JIALINGBO

Here, the plant-derived natural green additive l-Theanine (Thea) is selected to improve the crystal quality of the perovskite absorber and obtain high-performance perovskite solar cells (PSCs) with UV/O₃ resistance. Thea significantly alleviates the perovskite phase transition and film decomposition induced by UV/O₃ treatment. This study provides exploratory research for the application of plant-derived green additives in the UV/O₃ resistance field of perovskite photovoltaics.

Abstract

As the efficiency of perovskite solar cell has skyrocketed to as high as 25.7%, their stability has become the biggest obstacle to commercialization. Preliminary analyses suggest that additive engineering may be effective in improving both solar cell efficiency and its stability. Herein, the plant-derived natural green additive of l-Theanine (Thea) is selected to improve the crystal quality of the perovskite absorber and obtain high-performance perovskite solar cells (PSCs) with ultraviolet/ozone (UV/O₃) resistance. The characterization results reveal that the CO group in Thea can effectively inhibit the precipitation of metal Pb⁰, passivate undercoordinated Pb²⁺ ions, and promote the nucleation and crystallization of perovskite. In addition, the combination of the NH group and I⁻ in the form of a hydrogen bond cooperatively reduce the probability of nonradiative recombination of photogenerated carriers and effectively improves the extraction ability of carriers from perovskite absorber. With the cooperation of CO and NH₂ groups in Thea, the champion efficiency is improved from 22.29% in the control device to 24.58%. More importantly, Thea significantly alleviates the perovskite phase transition and film decomposition induced by UV/O₃ treatment. The study provides exploratory research for the application of plant-derived green additives in the UV/O₃ resistance field of perovskite photovoltaics.

Highly efficient state-of-the-art perovskite solar cells via a “three birds with one stone” strategy are investigated. This strategy boosts power conversion efficiency and operational stability of the device.

Abstract

Suppressing nonradiative recombination in perovskite solar cells (PSCs) is crucial for increases in their power conversion efficiency and operational stability. Here, it is reported that the synchronous use of a molecule daminozide (DA), as an interlayer and additive to judiciously construct a PTAA:F4TCNQ/DA/perovskite:DA hole-selective heterojunction that diminishes thermionic losses for collecting holes at the buried interface between perovskites and PTAA:F4TCNQ, and reduces defect sites at such buried interfaces as well as in the perovskite film. The proposed “three birds with one stone” strategy significantly promotes charge transport, and both the interface carrier recombination and defect-assisted recombination are suppressed. As a result, a remarkably improved efficiency of 22.15% and an impressive fill factor of 83.92% are achieved with excellent device stability compared to 19.04% of the control device. The two values are the highest records for polycrystalline MAPbI₃-based p-i-n structural PSCs reported to date. The work provides a promising approach of three birds with one stone, employing a functional material for further improvement of PSC performance.

The combinatorial vacuum-deposition of perovskites from 4 sources is reported. More than 100 solar cells with different perovskite compositions can be prepared in a single deposition run. By fine-tuning of the deposition rates, the gradient can be altered and the best formulations in depositions with rotation can be reproduced. This approach can accelerate the development of vacuum-deposited perovskite materials and devices.

Abstract

The development of vacuum-deposited perovskite materials and devices is partially slowed down by the minor research effort in this direction, due to the high cost of the required research tools. But there is also another factor, thermal co-deposition in high vacuum involves the simultaneous sublimation of several precursors with an overall deposition rate in the range of few Å s⁻¹. This leads to a deposition time of hours with only a single set of process parameters per batch, hence to a long timeframe to optimize even a single perovskite composition. Here we report the combinatorial vacuum deposition of wide bandgap perovskites using 4 sources and a non-rotating sample holder. By using small pixel substrates, more than 100 solar cells can be produced with different perovskite absorbers in a single deposition run. The materials are characterized by spatially resolved methods, including optical, morphological, and structural techniques. By fine-tuning of the deposition rates, the gradient can be altered and the best-performing formulations in standard depositions with rotation can be reproduced. This is viewed as an approach that can serve as a basis to prototype other compositions, overcoming the current limitations of vacuum deposition as a research tool for perovskite films.

