JIANG ZHI XUAN

A new mechanism to understand the role of organic ammonium salt (OAS) in improving performances of perovskite solar cells is proposed. Besides passivating defects by itself, OAS also augments the passivation effect of excess PbI₂ on the surface of the perovskite film by dispersing it into a discontinuous layer. Furthermore, using PbI₂ nanosheets fully dispersed in advance boosts the efficiency to 23.14 %.

Abstract

Organic ammonium salts (OASs) have been widely used to passivate perovskite defects. The passivation mechanism is usually attributed to coordination of OASs with unpaired lead or halide ions, yet ignoring their interaction with excess PbI₂ on the perovskite film. Herein, we demonstrate that OASs not only passivate defects by themselves, but also redistribute excess aggregated PbI₂ into a discontinuous layer, augmenting its passivation effect. Moreover, alkyl OAS is more powerful to disperse PbI₂ than a F-containing one, leading to better passivation and device efficiency because F atoms restrict the intercalation of OAS into PbI₂ layers. Inspired by this mechanism, exfoliated PbI₂ nanosheets are adopted to provide better dispersity of PbI₂, further boosting the efficiency to 23.14 %. Our finding offers a distinctive understanding of the role of OASs in reducing perovskite defects, and a route to choosing an OAS passivator by considering substitution effects rather than by trial and error.

Perovskite solar cells (PSCs) have demonstrated enormous potential as next generation of photovoltaic technologies. Herein, the latest advances of interfacial materials for highly efficient and stable PSCs are summarized with organized classification. The theory and multifaceted roles of interface engineering are analyzed and insights on the deposition strategy of interlayers and outlook of interface engineering for PSCs toward commercialization are provided.

Abstract

Organic–inorganic lead halide perovskite solar cells (PSCs) have demonstrated enormous potential as a new generation of solar-based renewable energy. Although their power conversion efficiency (PCE) has been boosted to a spectacular record value, the long-term stability of efficient PSCs is still the dominating concern that hinders their commercialization. Notably, interface engineering has been identified as a valid strategy with extraordinary achievements for enhancing both efficiency and stability of PSCs. Herein, the latest research advances of interface engineering for various interfaces are summarized, and the basic theory and multifaceted roles of interface engineering for optimizing device properties are analyzed. As a highlight, the authors provide their insights on the deposition strategy of interlayers, application of first-principle calculation, and challenges and solutions of interface engineering for PSCs with high efficiency and stability toward future commercialization.

An ionic liquid (IL) is designed to passivate undercoordinated Pb²⁺ by chemically bonding to form an IL capped perovskite surface, leading to superior photovoltaic performance and operational stability. Specifically, the small solar cell (0.1 cm²) exhibits an open-circuit voltage of 1.192 V, power conversion efficiency of 24.33%, and the large area (10.75 cm²) integrated module achieves a PCE of 20.33%.

Abstract

Metal-halide perovskite has emerged as an effective photovoltaic material for its high power conversion efficiency (PCE), low cost and straightforward fabrication techniques. Unfortunately, its long-term operational durability, mainly affected by halide ion migration and undercoordinated Pb²⁺ is still the bottleneck for its large-scale commercialization. In this work, an ionic liquid (IL) is designed to effectively cap the grain surface for improved stability and reduced trap density. More specifically, the Br⁻ in the IL passivates the undercoordinated Pb²⁺ by chemically bonding to it, resulting in a thin layer of ionic-liquid-perovskite formed on the surface, leading to improved photovoltaic performance and better stability. Specifically, the solar cell exhibits an open-circuit voltage of 1.192 V and PCE of 24.33% under one-sun illumination with negligible hysteresis, and a large area (10.75 cm²) integrated module achieves PCE of 20.33%. Moreover, the bare device maintains over 90% of its initial efficiency after 700 h of aging at 65 °C. It also shows outstanding stability with only about 10% degradation after being exposed to the ambient environment for 1000 h. The superior efficiency and stability demonstrate that the present IL passivating strategy is a promising approach for high-performance large area perovskite solar cell applications.

Single-crystal solar cells with high efficiency and a superior weak light response are achieved by engineering the hole extraction interface. Remarkably enhanced efficiency of 22.1% under AM 1.5G irradiation and indoor efficiency of 39.2% under 1000 lux irradiation are obtained, which are both the highest values for MAPbI₃ single-crystal solar cells.

