Chen Weijie

Publication date: 15 March 2023

Source: Joule, Volume 7, Issue 3

Author(s): Tinghuan Yang, Chuang Ma, Weilun Cai, Shiqiang Wang, Yin Wu, Jiangshan Feng, Nan Wu, Haojin Li, Wenliang Huang, Zicheng Ding, Lili Gao, Shengzhong (Frank) Liu, Kui Zhao

The ordered arrangement of methylamine dipoles is induced by the polar molecule to form a top-down macroscopic polarization of the film. Reorientation of dipoles contributes to forming a gradient energy band and changes the surrounding dielectric environment, facilitating efficient separation and directional transport of carriers. The photoelectric conversion efficiency and stability of the perovskite solar cells are significantly improved.

Abstract

Despite great progress in perovskite photovoltaics, it should be noted that the intrinsic disorder dipolar cations in organic–inorganic hybrid perovskites exert negative effects on the energy band structure as well as the carrier separation and transfer dynamics. However, oriented polarization achieved by applying an external electric field may cause irreversible damage to perovskites. Herein, a unique and efficient strategy is developed to modulate the intrinsic dipole arrangement in perovskite films for high-performance and stable perovskite solar cells (PSCs). The spontaneous reorientation of dipolar cation methylamine is triggered by a polar molecule, constructing a vertical polarization during crystallization regulation. The oriented dipole determines a gradient energy-level arrangement in PSCs and more favorable energetics at interfaces, effectively enhancing the built-in electric field and suppressing the nonradiative recombination. Besides, the dipole reorientation induces a local dielectric environment to remarkably reduce exciton binding energy, leading to an ultralong carrier diffusion length of up to 1708 nm. Accordingly, the n–i–p PSCs achieve a significant increase in power conversion efficiency, reaching 24.63% with negligible hysteresis and exhibiting outstanding stabilities. This strategy also provides a facile route to eliminate the mismatched energetics and enhance carrier dynamics for other novel photovoltaic devices.

Pseudo-bilayer heterojunction (PBHJ) strategy realizes high-performance binary organic solar cells (OSCs) with high fill factor in PM6:Y6 and PTQ10:Y6 systems. The donor concentration in the PBHJ active layer is only 4 mg mL⁻¹, demonstrating the excellent potential for poorly soluble donors and acceptors in future OSCs applications.

Forming proper film morphology in organic solar cells (OSCs) is important to govern the exciton dissociation and charge transport. Herein, high-performance pseudo-bilayer heterojunction (PBHJ) OSCs with donor:acceptor (D:A) bilayer architecture are reported by sequentially depositing two layers of diluted active solution with different D:A ratios. Such pseudo-bilayer films can not only enable the cascaded components distributed in the vertical direction, but also afford large donor and acceptor (D/A) interfaces for efficient exciton dissociation. Additionally, the D:A active layer on the bottom substrate can act as a seed to promote the crystallization process of the upper film during the sequential casting process. The PBHJ strategy on two representative D:A blends, PM6:Y6 and PTQ10:Y6, is implemented. Benefiting from the synergetic effects of efficient exciton dissociation and balanced charge transport, the devices based on PM6:Y6 and PTQ10:Y6 show high power conversion efficiencies of 17.73% and 17.81%, respectively. Notably, the presented PBHJ devices are fabricated by using dilute chloroform solution (4 mg mL⁻¹ for donor), demonstrating the excellent potential for poorly soluble donors and acceptors in future OSCs applications.

A green anti-solvent deposition method that allows precise control of crystallization and phase transition in wide-bandgap perovskite is reported. It can regulate the lead iodide (PbI₂) adduct to directly form α-perovskite, and effectively reduces nonradiative recombination in the bulk. Finally, a remarkable open-circuit voltage (V _OC) of 1.255 V and an optimal efficiency of 20.06% is achieved.

Abstract

Wide-bandgap perovskite solar cells (PSCs) have attracted a lot of attention due to their application in tandem solar cells. However, the open-circuit voltage (V _OC) of wide-bandgap PSCs is dramatically limited by high defect density existing at the interface and bulk of the perovskite film. Here, an anti-solvent optimized adduct to control perovskite crystallization strategy that reduces nonradiative recombination and minimizes V _OC deficit is proposed. Specifically, an organic solvent with similar dipole moment, isopropanol (IPA) is added into ethyl acetate (EA) anti-solvent, which is beneficial to form PbI₂ adducts with better crystalline orientation and direct formation of α-phase perovskite. As a result, EA-IPA (7-1) based 1.67 eV PSCs deliver a power conversion efficiency of 20.06% and a V _OC of 1.255 V, which is one of the remarkable values for wide-bandgap around 1.67 eV. The findings provide an effective strategy for controlling crystallization to reduce defect density in PSCs.

