Ligang Yuan

Additive and passivator strategy is applied to fabricate wide-bandgap perovskite solar cells with bandgap of 1.68 eV. KSCN is introduced as additive and TEABr is used to passivate perovskite/C₆₀ interface, achieving a open-circuit voltage of 1.22 V. This leads to a power conversion efficiency of 22.02% for the champion device, which is one of the highest efficiencies at this bandgap.

Wide-bandgap (WBG) perovskite solar cells (PSCs) play a crucial role in tandem devices. However, the severe nonradiative recombination that occurs at the interface between perovskite and electron transport layer (ETL) leads to excessive open-circuit voltage (V _OC) loss, which hinders the further improvement of the photovoltaic conversion efficiency (PCE). To mitigate the V _OC loss in WBG PSCs, the defects in grains and grain boundaries are reduced as well as the energy-level alignment between perovskite layer and ETL, so as to improve the carrier collection efficiency, is optimized. Herein, potassium thiocyanate is introduced as an additive and 2-thiophenethylammonium bromide (TEABr) is used to passivate perovskite/C₆₀ interface. The synergistic treatment reduces the defect density and prolongs the carrier lifetime, implying that nonradiative recombination is effectively suppressed. Meanwhile, the energy-level alignment of the perovskite and C₆₀ is optimized, leading to the improvement of V _OC. Finally, WBG PSCs with a bandgap of 1.68 eV achieve a V _OC of 1.22 V (with a V _OC loss of 0.46 V) and a PCE of 22.02%.

In this paper, the passivation of perovskite solar cells without Pb²⁺ defects was passivated through a reasonable molecular design. First, the passivation molecules CDT-N and CDT-S were designed and synthesized. Then, the passivation effect of passivation molecules on defects and the improvement effect on device efficiency and stability were studied. Finally, a perspective on future trends of passivation strategies is provided.

Abstract

The uncoordinated lead cations are ubiquitous in perovskite films and severely affect the efficiency and stability of perovskite solar cells (PSCs). In this work, 15-crown-5 with various heteroatoms are connected to the organic semiconductor carbazole diphenylamine, and two new compounds, CDT-S and CDT-N, are developed to modify the Pb²⁺ defects in perovskite films through the anti-solvent method. Apart from the oxygen atoms, there are also N atoms on crown ether ring in CDT-N, and both S and N heteroatoms in CDT-S. The heteroatoms enhance the interaction between the crown ether-based semiconductors and the undercoordinated Pb²⁺ defect in perovskite. Particularly, the stronger interaction between S atoms and Pb²⁺ further enhances the defect passivation effect of CDT-S than CDT-N, thereby more effectively suppressing the non-radiative recombination of charge carriers. Finally, the efficiency of the device treated with CDT-S is up to 23.05 %. Moreover, the unencapsulated device based on CDT-S maintained 90.5 % of the initial efficiency after being stored under dark conditions for 1000 hours, demonstrating good long-term stability. Our work demonstrates that crown ethers are promising in perovskite solar cells, and the crown ether containing multiple heteroatoms could effectively improve both efficiency and stability of devices.

Strain regulation and nonradiative recombination suppression by 2D ligands in Pb/Sn-based narrow-bandgap perovskite solar cells (PSCs) are comprehensively understood. It is found that the mixture of electroneutral cation with long alkyl chain and iodate with short alkyl chain balances the tensile strain throughout perovskite film, which contributes to minimizing the energy losses from bulk and interfaces in PSCs.