A simple small molecule 10-(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)-3,7-bis(4-vinylphenyl)-10H-phenoxazine is developed for in situ fabrication of polymer hole conductor (CL-MCz) via a facile and low-temperature cross-linking technology. The device with CL-MCz yields a champion power conversion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV.

Abstract

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) represents the state-of-the-art hole transport material (HTM) in inverted perovskite solar cells (PSCs). However, unsatisfied surface properties of PTAA and high energy disorder in the bulk film hinder the further enhancement of device performance. Herein, a simple small molecule 10-(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)-3,7-bis(4-vinylphenyl)-10H-phenoxazine (MCz-VPOZ) is strategically developed for in situ fabrication of polymer hole conductor (CL-MCz) via a facile and low-temperature cross-linking technology. The resulting polymer CL-MCz offers high energy ordering and improved electrical conductivity, as well as appropriate energy-level alignment, enabling efficient charge carrier collection in the devices. Meanwhile, CL-MCz synchronously provides satisfied surface wettability and interfacial functionalization, facilitating the formation of high-quality perovskite films with fewer bulk iodine vacancies and suppressed carrier recombination. Significantly, the device with CL-MCz yields a champion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV, which represents the highest reported efficiency for non-PTAA-based polymer HTMs in inverted PSCs. Furthermore, the corresponding unencapsulated devices exhibit competitive shelf-life stability under various operational stressors up to 2500 h, reflecting high promises of CL-MCz in the scalable PSC application. This work underscores the promising potential of the cross-linking approach in preparing low-cost, stable, and efficient polymer HTMs toward reliable PSCs.

An efficient passivator 3,4,5,6-tetrafluorophthalic acid (TFPA) is designed and applied to enhance the efficiency and stability of perovskite solar cells (PSCs). The efficiency of TFPA-modified PSCs improves to 23.70% from 21.46%. Additionally, the device without encapsulation maintains 90% of its initial efficiency after storing for 5200 h in ambient condition, whereas the control device declined beyond 30%.

Perovskite solar cells have become stars in photovoltaics due to their rapidly increased efficiency. However, their stability is still below par due to moisture permeation from grain boundaries and defects. To conquer both problems at once, a passivation agent 3,4,5,6-tetrafluorophthalicacid (TFPA) is rationally designed to heal both for not only improved cell efficiency but also better stability. It is found that the TFPA is prone to distribute along grain boundaries and has little influence within the bulk of the perovskite film. In addition, it appears that the TFPA helps to reduce the film roughness, to adjust the energy level, to facilitate hole transporting from perovskite to spiro-OMeTAD, and to increase the hydrophobicity of the perovskite film, as it is demonstrated by the inhibited nonradiative recombination and prolonged carrier lifetime. Owing to strong interactions between F, -COOH, and Pb, the device with TFPA shows outstanding efficiency and stability. A perovskite solar cell with TFPA modification delivers a champion efficiency of 23.70% and a significantly enhanced stability that the device maintains 90% of its initial efficiency after 5200 h, among the best ambient stability. Herein, an effective strategy of grain boundary passivation is provided to improve the stability of perovskite solar cells.

The texturing of crystalline silicon results in uniformly distributed pyramids. This is a key strategy to reduce the reflective losses and increase the current output of solar cells. Here, the influence of different texturing sizes is investigated on the performance and optoelectronic properties of monolithic perovskite/silicon tandems. The optimal texturing conditions to achieve devices with a certified power conversion efficiency above 28% are reported.

Abstract

Textured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high-performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high-performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.

Poly(vinylidene fluoride) (PVDF) as the polymer template used in perovksite solar cells enables slow crystal growth and efficient defect passivation, which effectively reduce non-radiation recombination and minimize E _LOSS of V _OC. PVDF-based PSCs achieve a champion efficiency of 24.21% with an excellent voltage of 1.22 V, which is the highest V _OC values reported for FAMAPb(I/Br)₃-based PSCs.