Abstract

Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer-thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open-circuit voltage (V _OC) and energy loss. Herein, hydrophobic poly(3-hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb²⁺ and promote ion diffusion in a confined space, resulting in higher-quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V _OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI₃ single-crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single-crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.

Heating colloidal tin oxide solutions changes the particle size distribution from bimodal to unimodal. This mitigates agglomerates, resulting in uniform, compact, and gap-free SnO₂ electron transport layers. Processing perovskite layers on top results in films with reduced grain boundaries and fewer defects, along with improved perovskite/SnO₂ interfaces. This facile process results in significantly enhanced perovskite solar cell performance.

Tin dioxide is a frequently reported electron transporting material for perovskite solar cells (PSCs) that yields high-performance devices and can be solution processed from aqueous colloidal solutions. While being very simple to process, electron transport layers deposited in this manner often lead to nonuniform film morphology, significantly affecting the morphology of the subsequent perovskite layer, lowering the overall device performance. Herein, it is shown that heating the SnO₂ colloidal solution (70 °C) results in compact SnO₂ films with increased surface coverage and fewer gaps in the SnO₂ film. Such films possess threefold higher lateral electrical conductivity than those obtained from room-temperature solutions. The narrow gaps in the SnO₂ film also reduce the chances of direct contact between the indium tin oxide electrode and the perovskite layer, yielding better contact with less voltage loss. The improved SnO₂ surface coverage induces larger perovskite grains (≈565 nm) than those prepared from the room-temperature solution (≈273 nm). Finally, using these compact SnO₂ layers, efficient and stable PSCs that retain ≈85% of the initial power conversion efficiency of 20.67% after 100 h of maximum power point tracking are demonstrated.

Nature Energy, Published online: 16 December 2021; doi:10.1038/s41560-021-00953-z

A hydrophobic ammonium salt, 4-(trifluoromethyl) benzylamine, is introduced to form a quasi-2D hybrid perovskite by a one-step spin-coating method. Due to the relatively low surface energy of fluorinated molecules, an upper gradient low-dimensional structure is formed spontaneously from top to bottom, and more stable devices are obtained with a power conversion efficiency of 17.07%.

Abstract

Highly efficient and stable quasi-2D hybrid perovskite solar cells (PSCs) using hydrophobic 4-(trifluoromethyl) benzylamine (4TFBZA) as the spacer cation are successfully demonstrated. It is found that the incorporation of hydrophobic 4TFBZA into MAPbI₃ can effectively induce a spontaneous upper gradient 2D (SUG-2D) structure, passivate the trap states, and restrain the ion motion. Meanwhile, the strong hydrogen bonding of F···HN between 4TFBZA ions and methylamine ions can effectively suppress the decomposition of perovskite, which gives the device a better thermal stability. Besides, due to the SUG-2D structure with hydrophobic 4TFBZA, the device also exhibits a better moisture stability. The SUG-2D-structure-based device exhibits a power conversion efficiency of 17.07% with a high open-circuit voltage of 1.10 V and a notable fill factor of 71%. This work provides a new strategy for constructing efficient and stable quasi-2D PSCs, and it is an inspiration for the packaging strategy of perovskites.

Ethylenediamine (EDA) coating changes the p-type tin-lead perovskite to n-type, increases the built-in potential, and decreases the open-circuit voltage (V _oc) loss in perovskite solar cells. With Br inclusion into the lattice and passivation by EDA, the highest power conversion efficiency of 21.74% and Voc of 0.86 V is achieved using Cs_0.025FA_0.475MA_0.5Sn_0.5Pb_0.5I_2.975Br_0.025 perovskite film with a bandgap of 1.25 eV.

Abstract

Tin-lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open-circuit voltage (V _oc) loss. Here, it is revealed that the p-type surface of perovskite transforms to n-type, based on post-treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi-energy level at the surface of the perovskite layer, and increases the built-in potential from 0.56 to 0.76 V, which increases the V _oc by more than 100 mV. It is demonstrated that EDA can lower the defect density (Sn⁴⁺ amount) by screening perovskite against oxygen, and by bonding with undercoordinated Sn on the surface. This study further explores the role of Br anion inclusion in the perovskite lattice from the viewpoint of reducing the lattice strain and Urbach energy. Finally, a high V _oc of 0.86 V is obtained, corresponding to a voltage deficit of 0.39 V, using a perovskite absorber with a bandgap of 1.25 eV and the highest PCE (21.74%) reported so far for Sn-Pb PSCs is achieved.

