awn

Nickel oxide (NiO _x ) nanoparticles with high crystallinity and good dispersibility by the polymer network micro-precipitation method is synthesized, and the colloidal solution of ionic liquid-assisted NiO _x NPs dispersion is used to fabricate high-quality NiO _x films. Ultimately, the 1.01 cm² perovskite devices with the optimized NiO _x layers achieve the champion power conversion efficiency of 20.91% and 19.17% on rigid and flexible substrates, respectively.

Abstract

As one of the most promising hole transport layers (HTLs), nickel oxide (NiO _x ) has received extensive attention due to its application in flexible large-area perovskite solar cells (PSCs). However, the poor interface contact caused by inherent easy-agglomeration phenomenon of NiO _x nanoparticles (NPs) is still the bottleneck for achieving high-performance devices. Herein, a general strategy to synthesize NiO _x NPs with high crystallinity and good dispersibility via the polymer network micro-precipitation method is reported. Promisingly, this approach realizes the flow-division of precipitant and the restraint of the NPs motion, thereby effectively alleviating the coagulation phenomenon caused by excessive local concentration and secondary movement adsorption. Furthermore, the addition of ionic liquid not only inhibits the secondary aggregation of NiO _x NPs during the dispersion process, but also significantly enhances the properties of the colloidal solution. Ultimately, the 1.01 cm² PSCs based on the optimized NiO _x HTLs achieve the champion power conversion efficiency of 20.91% and 19.17% on rigid and flexible substrates, respectively. Moreover, the reproducibility and stability of PSCs are also significantly improved, especially for flexible devices. Overall, this strategy provides the possibility for flexible, large-area fabrication of high-quality NiO _x HTLs to promote the development of stable and efficient perovskite devices.

A novel approach for the fabrication of a monolithic photorechargeable supercapacitor with 11.5% efficiency is demonstrated. The three-electrode device comprises a p–i–n halide perovskite solar cell, smartly integrated with a mesoporous carbon-based double-layer capacitor. It attains simultaneous solar energy harvesting, conversion, storage, and on-demand release, showing the capability to mediate between intermittent supply and demand toward energy-autonomous devices.

The integration of solar cells with supercapacitors into hybrid monolithic power packs can provide energy autonomy to smart electronic devices of the Internet of Things (IoT) by mediating between intermittent load and supply. Herein, such a photorechargeable supercapacitor (also called a photosupercapacitor) is developed via a three-electrode integration of a p–i–n halide perovskite solar cell with a gel electrolyte-type supercapacitor that uses mesoporous N-doped carbon nanospheres (MPNC) as the active electrode material. Benefiting from the large surface area, well-defined mesoporous structure, and homogeneous particle size of the MPNC material, the supercapacitor demonstrates high capacitance, resulting in large energy and power densities with a high charge/discharge efficiency. Its integration with a large-area (1 cm²) FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ perovskite solar cell, with an optimized layer sequence to minimize degradation, results in a photosupercapacitor exhibiting fast (< 5 s) photocharging up to 1 V. The outstanding peak overall photoelectrochemical energy conversion efficiency of 11.5% is a result of a high solar cell power conversion efficiency of 12.5%, a high supercapacitor storage efficiency of 92%, and low internal energy losses due to monolithic integration. These results underline the high potential of this type of device toward application in the IoT.

The origin for the burn-in of non-fullerene-based organic solar cells is investigated. It is revealed that burn-in is mainly due to the rapid increase in the interfacial resistance (R _int). The R _int is greatly improved by constructing a ternary photoactive layer through the sequential deposition of a polymer solution and a binary acceptor solution.

Non-fullerene acceptor (NFA)-based organic solar cells often exhibit significant cell degradation in power conversion efficiency (PCE) in the early stages of operation, called “burn-in.” Generally, to fabricate NFA-based solar cells, binary blend solution deposition (binary BSD) of a conjugated polymer and an NFA is utilized. Herein, the reasons for burn-in are investigated by aging organic photovoltaic cells with independent control of temperature and light. The results reveal that burn-in is mainly due to a rapid increase in the interfacial resistance (R _int) rather than photo-oxidation of the components or oxidation of the electrode. This R _int is effectively suppressed by constructing a ternary photoactive layer through the sequential deposition of a polymer solution and a binary acceptor solution consisting of an NFA and a fullerene acceptor (ternary sequential deposition [ternary SqD]). Under the illumination of 1 sun and thermal annealing at 80 °C for 500 h, the binary BSD exhibits a reduction in efficiency of 63% and 59%, respectively, whereas the ternary SqD demonstrates a reduction of only 32% and 35%, respectively. In addition, the ternary SqD improves the PCE on using fullerene acceptors to enhance light harvesting at short wavelengths.