Abstract

Recently, organic–inorganic metal halide perovskite solar cells (PSCs) have achieved rapid improvement, however, the efficiencies are still behind the Shockley–Queisser theory mainly due to their high energy loss (E _LOSS) in open-circuit voltage (V _OC). Due to the polycrystalline nature of the solution-prepared perovskite films, defects at the grain boundaries as the non-radiative recombination centers greatly affect the V _OC and limit the device efficiency. Herein, poly(vinylidene fluoride) (PVDF) is introduced as polymer-templates in the perovskite film, where the fluorine atoms in the PVDF network can form strong hydrogen-bonds with organic cations and coordinate bonds with Pb²⁺. The strong interaction between PVDF and perovksite enables slow crystal growth and efficient defect passivation, which effectively reduce non-radiation recombination and minimize E _LOSS of V _OC. PVDF-based PSCs achieve a champion efficiency of 24.21% with a excellent voltage of 1.22 V, which is one of the highest V _OC values reported for FAMAPb(I/Br)₃-based PSCs. Furthermore, the strong hydrophobic fluorine atoms in PVDF endow the device with excellent humidity stability, the unencapsulated solar cell maintain the initial efficiency of >90% for 2500 h under air ambient of ≈50% humid and a consistently high V _OC of 1.20 V.

Halide perovskite photovoltaics are on the cusp of breaking into the market, but concerns remain regarding the efficiency of large-area devices, operational stability, fabrication speed, and use of toxic solvents. This review discusses various perovskite deposition methods based completely on thermal evaporation and its combination with gas reaction and solution processing to address those issues. Moreover, the authors emphasize the progress of evaporated large-area solar cells/modules and provide their perspective for attaining higher performance with evaporated perovskites.

An organic molecule 4-chloro-1,8-naphthalic anhydride (ALS) is applied to passivate the defects on the surface and grain boundary of (FAPbI₃)_0.95(MAPbBr₃)_0.05 perovskite films. ALS passivation reduces defect state density, suppresses carrier nonradiative recombination, enhances the built-in electric filed, and adjusts the band matching. The PCE of the PSC is improved from 21.52% to 23.72%, and its environmental stability is also enhanced.

Abstract

On the surface and grain boundary of perovskite films there are large quantities defects, which leads to photogenerated carrier nonradiative recombination and degrades the performance of the perovskite solar cells (PSCs). Surface passivation can suppress the detrimental effects of defect and improve the performance of PSCs. Here, an organic molecule, 4-chloro-1,8-naphthalic anhydride (ALS), is adopted to passivate the defects on the surface and grain boundary of (FAPbI₃)_0.95(MAPbBr₃)_0.05 perovskite films. The oxygen of carbonyl group in the ALS provides lone pair electron to the undercoordinated Pb²⁺ and passivated this defect. The ALS passivated perovskite films have lower trap state density and longer carrier lifetime. As a result, the photoelectric conversion efficiency (PCE) of the PSCs was improved from 21.52% to 23.72%. Furthermore, the ALS passivated PSC show good stability, and it could maintain 88% of its initial efficiency after 1200 h storage in ambient atmosphere without encapsulation.

It is requisite to develop dopant-free hole transporting materials (HTMs) to avoid formidable engineering and instability in perovskite solar cells. Organic HTMs, especially small molecules are easily reproducible. While considering the stability and efficiencies of perovskite solar cells, this review reveals the role of different molecular design strategies applied to small molecule HTMs.

Abstract

Perovskite solar cells (PSCs) have grabbed much attention of researchers owing to their quick rise in power conversion efficiency (PCE). However, long-term stability remains a hurdle in commercialization, partly due to the inclusion of necessary hygroscopic dopants in hole transporting materials, enhancing the complexity and total cost. Generally, the efforts in designing dopant-free hole transporting materials (HTMs) are devoted toward small molecule and polymeric HTMs, where small molecule based HTMs (SM-HTMs) are dominant due to their reproducibility, facile synthesis, and low cost. Still, the state-of-art dopant-free SM-HTM has not been achieved yet, mainly because of the knowledge gap between device engineering and molecular designs. From a molecular engineering perspective, this article reviews dopant-free SM-HTMs for PSCs, outlining analyses of chemical structures with promising properties toward achieving effective, low-cost, and scalable materials for devices with higher stability. Finally, an outlook of dopant-free SM-HTMs toward commercial application and insight into the development of long-term stability PSCs devices is provided.

Synergistic surface modification of mixed Sn–Pb perovskite films by the combination of piperazine and C₆₀ pyrrolidine tris-acid realizes narrow-bandgap solar cells with power conversion efficiencies up to 22.7% and substantially elongated stability.