The catastrophic failure of n-i-p type perovskite solar cells under operation is reported, which is proven by the corrosion of the metal electrode on the edge. After inserting a thin MoO₃, the improved Ag thin film morphology as well as better energy alignment suppress the catastrophic failure of perovskite solar cells.

Abstract

The n-i-p type perovskite solar cells suffer unpredictable catastrophic failure under operation, which is a barrier for their commercialization. The fluorescence enhancement at Ag electrode edge and performance recovery after cutting the Ag electrode edge off prove that the shunting position is mainly located at the edge of device. Surface morphology and elemental analyses prove the corrosion of the Ag electrode and the diffusion of Ag⁺ ions on the edge for aged cells. Moreover, much condensed and larger Ag clusters are formed on the MoO₃ layer. Such a contrast is also observed while comparing the central and the edge of the Ag/Spiro-OMeTAD film. Hence, the catastrophic failure mechanism can be concluded as photon-induced decomposition of the perovskite film and release reactive iodide species, which diffuse and react with the loose Ag clusters on the edge of the cell. The corrosion of the Ag electrode and the migration of Ag⁺ ions into Spiro-OMeTAD and perovskite films lead to the forming of conducting filament that shunts the cell. The more condensed Ag cluster on the MoO₃ surface as well as the blocking of holes within the Spiro-OMeTAD/MoO₃ interface successfully prevent the oxidation of Ag electrode and suppress the catastrophic failure.

Aiming at improving the performance of tin perovskite solar cells, this study analyzes the Sn²⁺ oxidation process in the precursor solution and proposes a source-regulating strategy to prepare high-quality perovskite films with low Sn⁴⁺ defect densities. A device with high certified efficiency and excellent long-term stability is obtained.

Abstract

Tin-based halide perovskites have attracted great attention in the perovskite solar cells (PSCs) community with their suitable band gaps, excellent optoelectronic properties, and non-toxicity. However, because of their poor chemical stability, it is challenging to fabricate highly stable and efficient tin PSCs (TPSCs). In this study, the origin of the Sn²⁺ oxidation ahead of film formation is concentrated on, and it is found that the ionization of SnI₂ in precursor plays a decisive role. Accordingly, SnI₂ dissociation and the subsequent Sn²⁺ oxidation can be restricted in precursor by employing reductive complexes as additives. This dual-functional source-regulating strategy effectively helps prepare high-quality perovskite films with low Sn⁴⁺ defect densities. As a result, the unencapsulated TPSCs show a considerable power-conversion efficiency of 10.03% (certified 9.38%) and maintain 90% of its initial efficiency after 1000 h of light aging testing.

An effective strategy to simultaneously obtain high photocurrent and fill factor in tandem organic solar cells is presented. By increasing the proportion of the non-fullerene acceptor with strong absorption in the front sub-cell, maximum photocurrent can be obtained without significantly increasing the thickness of the front sub-cell, thus ensuring a high fill factor and high photocurrent in device, with a power conversion efficiency over 18%.

Abstract

The maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub-cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub-cell in such TOSCs can be reduced by increasing the proportion of a non-fullerene acceptor in the active layer. The non-fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub-cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub-cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine-turning of the composition in the front sub-cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained.

Nature Materials, Published online: 10 June 2021; doi:10.1038/s41563-021-01029-9

Dipole–dipole interaction induced self-assembly of phenoxazine-based hole-transporting material, N01, is achieved by introducing a hexyl bromide side-chain to tune its self-assembling properties. N01 exhibits a higher intrinsic hole mobility and more favorable interfacial properties for hole transport, extraction and perovskite growth, with a conversion efficiency of 21.85 % to be realized in an inverted PSC.

