Chen Weijie

Publication date: November 2021

Source: Nano Energy, Volume 89, Part B

Author(s): Francesco Bisconti, Antonella Giuri, Lorenzo Dominici, Sonia Carallo, Eleonora Quadrivi, Riccardo Po', Paolo Biagini, Andrea Listorti, Carola Esposito Corcione, Silvia Colella, Aurora Rizzo

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: 17 November 2021

Source: Joule, Volume 5, Issue 11

Author(s): Igal Levine, Amran Al-Ashouri, Artem Musiienko, Hannes Hempel, Artiom Magomedov, Aida Drevilkauskaite, Vytautas Getautis, Dorothee Menzel, Karsten Hinrichs, Thomas Unold, Steve Albrecht, Thomas Dittrich

An ultralow surface temperature on perovskite films is constructed, then surface perovskite lattice is etched by the condensed moisture. Therefore, PbI₂ is produced and type-I band alignment at the upper surface grain boundaries is formed, which significantly reduces the interface loss of carriers and improves the efficiency of perovskite solar cells to 23.2%.

Abstract

The open-circuit voltage (V _OC) of perovskite solar cells (PSCs) is reported to be significantly weakened by carrier loss at the film surface. Here, the moisture condensation at only the upper surface of perovskite films is controlled by constructing an ultralow surface temperature. Then, type-I band alignment can be formed at the surface grain boundaries due to the etching effect of trace amounts of condensed moisture. The beneficially constructed surface type-I band alignment can effectively repel carriers and return them to the inside of the grain, significantly avoiding the carrier loss at films surface. As a result, a superior carrier lifetime exceeding 2.5 µs is obtained and the V _OC of PSC is remarkably boosted from 1.07 to 1.17 V. The minimum V _OC deficit of only 0.39 V enables a substantial gain in power conversion efficiency (PCE) from 20.2% to 22.4% in one-step spin-coating methods. Moreover, this innovation is versatile and a champion PCE of 23.2% is also achieved in two-step spin-coating methods.

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.

In situ conversion of a 2D templating layer is used to fabricate lead-tin perovskite films highly ordered and with stoichiometric composition. The obtained highly crystalline lead-tin perovskites possess much enhanced environmental stability and promising photovoltaic performance, offering a considerable prospect to accelerate the commercialization of perovskite solar cells.

Abstract

Low bandgap lead-tin halide perovskites are predicted to be candidates to maximize the performance of single junction and tandem solar cells based on metal halide perovskites. In spite of the tremendous progress in lab-scale device efficiency, devices fabricated with scalable techniques fail to reach the same efficiencies, which hinder their potential industrialization. Herein, a method is proposed that involves a template of a 2D perovskite deposited with a scalable technique (blade coating), which is then converted in situ to form a highly crystalline 3D lead-tin perovskite. These templated grown films are alloyed with stoichiometric ratio and are highly oriented with the (l00) planes aligning parallel to the substrate. The low surface/volume ratio of the obtained single-crystal-like films contributes to their enhanced stability in different environments. Finally, the converted films are demonstrated as active layer for solar cells, opening up the opportunity to develop this scalable technique for the growth of highly crystalline hybrid halide perovskites for photovoltaic devices.

Realization of solution-processed halide perovskites transistors is challenging due to the presence of mobile ions. A generic strategy is demonstrated that can be applied for regulating ions in mixed ionic–electronic semiconductors and that enables the demonstration of perovskite transistors working at room-temperature by fixation of the mobile ions through ferroelectric polarization.

Abstract

Solution-processed halide perovskites have emerged as excellent optoelectronic materials for applications in photovoltaic solar cells and light-emitting diodes. However, the presence of mobile ions in the material hinders the development of perovskite field-effect transistors (FETs) due to screening of the gate potential in the nearby perovskite channel, and the resulting impediment to achieving gate modulation of an electronic current at room temperature. Here, room-temperature operation is demonstrated in cesium lead tribromide (CsPbBr₃) perovskite-based FETs using an auxiliary ferroelectric gate of poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)], to electrostatically fixate the mobile ions. The large interfacial polarization of the ferroelectric gate attracts the mobile ions away from the main nonferroelectric gate interface, thereby enabling modulation of the electronic current through the channel by the main gate. This strategy allows for realization of the p-type CsPbBr₃ channel and revealing the thermally activated nature of the hole charge transport. The proposed strategy is generic and can be applied for regulating ions in a variety of ionic–electronic mixed semiconductors.

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.

A rationally designed reductive molecule, 4-fluorophenylhydrazine hydrochloride (4F-PHCl), with multiple active sites for passivating defects, enhancing antioxidation, improving hydrophobicity, and minimizing nonradiative recombination in efficient and stable perovskite solar cells.