Abstract

Interfaces in thin-film photovoltaics play a pivotal role in determining device efficiency and longevity. In this work, the top surface treatment of mixed tin–lead (≈1.26 eV) halide perovskite films for p–i–n solar cells is studied. Charge extraction is promoted by treating the perovskite surface with piperazine. This compound reacts with the organic cations at the perovskite surface, modifying the surface structure and tuning the interfacial energy level alignment. In addition, the combined treatment with C₆₀ pyrrolidine tris-acid (CPTA) reduces hysteresis and leads to efficiencies up to 22.7%, with open-circuit voltage values reaching 0.90 V, ≈92% of the radiative limit for the bandgap of this material. The modified cells also show superior stability, with unencapsulated cells retaining 96% of their initial efficiency after >2000 h of storage in N₂ and encapsulated cells retaining 90% efficiency after >450 h of storage in air. Intriguingly, CPTA preferentially binds to Sn²⁺ sites at film surface over Pb²⁺ due to the energetically favored exposure of the former, according to first-principles calculations. This work provides new insights into the surface chemistry of perovskite films in terms of their structural, electronic, and defect characteristics and this knowledge is used to fabricate state-of-the-art solar cells.

Surface treatment of inorganic perovskite film by trifluoroacetamidine featuring chelation configuration and multiple fluorine atoms allows record power conversion efficiency of inorganic perovskite solar cells.

Abstract

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI_3−x Br _x film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm² and 1.0 cm² device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.

A self-assembled monolayer composed of amphiphilic molecules as the interface layer to reduce the energy loss between the perovskite and hole transport layers is reported. A remarkable power conversion efficiency (PCE) of 20.4% for wide-bandgap perovskite solar cells is attained. Additionally, excellent performance in indoor photovoltaics and tandem solar cells, with respective PCEs of 38.7% and 23.2%, are realized.

Abstract

The applications of wide-bandgap (WBG) perovskite solar cells (PSCs) are limited by their subpar efficiency and stability due to their high density of defects, especially those at interfaces. Theoretical analyses suggest a monolayer of molecules, which is of minimum thickness and, hence, minimum resistance across the interface, possessing multifunctional groups and a permanent dipole, should effectively passivate the defects and minimize energy losses at interfaces. Herein, a self-assembled monolayer (SAM) composed of amphiphilic molecules is designed and assembled as the interface layer to reduce the energy loss and enhance interface coupling between the perovskite and hole transport layer. It is found that the SAM also builds a back surface field through a p-type doping effect, which promotes hole extraction and suppress the carrier recombination. Consequently, a remarkable power conversion efficiency (PCE) of 20.4% in parallel with a high open-circuit voltage up to 1.25 V is attained. Additionally, an indoor PCE of 38.7% is realized. Both are among the best in their respective categories. Moreover, an all-perovskite tandem solar cell is configured, presenting a decent PCE of 23.2%. This work emphasizes the significance of WBG PSCs for optoelectronic applications and indicates the eminent effects of SAMs for optimization of WBG PSCs.

Here, the plant-derived natural green additive l-Theanine (Thea) is selected to improve the crystal quality of the perovskite absorber and obtain high-performance perovskite solar cells (PSCs) with UV/O₃ resistance. Thea significantly alleviates the perovskite phase transition and film decomposition induced by UV/O₃ treatment. This study provides exploratory research for the application of plant-derived green additives in the UV/O₃ resistance field of perovskite photovoltaics.

Abstract

As the efficiency of perovskite solar cell has skyrocketed to as high as 25.7%, their stability has become the biggest obstacle to commercialization. Preliminary analyses suggest that additive engineering may be effective in improving both solar cell efficiency and its stability. Herein, the plant-derived natural green additive of l-Theanine (Thea) is selected to improve the crystal quality of the perovskite absorber and obtain high-performance perovskite solar cells (PSCs) with ultraviolet/ozone (UV/O₃) resistance. The characterization results reveal that the CO group in Thea can effectively inhibit the precipitation of metal Pb⁰, passivate undercoordinated Pb²⁺ ions, and promote the nucleation and crystallization of perovskite. In addition, the combination of the NH group and I⁻ in the form of a hydrogen bond cooperatively reduce the probability of nonradiative recombination of photogenerated carriers and effectively improves the extraction ability of carriers from perovskite absorber. With the cooperation of CO and NH₂ groups in Thea, the champion efficiency is improved from 22.29% in the control device to 24.58%. More importantly, Thea significantly alleviates the perovskite phase transition and film decomposition induced by UV/O₃ treatment. The study provides exploratory research for the application of plant-derived green additives in the UV/O₃ resistance field of perovskite photovoltaics.