Abstract

Mixed lead and tin (Pb/Sn) hybrid perovskites exhibit a great potential in fabricating all-perovskite tandem devices due to their easily tunable bandgaps. However, the energy deficit and instability in Pb/Sn perovskite solar cells (PSCs) constrain their practical applications, which renders defect passivation engineering indispensable to develop highly efficient and long-term stable PSCs. Herein, the mechanisms of strain tailoring and defect passivation in Pb/Sn PSCs by 2D ligands are investigated. The 2D ligands include electroneutral cations with long alkyl chain (LAC), iodates with relatively short alkyl chain (SAC) and their mixtures. This study reveals that LAC ligands facilitate the relaxation of tensile strain in perovskite films while SAC ligands cause strain buildup. By mixing LAC/SAC ligands, tensile strain in perovskite films can be balanced which improves solar cell performance. PSCs with admixed β-guanidinopropionic acid (GUA)/phenethylammonium iodide (PEAI) exhibit enhanced open circuit voltage and fill factor, which is attributed to reduced nonradiative recombination losses in the bulk and at the interfaces. Furthermore, the operational stability of PSCs is slightly improved by the mixed 2D ligands. This work reveals the mechanisms of 2D ligands in strain tailoring and defect passivation toward efficient and stable narrow-bandgap PSCs.

Nature Photonics, Published online: 08 December 2022; doi:10.1038/s41566-022-01111-x

Publication date: 15 February 2023

Source: Chemical Engineering Journal, Volume 454, Part 4

Author(s): Han Sol Yang, Eui Hyun Suh, Sung Hoon Noh, Jaemin Jung, Jong Gyu Oh, Kyeong Ho Lee, Dongwoon Lee, Jaeyoung Jang

The surface regulation of 3D perovskite through dipolar 4-trifluoromethylbenzamidine hydrochloride (TFPhFACl) molecule results in an impressive efficiency of 24.0%. The formation of dipolar layer not only accelerates the hole transporting from 3D perovskite to spiro-MeOTAD, but also suppresses the nonradiative recombination through the coordination of TFPhFA⁺ cations with Pb–I octahedron.

Abstract

Mixed 2D/3D perovskite solar cells (PSCs) show promising performances in efficiency and long-term stability. The functional groups terminated on a large organic molecule used to construct 2D capping layer play a key role in the chemical interaction mechanism and thus influence the device performance. In this study, 4-(trifluoromethyl) benzamidine hydrochloride (TFPhFACl) is adopted to construct 2D capping layer atop 3D perovskite. It is found that there are two mechanisms synergistically contributing to the increase of efficiency: 1) The TFPhFA⁺ cations form a dipole layer promoting the interfacial charge transport. 2) The suppressed nonradiative recombination of perovskite through the coordination of TFPhFA⁺ cations with Pb–I octahedron, as well as the recrystallization of 3D perovskite induced by Cl^- ions. As a result, the PSC delivers an efficiency of 24.0% with improved open-circuit voltage (V _OC) of 1.16 V, short-circuit current density (J _SC) of 25.42 mA cm^-2, and fill factor of 81.26%. The device shows no decrease in efficiency after 1500 h stored in the air indicating the good stability. The utilization of TFPhFACl not only provides a facile way to optimize the interfacial problems, but also gives a new perspective for rational design of large spacer molecule for constructing efficient 2D/3D PSCs.

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.

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.

The structural ordering of 2D organic–inorganic hybrid perovskite results in the structural ordering of the 2D/3D perovskite heterostructure and further boosts the excellent optoelectronic properties of the heterostructure films.

Abstract

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA_0.8Cs_0.2PbI₃, we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕμ), and carrier diffusion length (L _D) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of ≈1.3 μs, high ϕμ of ≈18.56 cm² V⁻¹ s⁻¹, and long L _D of ≈7.85 μm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA₂PbI₄. This carrier diffusion length is comparable to that of some perovskite single crystals (>5 μm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.

The processing environment of perovskite solar cells in pure inert gas significantly increases the practical production cost. The thermal annealing atmosphere of quasi-2D perovskite films can affect the self-assembly behavior of bulky organic cations, which modulates the phase distribution of 2D species with different n values. Air annealing modulates the crystallization process, resulting in high-quality quasi-2D perovskite films.