A novel 3D-shaped perylene diimide derivative is developed and utilized as a guest electron acceptor to construct ternary organic solar cells. A promising power conversion efficieny of 18.29% in the ternary device is recorded with concurrently enhanced V _oc of 0.849 V, J _sc of 27.55 mA cm⁻², and fill factor of 78.21%.

Abstract

Integrating a third component into the binary system is considered to be one of the most effective strategies to further enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Here, a novel perylene diimide (PDI) derivative featuring 3D structure, TPA-4PDI, with tetraphenyladamantane central core is developed as a guest electron acceptor to be incorporated into the PM6:Y6 binary system. The champion PCE of ternary OSC is recorded to be 18.29% by adding 7.5 wt.% of TPA-4PDI in the ternary blend, which photovoltaic performance is enhanced with synergistically increased open-circuit voltage (V _oc) of 0.849 V, short-circuit current density (J _sc) of 27.55 mA cm⁻², and fill factor (FF) of 78.21%. TPA-4PDI exhibits a complementary absorption band with PM6 and Y6 while its lowest unoccupied molecular orbital (LUMO) energy level falls between the two host materials. The addition of TPA-4PDI can effectively suppress the recombination behavior, inhibit the excessive aggregation of Y6 and improve the morphology of PM6:Y6 blend. All these effects function synergistically and then lead to the enhancement of V _oc, J _sc, and FF in ternary OSCs. This study suggests that developing PDI derivatives as the third component is an effective method to further improve the performance of ternary OSCs.

A cross-linkable biological molecule α-lipoic acid is first employed to construct self-healable polymer network in buried interface and perovskite layer via dynamic covalent disulfide bonds and intermolecular hydrogen bonds. The passivation and toughening effects endow perovskite films with excellent mechanical stability and self-healing capacity. The resultant bending-degraded flexible devices can recover to 95% of its original efficiency under mild condition.

Abstract

Halide perovskites are qualified to meet the flexibility demands of optoelectronic field because of their merits of flexibility, lightness, and low cost. However, the intrinsic defects and deformation-induced ductile fracture in both perovskite and buried interface significantly restrict the photoelectric performance and longevity of flexible perovskite solar cells (PVSCs). Here, a dual-dynamic cross-linking network is schemed to boost the photovoltaic efficiency and mechanical stability of flexible PVSCs by incorporating natural polymerizable small molecule α-lipoic acid (LA). The LA therein can be autonomously ring-opening polymerized through dynamic disulfide bonds and hydrogen bonds, concurrently forming coordination bonds to interact with perovskite component. Importantly, the polymerization product can serve as efficacious passivating and toughening agents to simultaneously optimize interfacial contact, enhance perovskite crystallinity and sustain robust mechanical bendability. Subsequently, the rigid (or flexible) p-i-n device realizes a champion efficiency of 22.43% (or 19.03%) with prominent operational stability. Moreover, the dual-dynamic cross-linking network endows PVSCs with bendability and self-healing capacity, allowing the optimized devices to retain >80% efficiency after 3000 bending cycles, and subsequently restore to ≈95% of its initial efficiency under mild heat-treatment. This toughening and self-healing strategy provides a facile and efficient path to prolong operational lifetime of flexible device.

Two polymerized small molecular acceptors (namely PZC16 and PZC17) based on a new CH-series small molecule acceptor are reported. Non-aromatic linkers (ethynyl for PZC16 and vinylene for PZC17) are adopted and their effect on the photo-physical properties as well as the device performance is systematically investigated. A champion power conversion efficiency of 16.33% is achieved by the PM6:PZC17-based devices.

Abstract

Developing new polymerized small molecular acceptor (PSMA) is pivotal for improving the performance of all-polymer solar cells. On the basis of this newly developed CH-series small molecule acceptors, two PSMAs are reported herein (namely PZC16 and PZC17, respectively). To reduce the molecular torsion caused by the traditional aromatic π-bridges, non-aromatic conjugated units (ethynyl for PZC16 and vinylene for PZC17) are adopted as the linkers and their effect on the photo-physical properties as well as the device performance are systematically investigated. Both polymer acceptors exhibit co-planar molecular conformation, along with broad absorption ranges and suitable energy levels. In comparison with the PM6:PZC16 film, the PM6:PZC17 film exhibits more uniform phase separation in morphology with a distinct bi-continuous network and better crystallinity. The PM6:PZC17-binary-based devices exhibit a satisfactory PCE of 16.33%, significantly higher than 9.22% of the PZC16-based devices. Impressively, PM6:PZC17-based large area device (ca. 1 cm²) achieves an excellent PCE of 15.14%, which is among the top performance for reported all-polymer solar cells (all-PSCs).