Processing perovskite solar cells onto micrometer-sized pyramidal textures is a timely research topic. The potential reasons behind the various voltage losses that come along with processing perovskite thin films onto such textures are investigated in-depth via compositional, microstructural, and morphological analysis. A step-by-step guidance is presented on how to mitigate these voltage losses.

Abstract

The recent development of solution-processed perovskite thin films over micrometer-sized textured silicon bottom solar cells enables tandem solar cells with power conversion efficiencies > 30%. Next to improved light harvesting, textured silicon wafers are the industrial standard. To achieve high performance, the open-circuit voltage losses that occur when fabricating perovskite solar cells over such textures need to be mitigated. This study provides a practical guideline to discriminate and address the voltage losses at the interfaces as well as in the bulk of solution-processed double cation perovskite thin films using photoluminescence quantum yield measurements. Furthermore, the origin of these losses is investigated via morphological, microstructural, and compositional analysis and present possible mitigation strategies. The guideline will be beneficial for scientists working on randomly textured surfaces and provides a deeper understanding on this timely research topic.

A thin film of ionic salt (NaBH₄) is deposited at the PEDOT:PSS/MAPbI_3−x Cl _x interface, simultaneously achieving interfacial modification and crystallization control. The electrostatic coupling between NaBH₄ and PEDOT:PSS/perovskite results in better energy level alignment and reduced interfacial defects. A satisfactory power conversion efficiency (PCE) of 20.21% is obtained, and the long-term stability of the device is over 1000 h.

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is widely used as a hole transport layer in inverted perovskite solar cells (PSCs). However, due to the serious interface defects, imperfect energy level arrangement, and low hole transfer rate between PEDOT:PSS and perovskite, the realization of efficient and stable inverted PSCs is hindered. Herein, ionic salt sodium borohydride is used as an interfacial modifier between PEDOT:PSS and MAPbI_3−x Cl _x . NaBH₄ acts as an anchor to bond Pb²⁺ to the PEDOT:PSS surface and guides the growth of the perovskite. The champion power conversion efficiency (PCE) of the device based on NaBH₄-PEDOT:PSS reaches 20.21%, which is improved by 27.5% compared with the device based on PEDOT:PSS (15.84%). This PCE is one of the highest in inverted PSCs with PEDOT:PSS as the hole transport layer and MAPbI_3−x Cl _x as the active layer. The improved device performance is mainly attributed to the reduced valence band edge of PEDOT:PSS which matches better with the HOMO of MAPbI_3−x Cl _x , and the hole transfer rate is increased from 2.65 × 10¹⁰ to 3.69 × 10¹⁰ s⁻¹. The long-term stability of the optimized device exceeds 1000 h. This work provides a simple and effective strategy to improve the PCE and stability of inverted PSCs, which is a benefit for future popularization.

A novel multifunctional polymer, poly(methyl methacrylate-co-acrylamide), was designed and utilized to synergistically passivate the under-coordinated Pb²⁺ and anchor the I^- of the [PbI₆]⁴⁻ octahedron on the surface of a perovskite film. This passivation leads to an enhancement in the open-circuit voltage from 1.12 to 1.22 V and improved stability in solar cell devices, with the device maintaining 95 % of the initial power conversion efficiency (PCE) over 1000 h of maximum power point tracking. Additionally, a large-area solar cell device was fabricated using this approach, achieving a PCE of 20.64 %.