Abstract

Delicately designed dopant-free hole-transporting materials (HTMs) with ordered structure have become one of the major strategies to achieve high-performance perovskite solar cells (PSCs). In this work, we report two donor-π linker-donor (D-π-D) HTMs, N01 and N02, which consist of facilely synthesized 4,8-di(n-hexyloxy)-benzo[1,2-b:4,5-b′]dithiophene as a π linker, with 10-bromohexyl-10H-phenoxazine and 10-hexyl-10H-phenoxazine as donors, respectively. The N01 molecules form a two-dimensional conjugated network governed by C−H⋅⋅⋅O and C−H⋅⋅⋅Br interaction between phenoxazine donors, and synchronously construct a three-dimension lamellar structure with the aid of interlaminar π–π interaction. Consequently, N01 as a dopant-free small-molecule HTM exhibits a higher intrinsic hole mobility and more favorable interfacial properties for hole transport, hole extraction and perovskite growth, enabling an inverted PSC to achieve a very impressive power conversion efficiency of 21.85 %.

A novel, rapid, and scalable treatment method that significantly improves perovskite thin film crystallinity is introduced. Treated perovskite solar cells (PSCs) exhibit enhanced efficiencies, increased stabilities, and improved reproducibility. Versatility and universality are demonstrated using: CH₃NH₃PbI₃ (MAPbI₃) PSCs with thicknesses from 500–1300 nm; large-area (>1 cm²) devices; a range of device architectures and compositions including Cs_0.1FA_0.9Pb(I_0.95Br_0.05) devices.

Abstract

Metal-halide perovskite solar cells (PSCs) have had a transformative impact on the renewable energy landscape since they were first demonstrated just over a decade ago. Outstanding improvements in performance have been demonstrated through structural, compositional, and morphological control of devices, with commercialization now being a reality. Here the authors present an aerosol assisted solvent treatment as a universal method to obtain performance and stability enhancements in PSCs, demonstrating their methodology as a convenient, scalable, and reproducible post-deposition treatment for PSCs. Their results identify improvements in crystallinity and grain size, accompanied by a narrowing in grain size distribution as the underlying physical changes that drive reductions of electronic and ionic defects. These changes lead to prolonged charge-carrier lifetimes and ultimately increased device efficiencies. The versatility of the process is demonstrated for PSCs with thick (>1 µm) active layers, large-areas (>1 cm²) and a variety of device architectures and active layer compositions. This simple post-deposition process is widely transferable across the field of perovskites, thereby improving the future design principles of these materials to develop large-area, stable, and efficient PSCs.

A bifunctional SnO₂ colloid is developed using small molecular oxalate. The resultant SnO₂ films show “no annealing effect”, contributing to stabilized PCEs of 22.40% and 22.37% for high temperature process (HTP) SnO₂ planar and mesoporous PSCs, respectively. The high stability of HTP SnO₂ PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO₂.

Abstract

SnO₂ compact layer (c-SnO₂) frequently suffers from degradation in high temperature processes (HTP) such as crack, worse interfacial contact, and electrical properties, that is, annealing effect. To solve this problem, a kind of bifunctional SnO₂ colloid is developed by using small molecular oxalate whose organic components can be removed clearly at a low temperature process (LTP). The c-SnO₂ and SnO₂ mesoporous layer (m-SnO₂) derived from the fresh and aged sols with the same colloid show no annealing effect, decreasing oxygen vacancy, and adsorbing water on increasing annealing temperature. The champion devices of LTP and HTP SnO₂ planar perovskite solar cells (PSCs) achieve, respectively, stabilized photoelectric conversion efficiencies (PCEs) of 20.74% and 20.70%. In contrast, the performance of champion devices of their mesoporous counterparts is significantly improved, showing nearly hysteresis free character with stabilized PCEs of 22.40% and 22.37%, respectively. The inclusion of m-SnO₂ plays a role of an energy bridge, improving electrons collection efficiency, which is supported by photoluminescence and transient photoluminescence characterizations. HTP SnO₂ mesoporous PSCs can preserve 97.6% and 80% of their initial PCEs after aging for 25 weeks and 8-h irradiated/16-h dark cycle within 104 h. The high stability of HTP SnO₂ PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO₂.

Stabilizing high-efficiency perovskite solar cells (PSCs) at operating conditions remains an unresolved issue hampering its large-scale commercial deployment. Here, we report a star-shaped polymer to improve charge transport and inhibit ion migration at the perovskite interface. The incorporation of multiple chemical anchor sites in the star-shaped polymer branches strongly controls the crystallization of perovskite film with lower trap density and higher carrier mobility and thus inhibits the nonradiative recombination and reduces the charge-transport loss. Consequently, the modified inverted PSCs show an optimal power conversion efficiency of 22.1% and a very high fill factor (FF) of 0.862, corresponding to 95.4% of the Shockley-Queisser limited FF (0.904) of PSCs with a 1.59-eV bandgap. The modified devices exhibit excellent long-term operational and thermal stability at the maximum power point for 1000 hours at 45°C under continuous one-sun illumination without any significant loss of efficiency.