Although the photovoltaic performance of perovskite solar cells (PSCs) has reached commercial standards, the processing environment of a purely inert gas atmosphere significantly increases the cost of installing manufacturing facilities in actual manufacturing plants and hinders their commercial mass production. The thermal annealing condition of quasi-2D perovskite films can significantly affect the self-assembly behavior of bulky organic cations, which modulates the phase distribution of 2D species with different n values. Herein, the properties of quasi-2D perovskite annealing in a N₂ versus an environment representative of industrial conditions, i.e., open-air with 30% humidity are compared. It is found that the crystallization process of perovskites is regulated by air annealing, leading to high-quality 2D perovskite films with reduced trap density, well-aligned phase distribution, and released residual strain. The resulting devices prepared by air annealing achieve a power conversion efficiency of 18% with high reproducibility and suppressed voltage loss. The enhanced thermal stability of the air-annealed films is proved by in situ grazing incidence wide-angle X-ray scattering. The combination of air annealing and simple planar structures would facilitate the mass production of PSCs.

Indium zinc oxide is used for the interfacial layer to minimize ohmic resistance as well as the transparent conducting oxide in the semitransparent solar cell. The wide-bandgap (1.71 eV) perovskite solar cell delivers an efficiency to 19.26%, and a four-terminal perovskite/CdTe tandem solar cell and two-terminal perovskite/silicon tandem solar cell achieve efficiencies of 22.59% and 26.34%.

To overcome the efficiency limit of perovskite single-junction solar cells, it is vital to develop various types of tandem solar cells. Especially, wide-bandgap (WBG) perovskite solar cells (PSCs) have played an important role in high-efficiency tandem solar cells. Herein, an indium zinc oxide-based interfacial structure is developed to improve the performance of a WBG PSC and used as the transparent electrode for semitransparent (ST) PSCs. This approach minimizes ohmic contact between the electron-transport layer and metallic electrode, which also accelerates electron transfer and suppresses trap-assisted carrier recombination. As a result, the WBG PSC (1.71 eV) shows the best power conversion efficiency of 19.26% and improves operational stability. When the optimized ST-PSC is used as the ST-top cell, perovskite/CdTe four-terminal and perovskite/silicon (double-side polished) two-terminal tandem solar cells achieve a maximum efficiency of 22.59% and 26.34%, respectively.

Nature Communications, Published online: 02 December 2022; doi:10.1038/s41467-022-35218-0

Nature Communications, Published online: 02 December 2022; doi:10.1038/s41467-022-35092-w

In this study, the use of non-toxic and low-cost vitamins such as α-tocopherol is highlighted to achieve high-quality CsPbX₃ perovskite nanocrystals (PNCs) with enhanced optical performance. This combination facilitates the chemical formulation to prepare highly emissive and long-term stable 3D printed polymer/PNCs composites processable by additive manufacturing, showing a high potentiality for scalable and robust optoelectronics.

Abstract

The use of non-toxic and low-cost vitamins like α-tocopherol (α-TCP, vitamin E) to improve the photophysical properties and stability of perovskite nanocrystals (PNCs), through post-synthetic ligand surface passivation, is demonstrated for the first time. Especially interesting is its effect on CsPbI₃ the most unstable inorganic PNC. Adding α-TCP produces that the photoluminescence quantum yield (PLQY) of freshly prepared and aged PNCs achieves values of ≈98% and 100%, respectively. After storing 2 months under ambient air and 60% relative humidity, PLQY is maintained at 85% and 67%, respectively. α-TCP restores the PL features of aged CsPbI₃ PNCs, and mediates the radiative recombination channels by reducing surface defects. In addition, the combination of α-TCP and PNCs facilitates the chemical formulation to prepare PNCs-acrylic polymer composites processable by additive manufacturing. This enables the development of complex shaped parts with improved luminescent features and long-term stability for 4 months, which is not possible for non-modified PNCs. A PLQY ≈92% is reached in the 3D printed polymer/PNC composite, the highest value obtained for a red-emitting composite solid until now as far as it is known. The passivation shell provided by α-TCP makes that PNCs inks do not suffer any degradation process avoiding the contact with the environment and preserve their properties after reacting with polar monomers during composite polymerization.

A synergistic effect of surface p-doping and passivation on the inorganic perovskite CsPbIBr₂ is studied. The p-type doping treatment optimizes film quality, improves energy level alignment, and suppresses nonradiative recombination. Finally, the device achieves a high PCE of 11.02%, a V _oc of 1.33 V, and a FF of 0.75. Lead leakage is well reduced within the safe range of human blood lead content.