Abstract

Metal-cation defects and halogen-anion defects in perovskite films are critical to the efficiency and stability of perovskite solar cells (PSCs). In this work, a random polymer, poly(methyl methacrylate-co-acrylamide) (PMMA-AM), was synthesized to serve as an interfacial passivation layer for synergistically passivating the under-coordinated Pb²⁺ and anchor the I^- of the [PbI₆]⁴⁻ octahedron. Additionally, the interfacial PMMA-AM passivation layer cannot be destroyed during the hole transport layer deposition because of its low solubility in chlorobenzene. This passivation leads to an enhancement in the open-circuit voltage from 1.12 to 1.22 V and improved stability in solar cell devices, with the device maintaining 95 % of the initial power conversion efficiency (PCE) over 1000 h of maximum power point tracking. Additionally, a large-area solar cell module was fabricated using this approach, achieving a PCE of 20.64 %.

Highly efficient and stable flexible inverted perovskite solar cells are developed through modifying the interface between perovskite and hole transport layer via pentylammonium acetate molecule, which achieve a record power conversion efficiency of 23.68% (0.08 cm², certified: 23.35%) and excellent mechanical stability.

Abstract

Among the emerging photovoltaic technologies, rigid perovskite solar cells (PSCs) have made tremendous development owing to their exceptional power conversion efficiency (PCE) of up to 25.7%. However, the record PCE of flexible PSCs (≈22.4%) still lags far behind their rigid counterparts and their mechanical stabilities are also not satisfactory. Herein, through modifying the interface between perovskite and hole transport layer via pentylammonium acetate (PenAAc) molecule a highly efficient and stable flexible inverted PSC is reported. Through synthetic manipulation of anion and cation, it is shown that the PenA⁺ and Ac⁻ have strong chemical binding with both acceptor and donor defects of surface-terminating ends on perovskite films. The PenAAc-modified flexible PSCs achieve a record PCE of 23.68% (0.08 cm², certified: 23.35%) with a high open-circuit voltage (V _OC) of 1.17 V. Large-area devices (1.0 cm²) also realized an exceptional PCE of 21.52%. Moreover, the fabricated devices show excellent stability under mechanical bending, with PCE remaining above 91% of the original PCE even after 5000 bends.

An oxime acid-based additive (EHA) is adopted as a multidentate-coordinate agent in perovskite solar cells. Benefitting from the crystallization modulation and defect passivation effect, a simultaneous enhancement in photovoltaic performance and device stability is attained in the EHA-modified perovskite solar cells.

Abstract

Crystal growth regulation has become an effective solution to reduce the defects at grain boundaries (GBs) and surfaces of perovskite films for better photovoltaic performances. Oxime acid materials are maturely used as selective collectors in the flotation separation of oxide minerals. Such materials, showing a strong coordination effect and high selectivity with lead, may have great potential in controlling the crystal growth and passivating the defect of perovskite film, which are rarely applied in perovskite solar cells (PerSCs). Herein, an oxime acid-based material with multi-coordination sites, ethyl 2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetate (EHA), is incorporated into the PbI₂ precursor solution to fabricate high-performance PerSCs using a two-step method. The multidentate coordination effect of EHA can link and integrate the PbI₂ colloidal clusters to achieve pre-aggregation in the PbI₂ precursor solution, facilitating the sequent crystal growth progress of perovskite film. Meanwhile, EHA can connect grains and fill GBs, which is favorable for charge transfer and passivating both Pb-I anti-site and iodine vacancy defects. As a result, the optimal devices show an enhanced efficiency of 24.1% and excellent humidity and thermal stability. This work affords a promising strategy to fabricate efficient and stable PerSCs via multidentate coordination-induced crystallization control and GB passivation.

A thin layer of low-dimensional halide (LDH) is inserted at the perovskite/C₆₀ interface in inverted (positive-intrinsic-negative) perovskite solar cells. Induced by imidazolium-based ionic liquid, the LDH enables a strong electronic coupling at the heterointerface to effectively shift the surface gap states out of the perovskite bandgap. This approach enables >24% efficiency along with excellent thermal and operational stability.