A new passivation strategy is proposed to improve the optoelectronic properties of the zinc oxide (ZnO) electron-transport layer by incorporating stable organic open-shell donor-acceptor type diradicaloids. The passivation efficiency is found related to the electronic push-pull effect of the diradicaloids, which can be designed by tailoring the terminal donor segments.

Abstract

The zinc oxide (ZnO) nanoparticles (NPs) are well-documented as an excellent electron transport layer (ETL) in optoelectronic devices. However, the intrinsic surface flaw of the ZnO NPs can easily result in serious surface recombination of carriers. Exploring effective passivation methods of ZnO NPs is essential to maximize the device's performance. Herein, a hybrid strategy is explored for the first time to improve the quality of ZnO ETL by incorporating stable organic open-shell donor-acceptor type diradicaloids. The high electron-donating feature of the diradical molecules can efficiently passivate the deep-level trap states and improve the conductivity of ZnO NP film. The unique advantage of the radical strategy is that its passivation effectiveness is highly correlated with the electron-donating ability of radical molecules, which can be precisely controlled by the rational design of molecular chemical structures. The well-passivated ZnO ETL is applied in lead sulfide (PbS) colloidal quantum dot solar cells, delivering a power conversion efficiency of 13.54%. More importantly, as a proof-of-concept study, this work will inspire the exploration of general strategies using radical molecules to construct high-efficiency solution-processed optoelectronic devices.

Imidazolium-based zwitterionic ionic liquid 1-(1-ethyl-3-imidazolium)propane-3-sulfonate (EIMS) is studied as additive to enhance the performance of the FAPbI₃ perovskite solar cells. EIMS changes the morphology of PbI₂ to improve the quality of perovskite film, as well as accelerate the extraction of electron, which leads to an efficiency of 22.1% with a negligible hysteresis behavior in the solar cells.

Imidazolium-based ionic liquids have been established as promising candidates for additives in perovskite solar cells. Herein, 1-(1-ethyl-3-imidazolium)propane-3-sulfonate (EIMS) zwitterionic ionic liquid is studied as additive to enhance the performance of the FAPbI₃ perovskite solar cells. The addition of EIMS leads to the generation of porous PbI₂ film, which promotes the reaction of PbI₂ with FAI solution and thus improves the quality of FAPbI₃ perovskite film during the two-step sequential spin coating. It is revealed that EIMS accelerates the extraction of electron, inhibits the formation of pinhole, and reduces the defect density, which leads to an increased efficiency of 22.1%. The hysteresis index is also reduced from 0.142 to 0.009, which indicates the addition of EIMS can realize a negligible hysteresis behavior in the solar cells. Moreover, devices prepared with EIMS retain above 96% of the original power conversion efficiency (PCE) value after being stored in dry air for 45 days. All these results demonstrate that the imidazolium-based zwitterionic ionic liquid additive strategy is a promising way for high-performance perovskite solar cells.

Three Se-containing nonfused electron acceptors are synthesized to systematically study the influences of the Se substitution on the intrinsic photoelectric properties and the photovoltaic performance of organic photovoltaic cells.

Selenium heterocycles are widely used in constructing organic semiconductors due to their advantages in narrowing the bandgap and enhancing the intermolecular packing. Herein, the application of Se substitution in designing nonfused electron acceptors (nfEAs) is studied. From a thiophene analog (A4T-16), three nfEAs with two (ASe-1 and ASe-2) or four (ASe-3) selenophene units are synthesized. The results suggest that the incorporation of Se atoms will downshift the lowest unoccupied molecular orbit level, upshift the highest occupied molecular orbit level, and exhibit redshifted absorption spectra due to the enhanced quinoidal character. The crystallographic data indicate that Se-containing molecules exhibit more planar conjugate skeleton and thus lead to the improvement of carrier mobility. When blended with a polymer donor PBDB-TF, ASe-1-, ASe-2-, and ASe-3-based organic photovoltaic (OPV) cells obtain power conversion efficiencies of 12.7%, 11.0%, and 10.4%, respectively. This work provides a comprehensive study of the application of Se substitution in designing low bandgap nfEAs for efficient OPV cells.