Abstract

Wide-bandgap inorganic cesium lead halide CsPbIBr₂ is a popular optoelectronic material that researchers are interested in because of the character that balances the power conversion efficiency and stability of solar cells. It also has great potential in semitransparent solar cells, indoor photovoltaics, and as a subcell for tandem solar cells. Although CsPbIBr₂-based devices have achieved good performance, the open-circuit voltage (V _oc) of CsPbIBr₂-based perovskite solar cells (PSCs) is still lower, and it is critical to further reduce large energy losses (E _loss). Herein, a strategy is proposed for achieving surface p-type doping for CsPbIBr₂-based perovskite for the first time, using 1,5-Diaminopentane dihydroiodide at the perovskite surface to improve hole extraction efficiency. Meanwhile, the adjusted energy levels reduce E _loss and improve V _oc of the CsPbIBr₂ PSCs. Furthermore, the Cs- and Br-vacancies at the interface are filled, reducing structural disorder and defect states and thus improving the quality of the perovskite film. As a result, the target device achieves a high efficiency of 11.02% with a V _oc of 1.33 V, which is among the best values. In addition to the improved performance, the stability of the target device under various conditions is enhanced, and the lead leakage is effectively suppressed.

A room-temperature molten salt dimethylamine acetate is developed as the solvent for precursor solutions, which also regulates the phase conversion process of the CsPbI₃ film. Consequently, 1.25 V of the open-circuit voltage and >21% power conversion efficiency are achieved, which is the record highest for CsPbI₃ perovskite solar cells reported so far.

Abstract

All-inorganic CsPbI₃ perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI₃ solar cells is mainly subject to a large open-circuit voltage (V _OC) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI₃ film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI₃ structure and eliminate the Cs₄PbI₆ intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac)₃ is formed, which finally affords high-quality CsPbI₃ films. With this approach, the charge capture activity of defects in the CsPbI₃ film is significantly suppressed. Consequently, a V _OC of 1.25 V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.

Three novel self-doped molecules named t-PyDIN, t-PyDINO and t-PyDINBr are developed as cathode interfacial materials for OSCs. The devices based on t-PyDINBr and t-PyDINO exhibit PCEs of 17.24 % and 17.56 %, respectively. Notably, the device based on t-PyDIN even reached a PCE of 18.25 %, which is improved by 51.3 % compared with that of the device without a cathode interfacial layer. This result is among the best efficiencies reported to date.

Abstract

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

Fast synthesis of α-phase crystallized mixed-cation perovskite powder assisted with moisture in ambient air is developed. The significant role of moisture in introducing the solvation effect and the facet orientation change of PbI₂ is demonstrated by a combined experimental and theoretical investigation. Perovskite solar cells based on α-phase mixed-cation perovskite powder deliver an impressive PCE of 24.07 %.

Abstract

Phase-pure crystallised perovskite is considered an excellent precursor for fabricating high-stability perovskite films with minimal defects. However, currently available protocols for synthesising crystallised perovskites must be conducted in an inert atmosphere or in the presence of an organic solvent as the reaction medium, which hinders mass production. Here, we report the fast synthesis of α-phase-crystallised perovskite powder assisted by moisture in ambient air. Moisture can promote the reaction between PbI₂ and organic salts and facilitate complete phase transition, as demonstrated in a joint experimental and theoretical study. Perovskite solar cells with a power conversion efficiency of 24.07 % were achieved using phase-pure crystallised perovskite powder as the precursor. This ambient-air-compatible method opens new vistas to reproducible high-quality precursors for large-scale photovoltaic applications.

Publication date: 1 January 2023

Source: Chemical Engineering Journal, Volume 451, Part 3

Author(s): Kai-Chi Hsiao, Yen-Fu Yu, Ching-Mei Ho, Meng-Huan Jao, Yu-Hsiang Chang, Shih-Hsuan Chen, Yin-Hsuan Chang, Wei-Fang Su, Kun-Mu Lee, Ming-Chung Wu

A hole transport material (BDT-DPA-F) is designed, and it can assemble into a fibril network, showing an obviously improved hole mobility, a decreased energy disorder and high scalability. The perovskite solar cells based on BDT-DPA-F without any dopant obtain promising power conversion efficiencies of 23.12 % (certified 22.48 %) for small-area devices (0.062 cm²) and 20.17 % for large-area modules (15.64 cm²).