Abstract

The photovoltaic performance of inverted (positive-intrinsic-negative) perovskite solar cells (PSCs) is predominantly limited by interfacial recombination loss. Here, by constructing a low-dimensional halide/perovskite heterostructure, non-radiative recombination pathways at the perovskite/C₆₀ contact are effectively eliminated and a voltage loss of only 370 mV is achieved in inverted PSCs. Through molecular engineering of the organic spacer, a strong electronic coupling is enabled at the heterointerface, which effectively shifts the gap states out of the bandgap and leads to a prolonged carrier lifetime of 4.28 µs. Our strategy enables a power conversion efficiency of 24.09% (certified 23.54%) for inverted PSCs with an open-circuit voltage of 1204 mV, and an efficiency of 21.89% (certified 21.48%) for centimeter-scale cells. The devices retain 92% of the initial efficiency after 85 °C thermal aging for over 1400 h, and 95% of the initial efficiency after 1008 h of maximum power point operation under AM1.5G illumination in air.

A new polyfullerene material (PFBS-C12) is developed that can work efficiently as the electron transporting material of p-i-n perovskite solar cells (PSCs). PFBS-C12 retains the figure-of-merits of conventional fullerene molecules, and shows suppressed aggregation and more conformal coverage on perovskites compared to PCBM. As a result, the p-i-n PSCs based on PFBS-C12 realize a high efficiency of 23.2 % with good device stability.

Abstract

Electron transporting materials (ETMs) play vital roles in determining the efficiency and stability of inverted perovskite solar cells. The widely used PCBM is prone to undesirable aggregation and migration in a cell, thus impairing device stability. In this work, we develop a new type of ETMs by polymerizing C60 fullerene with an aromantic linker unit. The resultant polyfullerene (PFBS-C12) not only maintains the good optoelectronic properties of fullerenes, but also can address the aforementioned aggregation problem of PCBM. The polyfullerene-based blade-coated cells exhibit a high efficiency of 23.2 % and good device stability that maintain 96 % of initial efficiency after >1300-hour light soaking. An aperture efficiency of 18.9 % is also achieved on a 53.6-cm² perovskite mini-module. This work provides a new strategy for designing ETMs that retain the key figure-of-merits of conventional fullerene molecules and enable more stable perovskite solar devices simultaneously.

A strong interaction between the relatively soft Sn²⁺, compared to Sn⁴⁺, and the soft sulfur in thiourea, associated with hard and soft acid and base theory, suppresses effectively a disproportionation reaction of 2Sn²⁺→ Sn⁴⁺ + Sn⁰, which results in a substantial enhancement of carrier lifetime and consequently photovoltaic performance of Sn-Pb alloyed perovskite solar cell.

Abstract

Regulation of Lewis acid-base adduct intermediate is more critical for the dual metal ions of Sn²⁺ and Pb²⁺ than for the single metal ion such as Pb²⁺ in preparing high quality perovskite films. It has been reported here that the photovoltaic performance of Sn-Pb alloyed perovskite solar cells is dependent on the interaction between metal ions and Lewis base additives. Urea and thiourea are selected as an O- and a S-donor, respectively, which is used as an additive in the precursor solution including equimolar SnI₂ and PbI₂ together with organic iodides of formamidinium iodide and methylammonium iodide, forming a nominal composition of FA_0.5MA_0.5Pb_0.5Sn_0.5I₃. Open-circuit voltage (V _oc) is increased while maintaining short-circuit photocurrent density (J _sc) after the addition of urea. On the other hand, both J _sc and V _oc are simultaneously increased by adding thiourea, leading to a considerable increase in power conversion efficiency from 14.58% (control) to 18.59%. A strong interaction between the relatively soft Sn²⁺, compared to Sn⁴⁺, and the soft sulfur in thiourea, associated with hard and soft acid and base theory, suppresses effectively a disproportionation reaction of 2Sn²⁺→ Sn⁴⁺ + Sn⁰, which results in a substantial enhancement of carrier lifetime and consequently photovoltaic performance.

Commercialization of all-perovskite tandem solar cells requires both, a thermally stable narrow-bandgap perovskite and a tunnel junction. Here all-FA Pb-Sn perovskite with superior intrinsic thermal stability and metal-oxide-based tunnel junction are deployed synchronously, which resulted in a power conversion efficiency of 26.3% and much improved thermal stability in all-perovskite tandem solar cells.