Two new acceptor–donor–acceptor (A–D–A)-type small molecule donors SM-DTBDT and SM-BDT with dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) and benzodithiophene (BDT) as the core D-units, respectively, are synthesized and their photovoltaic performance results indicate that tuning the center units of the donors can increase the efficiency and improve the stability of the all small-molecule organic solar cells.

Rational design and synthesis of new small-molecule donors are critically important to achieve highly efficient small-molecule organic solar cells (SM-OSCs) with desirable device stability. Herein, two new acceptor–donor–acceptor (A–D–A) structured small-molecule donor materials SM-DTBDT and SM-BDT with dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) and benzodithiophene (BDT) as the core D-units are designed and synthesized, respectively. After thermal annealing treatment, the power conversion efficiencies (PCEs) of the SM-DTBDT- and SM-BDT-based devices with Y8 as acceptor material reach 12.45% and 10.68%, respectively. The main reason for the different device performance can be ascribed to the different crystallinity and morphology features of the small-molecule donor:Y8 blend films. Compared with the SM-BDT:Y8 blend films, the SM-DTBDT:Y8 blend films show a smoother surface, more uniform phase separation, mixed edge-on and face-on orientations, and enhanced crystallinity, resulting in the more efficient exciton dissociation and charge transport. In addition, it is observed that the SM-DTBDT-based devices also exhibit better stability. This work shows that fine-tuning the center units of small-molecule donors can not only increase the photovoltaic performance but can also be an effective method to improve the device stability.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Xin Wang, Yuankun Qiu, Luyao Wang, Tiankai Zhang, Lei Zhu, Tong Shan, Yong Wang, Jinkun Jiang, Lingti Kong, Hongliang Zhong, Haomiao Yu, Feng Liu, Feng Gao, Feng Wang, Chun-Chao Chen

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Hailiang Wang, Huicong Liu, Zijing Dong, Tinglu Song, Weiping Li, Liqun Zhu, Yang Bai, Haining Chen

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Xiangkun Jia, Elizabeth Christine Baird, Jan Blochwitz-Nimoth, Sebastian Reineke, Koen Vandewal, Donato Spoltore

An environmentally benign material, histamine (HA), is used to intentionally passivate the V_I in the CsPbI_3−x Br _x perovskite thin films. The synergistic effect of Lewis base–acid interaction and H-bond strengthens the adsorption of HA molecules on the surface of perovskite. The fabricated PSCs with HA passivation significantly reduced the number of uncoordinated Pb²⁺ and achieved a record 20.8 % efficiency.

Abstract

Iodine vacancies (V_I) and undercoordinated Pb²⁺ on the surface of all-inorganic perovskite films are mainly responsible for nonradiative charge recombination. An environmentally benign material, histamine (HA), is used to passivate the V_I in perovskite films. A theoretical study shows that HA bonds to the V_I on the surface of the perovskite film via a Lewis base–acid interaction; an additional hydrogen bond (H-bond) strengthens such interaction owing to the favorable molecular configuration of HA. Undercoordinated Pb²⁺ and Pb clusters are passivated, leading to significantly reduced surface trap density and prolonged charge lifetime within the perovskite films. HA passivation also induces an upward shift of the energy band edge of the perovskite layer, facilitating interfacial hole transfer. The combination of the above raises the solar cell efficiency from 19.5 to 20.8 % under 100 mW cm⁻² illumination, the highest efficiency so far for inorganic metal halide perovskite solar cells (PSCs).

The 1-pyrenesulfonic acid sodium salt (PyNa⁺) is used to double-sided passivate the perovskite film to obtain a high device performance. By top-bottom management, the carrier lifetimes are prolonged and the defect density is effectively reduced. The device delivers a high efficiency of 21.22% and excellent stability holding 85% of its original efficiency after 1440 h in atmospheric environment.

In perovskite solar cells, not only defects on the top perovskite film surface seriously affect device performance, those buried in the bottom perovskite–electron-transfer layer (ETL) interface damage carrier extraction, transport, and device efficiency as well. Herein, a novel double-sided passivation strategy is designed using a single π-conjugation-induced 1-pyrenesulfonic acid sodium salt (PyNa⁺). It is found that it effectively passivates top and bottom interface defects to render high device performance. The π-conjugated pyrene-containing sodium salt electronically contributes to the surface band edges and influences the carrier dynamics by passivating defects at both top hole-transfer layer (HTL)–perovskite and bottom perovskite–ETL interfaces. The density functional theory (DFT) calculation confirms that the Pb cluster and I—Pb antisite defects can be effectively passivated by the O···Pb coordination and electrostatic interaction of PyNa⁺. The carrier lifetimes are prolonged, the interface defect density is effectively reduced as measured by space-charge-limited current (SCLC). Through the double layer passivation of PyNa⁺, the device delivers improved power conversion efficiencies of 21.22% relative to that of a reference perovskite, and enhanced stability with 85% of original efficiency after 1440 h in atmospheric environment. Double-sided passivation provides a comprehensive strategy for high-performance perovskite solar cells.

