Chen Weijie

A low-cost electron acceptor of TBT-2 is designed and synthesized, which has deep highest occupied molecular orbital level, low optical gap, and strong π–π stacking between terminal groups. The TBT-2-based device exhibits a power conversion efficiency of 13.25%, which is as high as those of the state-of-art electron acceptors on the premise of their similar optical gaps.

Abstract

To develop the low-cost nonfullerene acceptors (NFAs), two fully non-fused NFAs (TBT-2 and TBT-6) with ortho-bis((2-ethylhexyl)oxy)benzene unit and different side chains onto thiophene-bridges are synthesized through highly efficient synthetic procedures. Both acceptors show good planarity, low optical gaps (≈1.51 eV), and deep highest occupied molecular orbital levels (≤-5.77 eV). More importantly, the single-crystal structure of TBT-2 shows compact molecular arrangement due to the existence of intramolecular interactions between adjacent aromatic units and strong π–π stacking between intermolecular terminal groups. When the two acceptors are fabricated organic photovoltaic (OPV) cells by combining with a wide optical gap polymer donor, the TBT-6 with strong crystallization forms large domain sizes in bulk heterojunction (BHJ) blend. As a result, the TBT-6-based OPV cell shows a low power conversion efficiency (PCE) of 9.53%. In contrast, the TBT-2 with proper crystallization facilitates morphological optimization in the BHJ blend. Consequently, the TBT-2-based OPV cell gives an outstanding PCE of 13.25%, which is one of the best values among OPV cells with similar optical gaps. Overall, this work provides a practical molecular design strategy for developing high-performance and low-cost electron acceptors.

Publication date: July 2023

Source: Nano Energy, Volume 112

Author(s): Minje Kim, Sol Lee, Viet Anh Cao, Min Cheol Kim, Junghyo Nah

Pseudohalide ions can modulate the facets during crystallization, forming a (001) dominated surface. The regulation is due to larger binding energy at the high index facets, inducing preferential growth along (001) direction. Less intrinsic defects are found resulting in PCE of 24.11% and V _oc of 1.181 V with slightly enhanced stability.

Abstract

Formamidinium lead triiodide (α-FAPbI₃) has been widely used in high-efficiency perovskite solar cells due to its small band gap and excellent charge-transport properties. Recently, some additives show facet selectivity to generate a (001) facet-dominant film during crystallization. However, the mechanism to realize such (001) facet selectivity is not fully understood. Here, the authors attempted to use three ammonia salts NH₄X (X are pseudohalide anions) to achieve better (001) facet selectivity in perovskite crystallization and improved crystallinity. After addition, the (001) facet dominance is generally increased with the best effect from SCN⁻ anions. The theoretical calculation revealed three mechanisms of such improvements. First, pseudohalide anions have larger binding energy than the iodine ion to bind the facets including (110), (210), and (111), slowing down the growth of these facets. The large binding energy also reduces nucleation density and improves crystallinity. Second, pseudohalide ions improve phase purity by increasing the formation energies of the δ-phase and other hexagonal polytypes, retarding the α- to δ-phase transition. Third, the strong binding of these anions can also effectively passivate the iodine vacancies and suppress nonradiative recombination. As a result, the devices show a power conversion efficiency of 24.11% with a V _oc of 1.181 V.

The strategies for stretchable “crack-free” intrinsically stretchable organic solar cells (IS-OSCs) are proposed. By improving the physical and chemical adhesion between thermoplastic polyurethane substrate and poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate), crack-free IS-OSCs under 40% strain are successfully fabricated and a high power conversion efficiency (PCE) of 10.2% and high stretchability that retain 70% of an initial PCE under 44% strain are demonstrated.