This work presents a comprehensive review on the current understanding, and apparent contradictions, of experimental observation, interpretation, and theoretical hypotheses presented in the state-of-the-art mixed dimensional 2D-3D perovskite literature and identifies promising future research directions for enhancing the stability and performance of such devices.

Abstract

Perovskite solar cells are a potential game changer for the photovoltaics industry, courtesy of their facile fabrication and high efficiency. Despite this, commercialization is being held back by poor stability. To become economically feasible for commercial production, perovskite solar cells must meet or exceed industry standards for operational lifetime and reliability. In this regard, mixed dimensional 2D-3D perovskite solar cells, incorporating long carbon-chain organic spacer cations, have shown promising results, with enhancement in both device efficiency and stability. Dimensional engineering of perovskite films requires a delicate balance of 2D and 3D perovskite composition to take advantage of the specific properties of each material phase. This review summarizes and assesses the current understanding, and apparent contradictions in the state-of-the-art mixed dimensional perovskite solar cell literature regarding the origin of stability and performance enhancement. By combining and comparing results from experimental and theoretical studies it is focused on how the perovskite composition, film formation methods, additive and solvent engineering influence efficiency and stability, and identify future research directions to further improve both key performance metrics.

Polyaromatic passivator 4-hydroxybiphenyl substituted naphthalene-1,8-dicarboximide provides chemical passivation (protonic/Lewis-base groups system) and energetic passivation (creating benign midgap states) effects. The Lewis-base/polyaromatic conjugation/protonic system reduces defects efficiently and avoids superoxide anions in perovskite solar cells.

Abstract

As game-changers in the photovoltaic community, perovskite solar cells are making unprecedented progress while still facing grand challenges such as improving lifetime without impairing efficiency. Herein, two structurally alike polyaromatic molecules based on naphthalene-1,8-dicarboximide (NMI) and perylene-3,4-dicarboximide (PMI) with different molecular dipoles are applied to tackle this issue. Contrasting the electronically pull–pull cyanide-substituted PMI (9CN-PMI) with only Lewis-base groups, the push–pull 4-hydroxybiphenyl-substituted NMI (4OH-NMI) with both protonic and Lewis-base groups can provide better chemical passivation for both shallow- and deep-level defects. Moreover, combined theoretical and experimental studies show that the 4OH-NMI can bind more firmly with perovskite and the polyaromatic backbones create benign midgap states in the excited perovskite to suppress the damage by superoxide anions (energetic passivation). The polar and protonic nature of 4OH-NMI facilitates band alignment and regulates the viscosity of the precursor solution for thicker perovskite films with better morphology. Consequently, the 4OH-NMI-passivated perovskite films exhibit reduced grain boundaries and nearly three-times lower defect density, boosting the device efficiency to 23.7%. A more effective design of the passivator for perovskites with multi-passivation mechanisms is provided in this study.

Perovskites with formamidinium-dominated components have revolutionized photovoltaics owing to their suitable bandgap and excellent carrier transport properties. By tunning the crystal structure stability, mitigating defect state and protecting the perovskite from complex environments, high-performance and long-term operational stable photovoltaics can be achieved. The efficient and targeted tactics for these goals are summarized and examined, providing great insight for future reaserch.

Abstract

Organic–inorganic hybrid perovskite materials have attracted widespread attention in the photovoltaic field. The best-certified perovskite single-junction photovoltaics have achieved an impressive power conversion efficiency of 25.5%. Particularly, formamidinium lead triiodide (FAPbI₃) perovskite material has been considered to be one of the most promising materials for fabricating highly efficient single-junction solar cells due to its suitable bandgap (1.43 eV). However, the metastable α-FAPbI₃ perovskite phase, which can spontaneously transform into the undesirable δ phase, limits their further applications. Accordingly, stabilizing the α phase and achieving high-quality films are keys for achieving high-efficiency and long-term operational perovskite photovoltaics. In this review, strategies for stabilization of α-FAPbI₃ are discussed in detail, and the corresponding thermodynamic mechanisms are also summarized. Moreover, the methods to eliminate defects and improve carrier transport are thoroughly reviewed, which is important for achieving high-performance photovoltaic devices with outstanding long-term operational stability. Finally, possible the future research directions of FAPbI₃ photovoltaics toward commercialization are discussed.