The defects (e.g., I₂, anion, and cation vacancies) in the perovskite films are detrimental to the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a multifunctional additive molecule 4-fluorophenylhydrazine hydrochloride (denoted as 4F-PHCl) is reported, which can improve perovskite crystallization, passivate film defects, and enhance film moisture stability, finally leading to the simultaneous increase in PCE and stability. It is revealed that the hydrazine functional group can effectively reduce the I₂ defects back to I^-. In addition, the hydrazinium contained cations and chloride anions can passivate the cationic defects (like anion vacancies) and anionic defects (like cation vacancies), respectively. The hydrophobic fluorinated benzene ring should be mainly responsible for the enhanced moisture stability of films and devices. As a result, the 4F-PHCl-modified device achieves a promising efficiency of 21.80% along with a high open-circuit voltage of 1172 mV and exhibits excellent long-term ambient stability. A guide for developing multifunctional additive molecules for the simultaneous enhancement of efficiency and stability is provided.

Perovskite solar cells are poised to take the next step into commercialization. Hole-transporting materials are central components of these devices, which determine the actual efficiency and durability by controlling interfacial charge extraction/transport processes and exchanges with the external environment. Herein, the evolution in the engineering of these layers is analyzed, revealing their “non-innocent role” in driving device performance.

The race to the future generation of low-cost photovoltaic devices continuously takes on added momentum with the appearance of novel practical solutions for the fabrication of perovskite solar cells (PSCs), a paradigm technology for ultracheap light-to-electricity conversion. Much has been done in the past few years toward defining standard protocols for the assessment of their efficiency and stability, aiming at achieving a worldwide consensus on the issue, that will allow reliable reporting of new data. While this is undoubtedly a step ahead toward commercialization of these devices, it also often triggers researchers to test record architectures using benchmark configurations, mainly for what regards the ancillary layers that extract electrical charges from the photoexcited perovskite. In particular, the mostly used hole-transporting material (HTM) is the small-molecule spiro-OMeTAD, which is also well known to be the origin of PSC degradation after prolonged operation. Herein, it is aimed to remark the huge impact of the HTM on PSC performance, recalling major issues associated with the conventional spiro-based one and providing an overview of state-of-the-art alternatives. Finally, possible scenarios for the future development of smart HTMs are also envisioned, as charge-extracting layers, with a real active role in ensuring PSC operational stability.

The mixed organic spacer cation n-butylammonium (BA) and 1-naphthalenemethylammonium (1-NMA) are introduced in 2D perovskites to manipulate the interlayer interactions between bulky spacer cations and inorganic slabs, leading to an efficient and air-stable 2D perovskite solar cell.

2D Ruddlesden–Popper (2DRP) perovskites with hydrophobic bulky cations are proven to improve the environmental stability in photovoltaic devices significantly. However, these spacer cations lead to a weak interplay in the 2DRP perovskites, severely impacting the charge carrier transport and require a systematic understanding of the interaction between spacer cations and inorganic slabs. Herein, a series of novel perovskites (BA_1−x NMA _x )₂MA₃Pb₄I₁₃ (NMA = 1-naphthalenemethylammonium, BA = n-butylammonium) are successfully fabricated to reveal the interaction of mixed spacers and inorganic slabs. Incorporating NMA cations enhances the NH⋯I⁻ hydrogen-bonding interaction between the spacer cations and [PbI₆]⁴⁻ slabs, resulting in a preferentially crystal vertical orientation of smoothed perovskite films with larger crystal grains. Thus, a significant reduction in the density of trap states of the resulting 2DRP perovskites is achieved which leads to highly efficient charge carrier transport. Consequently, the champion (BA_0.9NMA_0.1)₂MA₃Pb₄I₁₃ device yields a power conversion efficiency (PCE) of 14.21%, along with the unencapsulated devices that can retain 85% of their initial PCE for 1200 h under 35–65% relative humidity conditions. This work provides a simple and original method to modulate the interlayer interplay in 2DRP perovskites for highly efficient and air-stable perovskite solar cells.

Arising from the formation of strong PbCl bonding, chlorine terminated Ti₃C₂Cl _x MXenes are used as lattice “tape” to reduce the defects and release tensile strain located at interfaces and grain boundaries of CsPbBr₃ perovskite film, achieving a champion efficiency up to 11.08% with an ultrahigh voltage of 1.702 V for CsPbBr₃ perovskite solar cells.

Abstract

The crystal distortion such as lattice strain and defect located at the surfaces and grain boundaries induced by soft perovskite lattice highly determines the charge extraction-transfer dynamics and recombination to cause an inferior efficiency of perovskite solar cells (PSCs). Herein, the authors propose a strategy to significantly reduce the superficial lattice tensile strain by means of incorporating an inorganic 2D Cl-terminated Ti₃C₂ (Ti₃C₂Cl _x ) MXene into the bulk and surface of CsPbBr₃ film. Arising from the strong interaction between Cl atoms in Ti₃C₂Cl _x and the under-coordinated Pb²⁺ in CsPbBr₃ lattice, the expanded perovskite lattice is compressed and confined to act as a lattice “tape”, in which the PbCl bond plays a role of “glue” and the 2D Ti₃C₂ immobilizes the lattice. Finally, the defective surface is healed and a champion efficiency as high as 11.08% with an ultrahigh open-circuit voltage up to 1.702 V is achieved on the best all-inorganic CsPbBr₃ PSC, which is so far the highest efficiency record for this kind of PSCs. Furthermore, the unencapsulated device demonstrates nearly unchanged performance under 80% relative humidity over 100 days and 85 °C over 30 days.