Abstract

Intrinsically stretchable organic solar cells (IS-OSCs) have been recently spotlighted for their omnidirectional stretchability, seamless integrability to any surface, and facile fabrication. Due to these attributes, IS-OSCs are ideal off-grid power sources, especially for wearable electronics in real-life. However, under human body elongation as high as ≈40%, cracks in IS-OSCs are considered inevitable, and the origin of the mechanical failure is rarely identified. Herein, the crack-initiation and the propagation mechanism are first clarified. Based on this, a crack-free substrate/transparent electrode platform for stretchable electronics is also suggested. A double-locking scheme, which reinforces the physical/chemical adsorption within the most mechanically fragile layer, a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and also with thermoplastic polyurethane substrate, is introduced. As a result, the crack-onset strain of double-locked IS-OSCs surpasses 40%, while that of pristine ones is less than 20%. The IS-OSCs with the double-locked system exhibits an efficient power conversion efficiency of 10.2%, and the absence of cracks allows the IS-OSCs to maintain 79.7% of the initial PCE at 40% strain.

Publication date: 17 May 2023

Source: Joule, Volume 7, Issue 5

Author(s): Kai Liu, Saqib Rafique, Stefania F. Musolino, Zenghua Cai, Fengcai Liu, Xiaoguo Li, Yongbo Yuan, Qinye Bao, Yingguo Yang, Jiao Chu, Xinxin Peng, Cengao Nie, Wei Yuan, Sidi Zhang, Jiao Wang, Yiyi Pan, Haijuan Zhang, Xia Cai, Zejiao Shi, Chongyuan Li

A nonfullerene molecule IO-4Cl with the n-type semiconductor property and hydrophobic characteristics is first introduced to reduce defects, improve electron transport, and prevent the decomposition of perovskite films under moisture conditions. The tin perovskite solar cells with IO-4Cl achieve an increased power conversion efficiency from 8.14% to 11.49%, maintaining 70% of its initial value for 350 h under 30% relative humidity.

Tin-based perovskites have emerged as the most promising lead-free perovskite materials due to the characteristics of the environmentally friendly and more suitable bandgap. However, the power conversion efficiency still lags behind the lead perovskite owing to unfavorable defects of the perovskite film and poor interface contact between tin perovskite and electron transporting layers. Herein, an n-type conjugated nonfullerene molecule, termed IO-4Cl, is developed for efficient and stable tin perovskite solar cells (TPSCs). The IO-4Cl possesses electron-donating functional groups that can enlarge grain size and passivate defect states of perovskite films through Lewis acid–base interactions. Besides, the IO-4Cl exhibits an appropriate lowest unoccupied molecular orbital level and interface-modification ability, enabling superior electron extraction and transport ability of TPSCs. More importantly, the hydrophobic characteristic of IO-4Cl prevents the decomposition of perovskite films under moisture conditions, improving the moisture stability of TPSCs. Consequently, the TPSCs with IO-4Cl achieve a champion efficiency of 11.49% with an open-circuit voltage increase of 100 mV, and excellent moisture stability under ambient air condition with 30% relative humidity, without encapsulation. The work provides a new inspiration for the introduction of functional nonfullerene materials to obtain highly efficient and stable TPSCs.

NIR-transparent perovskite solar cells with power conversion efficiency (PCE) > 17% and excellent stability are demonstrated. 4T silicon/perovskite tandem solar cell with PCE > 26% is fabricated over an area of ≈80 mm². Top transparent-contact is deposited via industry-compatible process at room temperature. Also, silver electrode is replaced with copper to reduce the production cost.

Si-perovskite tandem photovoltaic devices in the four-terminal (4T) configuration could proffer a solution to the problems associated with the stability gap between the component perovskite and Si devices. The fabrication of NIR-transparent perovskite solar cells (PSCs) with the stable triple cation perovskite as the photo-absorber and subsequent integration with a Si solar cell in a 4T tandem device is reported. The critical development of the sputtered top transparent conducting electrode (TCE) layer and oxide buffer layer at room temperature (25 °C) leads to reproducible, highly efficient NIR-transparent PSCs of both small area (0.175 cm²) with power conversion efficiency (PCE) of 17.1% and large area (0.805 cm²) with PCE of 16.0%. Electrically disparate, optically coupled 4T tandem devices of the optimized PSCs with commercial monocrystalline PERC Si solar cells exhibit greater than 26% PCE. In addition to enabling industry-compatible TCE-based low-cost Si/perovskite tandem photovoltaics, this study could also be the gateway for the potential use in niche applications like building integrated photovoltaics.