Abstract

Dopant-free organic hole transport materials (HTMs) remain highly desirable for stable and efficient n-i-p perovskite solar cells (pero-SCs) but rarely succeed. Here, we propose a molecular assembly strategy to overcome the limited optoelectronic properties of organic HTMs by precisely designing a linear organic small molecule BDT-DPA-F from the atomic to the molecular levels. BDT-DPA-F can assemble into a fibril network, showing an obviously improved hole mobility and decreased energy disorder. The resultant pero-SCs showed a promising efficiency of 23.12 % (certified 22.48 %), which is the highest certified value of pero-SCs with dopant-free HTMs, to date. These devices also showed a weak-dependence of efficiency on size, enabling a state-of-the-art efficiency of 22.50 % for 1-cm² device and 20.17 % for 15.64-cm² module. For the first time, the pero-SCs based on dopant-free HTMs realized ultralong stabilities with T ₈₀ lifetimes over 1200 h under operation or thermal aging at 85 °C.

An effective molecular engineering is demonstrated to simultaneously improve the performance and stability of perovskite devices. This strategy allows to obtain desired optoelectronic and chemical properties for novel nonspiro-based hole conductors, which leads to the fabrication of solar cells displaying remarkable efficiency of 21.2% with excellent stability under the harsh aging conditions.

Abstract

Despite considerable development in performance, both poor operational stability and high costs associated with hole conductors such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) and Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) of perovskite solar cells (PSCs) need to be addressed by the research community. Here, two nonspiro hole transporting materials (HTMs), namely HTM-1 and HTM-2, are designed and straightforwardly synthesized exhibiting remarkable electrochemical properties and hole mobilities. In particular, the PSC based on the methoxy derivative (HTM-2) exhibits a remarkable efficiency of 21.2% (stabilized efficiency of 20.8%), which is superior to the benchmark HTM spiro-OMeTAD (stabilized efficiency of 20.4%). These results establish that the molecular design is effective in improving the performance of PSCs. Importantly, these two HTMs show admissible long-term stability under different harsh conditions such as thermal stress up to 85 °C, high humidity level of 60% ± 10%, and continuous illumination over 1000 h. These insights allow correlating the impact of molecular design on optoelectronic properties of nonspiro-based hole conductors with the overall device performance.

A systematic understanding of the mechanism of photon propagation and carrier kinetics of semitransparent perovskite solar cells (ST-PSCs) is critical for the development of high-performance ST-PSCs. In this paper, the key factors affecting the high light utilization of ST-PSCs are deeply discussed from the theoretical analysis, and the recent advances from the view of photon propagation management and carrier kinetics regulation of ST-PSCs are summarized, which provides guidance for promoting the rapid development and further commercialization of ST-PSCs.

Abstract

Semitransparent perovskite solar cells (ST-PSCs) are ideal candidates for building-integrated photovoltaics (BIPV) and tandem solar cells (TSCs) owing to their tunable bandgap and high visible transparency. The best power conversion efficiency (PCE) of ST-PSCs is close to 15% with an average visible transmittance of over 20%, which still lags far behind the PCE of normal opaque PSCs. This can be attributed to the poor light utilization efficiency (LUE) of ST-PSCs. Herein, the pivotal routes for maximizing LUE of ST-PSCs in terms of photon propagation management and carrier kinetics regulation are systematically rationalized. First, the fundamental theoretical analyses on optical processes and electronic properties are provided. Then, insights on photon propagation management measures and carrier kinetics regulation strategies are provided. Furthermore, a summary of the promising commercial application of ST-PSCs in BIPV and TSCs is provided. Finally, the main progress of ST-PSCs is briefly summarized, and the directions for the commercialization of ST-PSCs are proposed.