Abstract

Commercialization of all-perovskite tandem solar cells requires thermally stable narrow-bandgap (NBG) perovskites and tunnel junction. However, the high content of methylammonium (MA) and organic hole transport layer used in NBG perovskite subcell undermine the thermal stability of all-perovskite tandems. Here, thermally stable mixed lead-tin NBG perovskite solar cells (PSCs) are developed by using only formamidinium (FA) for the A-site cation. Solution-processed indium tin oxide nanocrystals (ITO NCs) are deployed further to replace the conventional organic charge transport layer. Meanwhile, the ITO NCs layer simultaneously functions as a recombination layer in the tunnel junction, which simplifies the architecture of all-perovskite tandem devices. The thermally stable all-FA Pb-Sn PSCs achieve a high power conversion efficiency (PCE) of 21.0%. With the thermally stable all-FA NBG perovskite and optimized tunnel junction, a stabilized PCE of 26.3% is further obtained in all-perovskite tandems. The unencapsulated tandem devices maintain >90% of their initial efficiencies after 212 h aging at 85 °C in the N₂ atmosphere. The strategies herein offer a crucial step toward efficient and thermally stable all-perovskite tandem solar cells.

The role of the surface modulator cannot simply be attributed to the passivation effect. Here, it is shown that the strong-interaction surface modulator, 2-thiopheneethylammonium iodide (2-TEAI, is helpful in inverted (p-i-n) perovskite solar cells. Through forming a quasi-2D structure and reconfiguring the electronic energy level of perovskite film, 2-TEAI contributes to the reduced interfacial recombination losses, and enhanced device performance.

Abstract

Successful manipulation of halide perovskite surfaces is typically achieved via the interactions between modulators and perovskites. Herein, it is demonstrated that a strong-interaction surface modulator is beneficial to reduce interfacial recombination losses in inverted (p-i-n) perovskite solar cells (IPSCs). Two organic ammonium salts are investigated, consisting of 4-hydroxyphenethylammonium iodide and 2-thiopheneethylammonium iodide (2-TEAI). Without thermal annealing, these two modulators can recover the photoluminescence quantum yield of the neat perovskite film in contact with fullerene electron transport layer (ETL). Compared to the hydroxyl-functionalized phenethylammonium moiety, the thienylammonium facilitates the formation of a quasi-2D structure onto the perovskite. Density functional theory and quasi-Fermi level splitting calculations reveal that the 2-TEAI has a stronger interaction with the perovskite surface, contributing to more suppressed non-radiative recombination at the perovskite/ETL interface and improved open-circuit voltage (V _OC) of the fabricated IPSCs. As a result, the V _OC increases from 1.11 to 1.20 V (based on a perovskite bandgap of 1.63 eV), yielding a power conversion efficiency (PCE) from ≈20% to 21.9% (stabilized PCE of 21.3%, the highest reported PCEs for IPSCs employing poly[N,N′′-bis(4-butylphenyl)-N,N′′-bis(phenyl)benzidine] as the hole transport layer, alongside the enhanced operational and shelf-life stability for unencapsulated devices.

Accurate measurement of the power conversion efficiencies of perovskite-containing multijunction solar cells is more complicated than for a single-junction cell. Measurement conditions for accurate performance testing of perovskite-containing multijunctions, including perovskite-Si and all-perovskite tandems are discussed. Common errors and pitfalls that sometimes mislead the interpretation of the results and recommendations for evaluating the accuracy of the data are presented.

Perovskite multijunctions (PVSK MJs) have made remarkable progress with monolithic PVSK/PVSK tandems surpassing the efficiency of single-junction (1 J) PVSK cells and PVSK/Si cells reported to exceed the 30% efficiency mark. These efficiencies are reported at standard test conditions (STC), established by the photovoltaic (PV) community to facilitate comparison between devices and technologies. Herein, it is discussed why an accurate STC performance measurement for a MJ is more complicated than for a 1 J cell and the special aspects to be considered when measuring the current–voltage characteristics and the performance of PVSK-containing MJ cells are emphasized. It is discussed why a spectrally adjustable solar simulator is needed and the sequence of accurate performance measurement, namely measurement of the spectral response of each junction, adjustment of the spectrum, and appropriate protocols for measuring the power output of the device at STC, is presented. For all these, common errors and pitfalls that sometime lead to misleading interpretation of the results are presented, and the methods to evaluate the accuracy of the data when a spectrally adjustable solar simulator is not available are recommended. Finally, first step is taken toward recommending performance measurement approaches when high throughput is required as will eventually be in a production line.