Nonhalide lead source of lead acetate is developed for fabricating high-quality Ruddlesden–Popper perovskite films for efficient solar cells. By introducing dimethyl sulfoxide in the lead acetate–based precursor solution to regulate the crystallization process, the film exhibits significantly improved quality with enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution.

The 2D Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, are emerging photovoltaic materials because of their highly tunable optoelectronic properties and improved stability compared to their 3D counterparts. Nonhalide lead sources attract increasing attention in 3D perovskites, whereas the lead sources for RPPs are limited to lead halides. Herein, nonhalide lead source of lead acetate is investigated for high-quality RPP films by a dimethyl sulfoxide (DMSO)-assisted delayed annealing process. The incorporation of DMSO in the lead acetate–based precursor solution regulates the crystallization process, resulting in RPP films with distinctly enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution. Consequently, the optimized RPP solar cell with an inverted planar structure delivers a champion power conversion efficiency of 17.3%. Herein, future developments of nonhalide lead sources are spurred to fabricate RPP films with high device performance.

The combined-accelerated stress testing (C-AST) chamber shown is used to evaluate the durability of photovoltaic (PV) modules including degradation modes that are not found in standardized tests. The acceleration factors for C-AST of PV modules in the Florida, USA environment for the mechanisms of ultraviolet photodegradation and hydrolysis of backsheet layers, electrochemical corrosion, and PbSn solder interconnect fatigue are established.

Combined-accelerated stress testing (C-AST) is developed to establish the durability of photovoltaic (PV) products, including for degradation modes that are not a priori known or examined in standardized tests. C-AST aims to comprehensively represent the sample, stress factors, and their combinations using levels at the statistical tails of the natural environment. Acceleration factors for relevant climate sequences within the C-AST cycle with respect to the Florida USA climate are estimated for selected degradation mechanisms. It is found that for degradation of the outer backsheet polymer layer, the acceleration factor of the tropical climate sequence (the longest of the climate sequences) is f (T, G) = 17.3 with ultraviolet photodegradation; for polyethylene terephthalate hydrolysis (backsheets), f (T, RH) = 426; for electrochemical corrosion (PV cell), f (I) = 14.1; and for PbSn solder fatigue f (ΔT, r (T)) = 17.3. Here, T is the module temperature, G is the broadband spectrum irradiance on the plane of array of the module, RH is the relative humidity on the module surface, I is the leakage current through the module packaging, and r(T), the number of temperature reversals. The methods discussed herein are generally applicable for evaluating acceleration factors in other accelerated test methods.

Two salts, namely, sodium methanesulfonate (SMSO) and sodium methanesulfinate (SMSI), are adopted as modifiers for the printable mesoscopic perovskite solar cells. The differences in their anion structures and the valence states of the central S atoms result in different coordination abilities and passivation effects with perovskite. Ultimately, the sulfite outperforms the sulfonate on the device performance enhancement.

High-performance perovskite solar cells require the modification of grain boundaries in the polycrystalline light absorbing layer and salt modifiers have contributed a lot toward this requirement. Herein, the application of the sodium methanesulfinate (SMSI) as the modifier for the hole-conductor-free printable mesoscopic perovskite solar cell (p-MPSC) with a carbon electrode is reported. It is found that SMSI prevents the oxidization of iodine ions in the precursor and methanesulfinate coordinates more strongly than methanesulfonate with perovskite. The interaction between SMSI and perovskite brings improved crystallinity and reduced defects, and thereby suppresses nonradiative recombination in p-MPSCs. At the same time, SMSI also shifts the Fermi level of perovskite downward and contributes to an optimized energy-level alignment for promoted charge injection. By introducing the SMSI modifier, the power conversion efficiency of p-MPSCs from 16.6% to 18.1% is successfully improved. The research indicates that the methanesulfinate anion is a promising candidate for salt modifier design serving high-performance PSCs.