Amino trimethylene phosphonic acid and KOH are mixed (ATMP-K) to improve the performance of SnO₂ in perovskite solar cells (PSCs). ATMP-K boosts the power conversion efficiency of the PSCs from 20.99% to 23.52%. Furthermore, ATMP-K modified PSCs also show extraordinary ability to absorb Pb²⁺ ions after their degradation in water, offering a facile strategy for reducing Pb leakage.

Outstanding performance of perovskite solar cells (PSCs) is closely linked to the optoelectrical properties of charge transporting layers. Herein, amino trimethylene phosphonic acid (ATMP) and KOH are mixed (ATMP-K) and incorporated in a SnO₂ precursor solution to significantly improve the performance of the electron transport layer (ETL) SnO₂ in PSCs. Combining density functional theory (DFT) calculations and experiments, it is demonstrated that ATMP-K effectively passivates the oxygen vacancy and reduces the hydroxyl groups on the surface of SnO₂, resulting in a larger perovskite grain size and better energy-level alignment with perovskites. ATMP-K boosts the power conversion efficiency (PCE) of the PSCs from 20.99% to 23.52%. When applying in a perovskite/silicon heterojunction tandem solar cell, the device delivers an efficiency up to 24.75% with a high V _OC of 1.94 V, compared with 22.67% and 1.85 V of the reference cells. Furthermore, ATMP-K-modified PSCs also show extraordinary ability to absorb Pb²⁺ ions after their degradation in water, offering a facile strategy for reducing Pb leakage.

The Flory−Huggins parameters of two components, phase separation morphology and device performance of all-polymer solar cells (all-PSCs), are investigated for the first time. PC₇₁BM is used as a solid additive to boost the fill factor (FF) of all-PSCs based on PTzBI-oF:PFA1, as the strong interaction between PC₇₁BM and PTzBI-oF can decrease the phase separation of PTzBI-oF:PFA1 blend film.

Optimization of the photovoltaic performance of all-polymer solar cells (all-PSCs) includes delicate control of the film morphology of the light-harvesting layer. Although miscibility of polymer donors and polymer acceptors plays a critical role in the description of film morphology of all-PSCs, the mixing thermodynamics is unrevealed. Herein, we demonstrate that by incorporating 1% weight ratio of PC₇₁BM as the solid additive into the blends of electron-donating polymer PTzBI-oF and electron-accepting polymer PFA1, the miscibility of donor/acceptor can be improved by virtue of forming a favorable phase separation, which leads to an increased charge carrier transport and simultaneously enhanced fill factor. The maximum power conversion efficiency is thereby improved from 14.6% to 15.6%. The miscibility of two components in the photoactive layer can be quantitatively described using the Flory−Huggins interaction parameter (χ). In particular, a correlation between the Flory−Huggins parameters of the two components, in terms of phase separation morphology and device performance of all-PSCs, is established and the mechanism by which PC₇₁BM is added to this system is explored. This study establishes guidelines for the selection of solid additives when optimizing the efficiency of all-PSCs and promotes the integration and development of polymer physics and organic photovoltaics.

A percolative architecture of a Co₃O₄-SrCO₃ composite is applied as an efficient hole transport layer (HTL) for perovskite solar cells. The percolation of the dual phases offers nanosized hole transport pathways and optimized interfacial band alignments, enabling significantly improved charge collection compared with the single phase HTLs, leading to excellent photovoltaic performance.

Abstract

Perovskite solar cells (PSCs) are expected to profoundly impact the photovoltaic society on account of its high-efficiency and cost-saving manufacture. As a key component in efficient PSCs, the hole transport layer (HTL) can selectively collect photogenerated carriers from perovskite absorbers and prevent the charge recombination at interfaces. However, the mainstream organic HTLs generally require multi-step synthesis and hygroscopic dopants that significantly limit the practical application of PSCs. Here, a self-organized percolative architecture composed of narrow bandgap oxides (e.g., Co₃O₄, NiO, CuO, Fe₂O₃, and MnO₂) and wide bandgap SrCO₃ oxysalt as efficient HTLs for PSCs is presented. The percolation of dual phases offers nanosized hole transport pathways and optimized interfacial band alignments, enabling significantly improved charge collection compared with the single phase HTLs. As a consequence, the power conversion efficiency boosted from 8.08% of SrCO₃ based device and 15.47% of Co₃O₄ based device to 21.84% of Co₃O₄-SrCO₃ based one without notable hysteresis. The work offers a new direction by employing percolative materials for efficient charge transport and collection in PSCs, and would be applicable to a wide range of opto-electronic thin film devices.

