vacuum-recovered PSCs. The insights generated are expected to contribute to efforts in developing low-cost light-weight solar cells for space applications.

A bay-area benzamide-functionalized perylene diimide-based electron transporting layer material, namely H75 is designed and synthesized. With its excellent film-forming ability, suitable energy levels, reduced aggregation, and intrinsic high structural stability, H75-employed organic solar cells simultaneously achieve superior power conversion efficiency up to 18.26% and device stabilities under long term, thermal stress, and humidity stability testing.

Abstract

A simultaneous further increase in the power conversion efficiency (PCE) and device stability of organic solar cells (OSCs) over the current levels needs to be overcome for their commercial viability. Herein, a bay-area benzamide-functionalized perylene diimide-based electron transport layer, namely H75 is developed, to obtain the aforementioned characteristics. The advantages of H75-employed OSCs include a notable PCE up to 18.26% and outstanding device stabilities under conditions of varying severity (>95% PCE retention after 1500 h upon long-term aging and exceptional T80 lifetimes (the time required to reach 80% of initial performance) of over 1000 h in light-soaking, 500 h in thermal stress at 85 °C, 72 h in 85% high relative humidity, and 100 h in atmospheric-air conditions without encapsulation in conventional architecture). The excellent performance of H75-employed OSC can be attributed to its various beneficial features derived from the bay-area benzamide functionalities (e.g., excellent film-forming ability, suitable energy level, reduced aggregation, and intrinsic high structural stability). The findings of this work provide further insights into the molecular design of electron transport layers  for realizing more efficient and stable OSCs.

A novel surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is developed and employed as the interfacial layer between the perovskite and hole transport layer to modify the surface defect states. The TMBAI-based PSCs showed excellent stability and demonstrated power conversion efficiencies of 23.7% (0.16 cm²) and 21.7% (1 cm²) under standard AM1.5 G sunlight, respectively.

Abstract

Surface defects cause non-radiative charge recombination and reduce the photovoltaic performance of perovskite solar cells (PSCs), thus effective passivation of defects has become a crucial method for achieving efficient and stable devices. Organic ammonium halides have been widely used for perovskite surface passivation, due to their simple preparation, lattice matching with perovskite, and high defects passivation ability. Herein, a surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is employed as the interfacial layer between the spiro-OMeTAD and perovskite layer to modify the surface defect states. It is found that TMBAI treatment suppresses the nonradiative charge carrier recombination, resulting in a 60 mV increase of the open-circuit voltage (V _oc) (from 1.11 to 1.17 V) and raises the fill factor from 76.3% to 80.3%. As a result, the TMBAI-based PSCs device demonstrates a power conversion efficiency (PCE) of 23.7%. Remarkably, PSCs with an aperture area of 1 square centimeter produce a PCE of 21.7% under standard AM1.5 G sunlight. The unencapsulated TMBAI-modified device retains 92.6% and 90.1% of the initial values after 1000 and 550 h under ambient conditions (humidity 55%–65%) and one-sun continuous illumination, respectively.

Natural chlorophyll pigments named as ZnChl and H₂Chl are employed as bio-additives to optimize the morphology and molecular stack of the PM6:Y6 active layer. Owing to the fine-tuned donor–acceptor microstructure network, the photovoltaic performance of the H₂Chl bio-additive-based OSC achieves a PCE of 17.30% and the ZnChl-assisted device obtains 16.61% efficiency.

Abstract

Additive-assisted donor and acceptor domain regulation is regarded as an effective strategy to further release the potential photovoltaic performance of the existing organic solar cells (OSCs). Meanwhile, it is also critical to find high-efficient, stable, non-toxic, and low-cost biological materials as bio-additives to replace the traditional toxic halogen-based additives. In this study, bio-additives derived from a natural chlorophyll pigment named as ZnChl and H₂Chl are employed to optimize the morphology and molecular stack of the PM6:Y6 active layer. The eutectic molecular stack of the blends is more ordered and tighter after introducing the bio-additive chlorophyll derivatives to the system compared to the pristine PM6:Y6 blends. Owing to such a fine-tuned donor-acceptor microstructure network, the photovoltaic performance of the H₂Chl bio-additive-based OSC achieves a 17.30% PCE and ZnChl-based device obtains an efficiency of 16.61%, which is much higher than that of the control device with a 15.97% PCE. The result proves the feasibility of introducing environmental- and eco-friendly chlorophyll derivatives as bio-additives to further improve the photovoltaic performance of the OSCs.

A hinge-like dimer acceptor DT19 is designed and synthesized as a special third component. This dimer-doping ternary strategy exhibits excellent generality in synergistically improving device efficiency and thermal stability of relevant host systems.

Abstract

The simultaneous improvement of power conversion efficiency (PCE) and thermal stability is a critical scientific challenge in advancing the commercial applications of polymer solar cells. To address this challenge, a dumbbell-shaped dimeric acceptor, DT19, is successfully designed and synthesized. It is incorporated as a third component into the PM1:BTP-eC9 system. This ternary strategy demonstrates a synergistic enhancement of the PCE and thermal stability of the host binary system. In particular, the PM1:BTP-eC9:DT19 system maintains a PCE of over 90% even after heating at 120 °C for 200 h. Additionally, the dimer-doping ternary strategy exhibits excellent generality for the other four Y-series systems and outperforms ternary systems containing alloy-like acceptors in terms of thermal stability. It is because DT19, with its hinge-like structure, can form a semi-alloy acceptor with the host acceptor, leading to strong interchain entanglement with the polymer donor, thus overcoming phase separation and excessive aggregation under thermal stress. This new type of dimeric material, which can synergistically enhance the device efficiency and thermal stability of active layers, presents promising application prospects.