Highly efficient inverted perovskite solar cells and large area modules are developed by designing low-temperature, scalable, and uniform chemical bath deposition NiO _X thin films, which are obtained by amino-alcohol ligands based controllable Ni²⁺ release and deposition. A further surface modification for better energy level alignment enhances the module efficiency up to 19% with an area of 18.1 cm².

Abstract

A scalable and low-cost deposition of high-quality charge transport layers and photoactive perovskite layers are the grand challenges for large-area and efficient perovskite solar modules and tandem cells. An inverted structure with an inorganic hole transport layer is expected for long-term stability. Among various hole transport materials, nickel oxide has been investigated for highly efficient and stable perovskite solar cells. However, the reported deposition methods are either difficult for large-scale conformal deposition or require a high vacuum process. Chemical bath deposition is supposed to realize a uniform, conformal, and scalable coating by a solution process. However, the conventional chemical bath deposition requires a high annealing temperature of over 400 °C. In this work, an amino-alcohol ligand-based controllable release and deposition of NiO _X using chemical bath deposition with a low calcining temperature of 270 °C is developed. The uniform and conformal in-situ growth precursive films can be adjusted by tuning the ligand structure. The inverted structured perovskite solar cells and large-area solar modules reached a champion PCE of 22.03% and 19.03%, respectively. This study paves an efficient, low-temperature, and scalable chemical bath deposition route for large-area NiO _X thin films for the scalable fabrication of highly efficient perovskite solar modules.

A passivation strategy using polar molecular phenmethylammonium iodide (PMAI) is introduced to enhance performance of FA-MA hybrid (FA: HC(NH₂)₂; MA: CH₃NH₃) perovskite solar cells. The dipole-induced equivalent passivation effect is revealed successfully by PMAI and an applicable role of polar molecular passivators is declared. Overall, combining the molecular-bonding defect passivation effect, the PMAI leads to a tremendous increase over 100 mV in V _OC.

Abstract

To date, the improvement of open-circuit voltage (V _OC) offers a breakthrough for the performance of perovskite solar cells (PSCs) toward their theoretical limit. Surface modification through organic ammonium halide salts (e.g., phenethylammonium ions PEA⁺ and phenmethylammonium ions PMA⁺) is one of the most straightforward strategies to suppress defect density, thereby leading to improved V _OC. However, the mechanism underlying the high voltage remains unclear. Here, polar molecular PMA⁺ is applied at the interface between perovskite and hole transporting layer and a remarkably high V _OC of 1.175 V is obtained which corresponds to an increase of over 100 mV in comparison to the control device. It is revealed that the equivalent passivation effect of surface dipole effectively improves the splitting of the hole quasi-Fermi level. Ultimately the combined effect of defect suppression and surface dipole equivalent passivation effect leads to an overall increase in significantly enhanced V _OC. The resulted PSCs device reaches an efficiency of up to 24.10%. Contributions are identified here by the surface polar molecules to the high V _OC in PSCs. A fundamental mechanism is suggested by use of polar molecules which enables further high voltage, leading ways to highly efficient perovskite-based solar cells.

1,3-dimethyl-imidazolidinone (DMI) is employed as an additive in the perovskite precursor ink to stabilize the intermediate phase for scalable production of high-efficiency perovskite solar mini-modules. This approach allows blade coating of large-area, uniform, and pinhole-less perovskite films, enabling 23.4% and 20.1% power conversion efficiencies for the best-performing unit cell and module with n-i-p configuration, respectively.