A universality strain-regulation approach—crosslinking-enabled strain-regulating crystallization (CSRC)—is introduced to eliminate intrinsic tensile strain in perovskite film, which significantly boosts the perovskite solar cells’ (PSCs) stability and performance. The CSRC approach precisely modulates the perovskite film strain through synchronous cooperation of perovskite crystallization manipulation and in situ chemical crosslinking process, as showcased with several types of crosslinking agents.

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Abstract

α-Formamidinium lead triiodide (α-FAPbI₃) represents the state-of-the-art for perovskite solar cells (PSCs) but experiences intrinsic thermally induced tensile strain due to a higher phase-converting temperature, which is a critical instability factor. An in situ crosslinking-enabled strain-regulating crystallization (CSRC) method with trimethylolpropane triacrylate (TMTA) is introduced to precisely regulate the top section of perovskite film where the largest lattice distortion occurs. In CSRC, crosslinking provides in situ perovskite thermal-expansion confinement and strain regulation during the annealing crystallization process, which is proven to be much more effective than the conventional strain-compensation (post-treatment) method. Moreover, CSRC with TMTA successfully achieves multifunctionality simultaneously: the regulation of tensile strain, perovskite defects passivation with an enhanced open-circuit voltage (V _OC = 50 mV), and enlarged perovskite grain size. The CSRC approach gives significantly enhanced power conversion efficiency (PCE) of 22.39% in α-FAPbI₃-based PSC versus 20.29% in the control case. More importantly, the control PSCs’ instability factor—residual tensile strain—is regulated into compression strain in the CSRC perovskite film through TMTA crosslinking, resulting in not only the best PCE but also outstanding device stability in both long-term storage (over 4000 h with 95% of initial PCE) and light soaking (1248 h with 80% of initial PCE) conditions.

The concept of a ternary-cation two-step sequential deposition method by incorporating cesium acetate (CsAc) into a lead iodide precursor is put forward, which generates cesium lead iodide (CsPbI₃) crystal nuclei. When an organic amine salts solution spin coats the substate, the acetate moves upward and induces perovskite orientational and uniform crystallization achieving fewer defects and higher photovoltaic efficiency.

Abstract

State-of-the-art, high-performance formamidinium-lead-iodide-based (FAPbI₃-based) perovskite photovoltaics are mainly prepared by one-step antisolvent dripping deposition or two-step sequential fabrication methods. Compared with the one-step deposition, the two-step fabricated perovskite films tend to grow columnar perovskite grains vertically which is easier for carrier extraction and transportation. Herein, the concept of formamidinium methylammonium cesium based ternary-cation two-step sequential deposition method is put forward by incorporating cesium acetate (CsAc) into a lead iodide precursor, which generates CsPbI₃ crystal nuclei improving the further perovskite crystallization. When the formamidinium/methylammonium-based organic amine salts solution is spin coated on the PbI₂ substrate, the acetate moves upward and induces perovskite orientational and uniform crystallization, which can go a step further for the vertical columnar grains achieving fewer defects and higher photovoltaic efficiency. The champion outdoor power conversion efficiency of the modified device under AM 1.5G reaches 21.50% and its indoor efficiency at 1000 lux reaches 40.99%. This work paves the way for further exploring ternary-cation two-step sequential deposition methods to prepare high-performance perovskite photovoltaics.

Additive-induced synergies of defect passivation and energetic modification in perovskite solar cells are investigated, which boost power conversion efficiency and stability of the devices.

Abstract

Defect passivation via additive and energetic modification via interface engineering are two effective strategies for achieving high-performance perovskite solar cells (PSCs). Here, the synergies of pentafluorophenyl acrylate when used as additive, in which it not only passivates surface defect states but also simultaneously modifies the energetics at the perovskite/Spiro-OMeTAD interface to promote charge transport, are shown. The additive-induced synergy effect significantly suppresses both defect-assisted recombination and interface carrier recombination, resulting in a device efficiency of 22.42% and an open-circuit voltage of 1.193 V with excellent device stability. The two photovoltaic parameters are among the highest values for polycrystalline CsFormamidinium/Methylammonium (FAMA)/FAMA based n-i-p structural PSCs using low-cost silver electrodes reported to date. The findings provide a promising approach by choosing the dual functional additive to enhance efficiency and stability of PSCs.