Organic solar cells (OSCs) have made dramatic improvements and interface engineering plays a crucial role. This review provides a comprehensive summary of the advancements in interface engineering, including the design of interfaces, the functionalities they offer, and their impact on device performance. Future challenges and potential research directions are outlined associated with interface engineering for large-area, high-performance, and cost-effective OSCs.

Abstract

Organic solar cells (OSCs) have made dramatic advancements during the past decades owing to the innovative material design and device structure optimization, with power conversion efficiencies surpassing 19% and 20% for single-junction and tandem devices, respectively. Interface engineering, by modifying interface properties between different layers for OSCs, has become a vital part to promote the device efficiency. It is essential to elucidate the intrinsic working mechanism of interface layers, as well as the related physical and chemical processes that manipulate device performance and long-term stability. In this article, the advances in interface engineering aimed to pursue high-performance OSCs are reviewed. The specific functions and corresponding design principles of interface layers are summarized first. Then, the anode interface layer, cathode interface layer in single-junction OSCs, and interconnecting layer of tandem devices are discussed in separate categories, and the interface engineering-related improvements on device efficiency and stability are analyzed. Finally, the challenges and prospects associated with application of interface engineering are discussed with the emphasis on large-area, high-performance, and low-cost device manufacturing.

Nature Communications, Published online: 04 March 2023; doi:10.1038/s41467-023-36917-y

Herein, as a bridge between tin oxide (SnO₂) and perovskite layer, P-biguanylbenzoic acid hydrochloride (PBGH) is adopted to enhance the conductivity of SnO₂ and the quality of the perovskite films by passivating defects at the interface. The FA_0.9Cs_0.1PbI₃-based solar cell exhibits a champion power conversion efficiency of 24.79%. This study provides a guidance for the design of buried interface passivators.

Abstract

The improvement of power conversion efficiency (PCE) and stability of the perovskite solar cell (PSC) is hindered by carrier recombination originating from the defects at the buried interface of the PSC. It is crucial to suppress the nonradiative recombination and facilitate carrier transfer in PSC via interface engineering. Herein, P-biguanylbenzoic acid hydrochloride (PBGH) is developed to modify the tin oxide (SnO₂)/perovskite interface. The effects of PBGH on carrier transportation, perovskite growth, defect passivation, and PSC performance are systematically investigated. On the one hand, the PBGH can effectively passivate the trap states of Sn dangling bonds and O vacancies on the SnO₂ surface via Lewis acid/base coordination, which is conducive to improving the conductivity of SnO₂ film and accelerating the electron extraction. On the other hand, PBGH modification assists the formation of high-quality perovskite film with low defect density due to its strong interaction with PbI₂. Consequently, the PBGH-modified PSC exhibits a champion power conversion efficiency (PCE) of 24.79%, which is one of the highest PCEs among all the FACsPbI₃-based PSCs reported to date. In addition, the stabilities of perovskite films and devices under high temperature/humidity and light illumination conditions are also systematically studied.

An effective additive molecule is designed with heterovalent substitution and antioxidant functions, whereby an organic metal coordination compound of tris(2,4-pentanedionato)gallium is employed to upgrade the quality of perovskite films and restrain the Sn²⁺ oxidation process. The perovskite solar cells exhibit a champion power conversion efficiency of 21.5% along with outstanding long-term stability.

Abstract

All-perovskite tandem solar cells are promising for breaking through the single-junction Shockley–Queisser limit, and that potentially raises interest in configuring efficient Sn-Pb alloyed narrow-bandgap perovskite solar cells (PSCs). However, the Sn-Pb alloyed perovskites are commonly plagued by uncontrollable crystallization dynamics and severe p-doping levels. Herein, an effective additive molecule is designed with heterovalent substitution and antioxidant functions, whereby an organic metal coordination compound of tris(2,4-pentanedionato)gallium (TPGa) is employed to upgrade the quality of perovskite films. Ga³⁺ substitution obviously boosts the formation energy of Sn vacancies and heals the trap states. Meanwhile, the crystal structure evolution process is improved by the anchoring effect of 2,4-pentanedionato. The PSCs incorporating these improvements deliver not only a power conversion efficiency of 21.5% but also outstanding stability, as demonstrated by retaining 80% of the initial efficiency for over 1500 h. In addition, 23.14%-efficient all-perovskite tandem solar cells are further obtained by pairing this PSC with a wide-bandgap (1.74 eV) top cell. This study supports the feasibility of doping trivalent ions into the Sn-Pb alloyed perovskites to compromise the self-p-doping effect and highlights the importance of acetylacetone for passivating defects and hindering oxidation.