Abstract

Blade coating of perovskite solar cells (PSCs) and modules has progressed considerably toward the industrial production of perovskite photovoltaics. Developing stable perovskite precursors is critical for achieving uniform coating over large areas. Here, the engineering of a perovskite precursor solution consisting of 2-methoxyethanol (2-Me) and 1,3-dimethyl-imidazolidinone (DMI) with superior intermediate phase stability that enables scalable production of efficient perovskite solar modules is reported. With this perovskite precursor solution, uniform and pinhole-less perovskite film is deposited over a large area of > 100 cm² and higher-efficiency PSCs and modules are obtained. The best-performing unit cell and module with n-i-p configuration reach power conversion efficiencies of 23.4% and 20.1%, respectively. Additionally, a series of non-destructive metrology methods, such as spectroscopic ellipsometry, hyperspectral photoluminescence, electroluminescence, and laser beam-induced current mapping, are employed to assess and guide the development the blade-coated perovskite modules. This results show that rational engineering of precursor inks for blade coating is promising for the scalable production of efficient perovskite solar modules.

A surface reconstruction strategy is employed to achieve a strain-free perovskite film with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. The resultant monolithic perovskite/black-silicon tandem realizes a certified stabilized efficiency ≈29.0%, which is among the best performances for perovskite/silicon tandems based on tunnel oxide passivated contacts.

Abstract

Despite the swift rise in power conversion efficiency (PCE) to more than 32%, the instability of perovskite/silicon tandem solar cells is still one of the key obstacles to practical application and is closely related to the residual strain of perovskite films. Herein, a simple surface reconstruction strategy is developed to achieve a global incorporation of butylammonium cations at both surface and bulk grain boundaries by post-treating perovskite films with a mixture of N,N-dimethylformamide and n-butylammonium iodide in isopropanol solvent, enabling strain-free perovskite films with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. As a result, the corresponding single-junction perovskite solar cells yield a champion PCE of 21.8%, while maintaining 100% and 81% of their initial PCEs without encapsulation after storage for over 2500 h in N₂ and 1800 h in air, respectively. Remarkably, a certified stabilized PCE of 29.0% for the monolithic perovskite/silicon tandems based on tunnel oxide passivated contacts is further demonstrated. The unencapsulated tandem device retains 86.6% of its initial performance after 306 h at maximum power point (MPP) tracking under continuous xenon-lamp illumination without filtering ultraviolet light (in air, 20–35 °C, 25–75%RH, most often ≈60%RH).

Nature Communications, Published online: 22 April 2023; doi:10.1038/s41467-023-37738-9

Publication date: 19 April 2023

Source: Joule, Volume 7, Issue 4

Author(s): Yiwen Wang, Joel Luke, Alberto Privitera, Nicolas Rolland, Chiara Labanti, Giacomo Londi, Vincent Lemaur, Daniel T.W. Toolan, Alexander J. Sneyd, Soyeong Jeong, Deping Qian, Yoann Olivier, Lorenzo Sorace, Ji-Seon Kim, David Beljonne, Zhe Li, Alexander J. Gillett

Nature Materials, Published online: 20 April 2023; doi:10.1038/s41563-023-01524-1

Nature Materials, Published online: 20 April 2023; doi:10.1038/s41563-023-01531-2

Nature Energy, Published online: 20 April 2023; doi:10.1038/s41560-023-01254-3

Carbonyl passivation of uncoordinated lead and inhibition of ion migration by amino groups achieve better effects. The champion performance of device based on 5-ADI additive achieved 22.42%

Perovskite solar cells (PSCs) have been developing rapidly in recent years, in which the choice of additives plays a crucial role. Herein, a new small molecule is introduced named 5-ADI with amino and carbonyl groups as an additive for perovskite. Specifically, the carbonyl group in 5-ADI can interact with undercoordinated Pb²⁺ to passivate the perovskite defects. Moreover, the amino group can effectively immobilize I⁻ atoms and inhibit ion migration, and it can synergistically passivate defects and improve photovoltaic performance. Meanwhile, the 5-ADI treatment makes energy levels match well. Consequently, high-quality perovskite film with fewer defects is produced due to 5-ADI treatment improves the crystallinity of perovskite. The device fabricated with 5-ADI additive achieves a power conversion efficiency of 22.42%. Besides, 5-ADI can act as a barrier against water to promote perovskite moisture stability. In general, a superior strategy for defect passivation in PSCs is provided.