Regarding the bottlenecks of defect density and ion migration at grain boundary within mixed halide perovskites, the profound superiorities brought by pyridinic nitrogen-doped graphdiyne (N-GDY) are systematically highlighted. It is proposed that the spatial confinement coupling with the electrostatic repulsion effect, induced by the intrinsic 2D structure of N-GDY, contributes to the conclusive capability of impeding the halide ion migration.

Abstract

The solution processing in hybrid perovskite films inevitably results in the formation of detrimental defects at grain boundaries (GBs) that deteriorate the optoelectronic properties and bring about severe hysteresis as well as operational instability. Here, an effective scenario to alleviate the imperfection issue at perovskite GBs via incorporating pyridinic nitrogen-doped graphdiyne (N-GDY) is proposed. Taking full advantage of periodic acetylenic linkages and introduced pyridinic N atoms, the deep-level trap states like Pb–I antisite defects and under-coordinated Pb atoms are considerably passivated, thus diminishing the undesired non-radiative recombination. Additionally, the spatial confinement coupling with electrostatic repulsion effect originated from the intrinsic 2D structure of N-GDY, has been identified to deal with the halide ion migration behavior. Such contributions are further theoretically evidenced with the charge density delocalization as well as the ion migration energy barrier elevation. The authors unprecedentedly verified the superiorities based on the flexible chemical-tailorability of atomic crystal GDY materials toward polycrystalline perovskite related energy conversion devices.

This work presents a comprehensive review on the current understanding, and apparent contradictions, of experimental observation, interpretation, and theoretical hypotheses presented in the state-of-the-art mixed dimensional 2D-3D perovskite literature and identifies promising future research directions for enhancing the stability and performance of such devices.

Abstract

Perovskite solar cells are a potential game changer for the photovoltaics industry, courtesy of their facile fabrication and high efficiency. Despite this, commercialization is being held back by poor stability. To become economically feasible for commercial production, perovskite solar cells must meet or exceed industry standards for operational lifetime and reliability. In this regard, mixed dimensional 2D-3D perovskite solar cells, incorporating long carbon-chain organic spacer cations, have shown promising results, with enhancement in both device efficiency and stability. Dimensional engineering of perovskite films requires a delicate balance of 2D and 3D perovskite composition to take advantage of the specific properties of each material phase. This review summarizes and assesses the current understanding, and apparent contradictions in the state-of-the-art mixed dimensional perovskite solar cell literature regarding the origin of stability and performance enhancement. By combining and comparing results from experimental and theoretical studies it is focused on how the perovskite composition, film formation methods, additive and solvent engineering influence efficiency and stability, and identify future research directions to further improve both key performance metrics.

The significant advances in efficient photoabsorbent materials have been instrumental in the performance enhancement of semitransparent organic solar cells (ST‐OSCs) from <7% to 12–14% (with good visible transmittance) only in the last 3 years. This study reviews the progress of photoabsorbent materials for ST‐OSCs, and discusses the structure–property relationships and future perspectives for the development of multifunctional ST‐OSCs.

Abstract

Semi‐transparent organic solar cells (ST‐OSCs) have revolutionized the field of photovoltaics (PVs) due to their unique abilities, such as transparency and color tunability, and have transformed normal power‐harvesting OSC devices into multifunctional devices, such as building‐integrated photovoltaics, agrivoltaics, floating photovoltaics, and wearable electronics. Very recently, ST‐OSCs have seen remarkable progress, with a rapid increase in power conversion efficiency from below 7% to 12–14%, with an average visible transparency of 9–25%, especially due to the use of low bandgap semiconductors including polymer donors and non‐fullerene acceptors that exhibit absorption in the near‐infrared region as photoabsorbent materials. From this perspective, the latest developments in ST‐OSCs stemming from the innovations in photovoltaic materials that delivered multifunctional ST‐OSCs with top‐of‐the‐line power conversion efficiencies are discussed to shed light on the structure‐property relationship between molecular design and current challenges in this cutting‐edge research field. Finally, personal perspectives, including research directions for the future use of ST‐OSCs in multifunctional applications, are also proposed.

Nature Reviews Materials, Published online: 23 March 2021; doi:10.1038/s41578-021-00286-z