Organic solar cells that employ donor:acceptor blends with near-zero driving force for charge transfer are becoming prevalent because of their superior performance. In this work, the factors affecting charge transfer and subsequent dissociation of the charge-transfer state are experimentally and theoretically analyzed. Short excited-state lifetime and hybridization open up new recombination channels with detrimental effects on free-charge generation.

Abstract

A blend of a low-optical-gap diketopyrrolopyrrole polymer and a fullerene derivative, with near-zero driving force for electron transfer, is investigated. Using femtosecond transient absorption and electroabsorption spectroscopy, the charge transfer (CT) and recombination dynamics as well as the early-time transport are quantified. Electron transfer is ultrafast, consistent with a Marcus–Levich–Jortner description. However, significant charge recombination and unusually short excited (S₁) and CT state lifetimes (≈14 ps) are observed. At low S₁–CT offset, a short S₁ lifetime mediates charge recombination because: i) back-transfer from the CT to the S₁ state followed by S₁ recombination occurs and ii) additional S₁–CT hybridization decreases the CT lifetime. Both effects are confirmed by density functional theory calculations. In addition, relatively slow (tens of picoseconds) dissociation of charges from the CT state is observed, due to low local charge mobility. Simulations using a four-state kinetic model entailing the effects of energetic disorder reveal that the free charge yield can be increased from the observed 12% to 60% by increasing the S₁ and CT lifetimes to 150 ps. Alternatively, decreasing the interfacial CT state disorder while increasing bulk disorder of free charges enhances the yield to 65% in spite of the short lifetimes.

Organic molecule dopants of fluorophenylboronic acids (F-PBAs) act as crystal cross-linkers between neighboring perovskite grains through hydrogen bonding and coordination bonding, yielding high-quality perovskite films with reduced grain boundary defects. Benefiting from the effective perovskite crystal cross-linking, a remarkable augmentation of the efficiency from 16.4% to nearly 20% has been achieved, while simultaneously enhancing moisture/thermal/light stability of MAPbI₃-based PSCs.

Abstract

Organic-inorganic metal halide perovskites are regarded as one of the most promising candidates in the photovoltaic field, but simultaneous realization of high efficiency and long-term stability is still challenging. Here, a one-step solution-processing strategy is demonstrated for preparing efficient and stable inverted methylammonium lead iodide (MAPbI₃) perovskite solar cells (PSCs) by incorporating a series of organic molecule dopants of fluorophenylboronic acids (F-PBAs) into perovskite films. Studies have shown that the F-PBA dopant acts as a cross-linker between neighboring perovskite grains through hydrogen bonds and coordination bonds between F-PBA and perovskite structures, yielding high-quality perovskite crystalline films with both improved crystallinity and reduced defect densities. Benefiting from the repaired grain boundaries of MAPbI₃ with the organic cross-linker, the inverted PSCs exhibit a remarkably enhanced performance from 16.4% to approximately 20%. Meanwhile, the F-PBA doped devices exhibit enhanced moisture/thermal/light stability, and specially retain 80% of their initial power conversion efficiencies after more than two weeks under AM 1.5G one-sun illumination. This work highlights the impressive advantages of the perovskite crystal cross-linking strategy using organic molecules with strong intermolecular interactions, providing an efficient route to prepare high-performance and stable planar PSCs.

Publication date: 15 September 2021

Source: Joule, Volume 5, Issue 9

Author(s): Ross A. Kerner, Zhaojian Xu, Bryon W. Larson, Barry P. Rand

The small bifunctional molecule 1,2-benzisothiazolin-3-one (BIT) is used as an additive and coverage layer, respectively, to enhance the performance and stability of the perovskite device. Both theoretical calculation and characterization of specimens indicate that the trap defect states are suppressed. The result of passivation strategy demonstrates a substantial enhancement in solar cell performance and stability.

Even though the perovskite material itself has a high defect tolerance compared with other semiconductors, the defects existing at grain boundaries (GBs) or the surface still cause high densities of the trap state which impair the efficiency and stability of perovskite solar cells (PSCs). Herein, the small molecule 1,2-benzisothiazolin-3-one (BIT) is investigated to passivate the defects at the GBs and surface of perovskite films. The results reveal that the BIT molecule belongs to a type of bifunctional species, which functions as cations and anions to passivate the perovskite surface. The BIT passivation generates lower formation energy and a more stable perovskite structure, resulting in improved performance and stability of the PSCs. The power conversion efficiency (PCE) of the optimized inverted photovoltaic device reaches 21.83%. Meanwhile, high photostability is achieved for PSCs with an efficiency drop of less than 10% under continuous light illumination over 500 h.