To minimize energetic disorder in organic solar cells for higher efficiencies, accurate characterization is key. However, both the literature research and experimental results show that the two most common approaches to probing the energetic disorder, optical and electrical measurements, yield different results. With drift-diffusion simulations, the differences between the characterization techniques with their advantages but also limitations are explored.

Abstract

The energetic disorder has been known for decades to limit the performance of structurally disordered semiconductors such as amorphous silicon and organic semiconductors. However, in the past years, high-performance organic solar cells have emerged showing a continuously reduced amount of energetic disorder. While searching for future high-efficiency material systems, it is therefore important to correctly characterize this energetic disorder. While there are several techniques in the literature, the most common approaches to probe the density of defect states are using optical excitation as in external quantum efficiency measurements, or sequential filling of the tail states by applying an external voltage as in admittance spectroscopy. A metanalysis of available literature, as well as the experiments using four characterization techniques on two material systems, reveal that electrical, voltage-dependent measurements frequently yield higher values of energetic disorder than optical measurements. With drift-diffusion simulations, it is demonstrated that the approaches probe different energy ranges of the subband-gap density of states. The limitations of the techniques are further explored and it is found that extraction of information from a capacitance-voltage curve can be inhibited by internal series resistance. Thereby, the discrepancies between measurement techniques with sensitivity to different energy ranges and electronic parameters are explained.

A mixed diluent strategy is proposed to better compromise the charge generation and recombination for multicomponent organic photovoltaics (MC-OPVs), which involve a large bandgap and a low bandgap nonfullerene acceptors as diluent. This strategy improves balance between photocurrent and open-circuit voltage, and enables a power conversion efficiency of 19.76% (certified 19.41%), which represents a world record of single-junction OPV.

Abstract

The ternary blend is demonstrated as an effective strategy to promote the device performance of organic photovoltaics (OPVs) due to the dilution effect. While the compromise between the charge generation and recombination remains a challenge. Here, a mixed diluent strategy for further improving the device efficiency of OPV is proposed. Specifically, the high-performance OPV system with a polymer donor, i.e., PM6, and a nonfullerene acceptor (NFA), i.e., BTP-eC9, is diluted by the mixed diluents, which involve a high bandgap NFA of BTP-S17 and a low bandgap NFA of BTP-S16 (similar with that of the BTP-eC9). The BTP-S17 of better miscibility with BTP-eC9 can dramatically enhance the open-circuit voltage (V _OC), while the BTP-S16 maximizes the charge generation or the short-circuit current density (J _SC). The interplay of BTP-17 and BTP-S16 enables better compromise between charge generation and recombination, thus leading to a high device performance of 19.76% (certified 19.41%), which is the best among single-junction OPVs. Further analysis on carrier dynamics validates the efficacy of mixed diluents for balancing charge generation and recombination, which can be further attributed to the more diverse energetic landscapes and improved morphology. Therefore, this work provides an effective strategy for high-performance OPV for further commercialization.

A three-dimensional polymer passivation network was constructed by combining the bulk in situ polymerization and surface pre-polymerization/secondary polymerization strategies. The all-rounded passivation structure increased carrier diffusion length, promoted energy level alignment and carrier injection. Corresponding devices achieve a high open-circuit voltage of 1.194 V with an efficiency over 24 %, and module also achieves an efficiency of 21.55 %.

Abstract

The spontaneously formed uncoordinated Pb²⁺ defects usually make the perovskite films demonstrate strong n-type with relatively lower carrier diffusion length and serious non-radiative recombination energy loss. In this work, we adopt different polymerization strategies to construct three-dimensional passivation frameworks in the perovskite layer. Thanks to the strong C≡N⋅⋅⋅Pb coordination bonding and the penetrating passivation structure, the defect state density is obviously reduced, accompanied by a significant increase in the carrier diffusion length. Additionally, the reduction of iodine vacancies also changed the Fermi level of the perovskite layer from strong n-type to weak n-type, which substantially promotes the energy level alignment and carrier injection efficiency. As a result, the optimized device achieved an efficiency exceeded 24 % (the certified efficiency is 24.16 %) with a high open-circuit voltage of 1.194 V, and the corresponding module achieved an efficiency of 21.55 %.