Chen Weijie

Introducing oxidized carbon soot (OCS)-based hole-transporting layer (HTL) to improve charge transport without charge recombination can improve the device performance in small- and large-sized organic photovoltaics (OPVs). Furthermore, large-sized and flexible OPVs with OCS-functionalized octadecylamine (OCS-ODA) HTL prepared by blade coating, show improved device performance and long-term stability (78% retention) under 1000 bending cycles.

Organic photovoltaics (OPVs) have recently advanced as promising solar cells owing to their many advantages, including the possibility of a low-temperature solution process, lightweight, and flexibility. In OPVs, the role of the interlayer is important for efficient charge transport from the photoactive layer to electrodes. However, as a hole-transporting layer (HTL), molybdenum oxide and poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) are still used for commercialization despite their drawbacks. The development of novel materials with suitable energy levels and solvent orthogonality is required to enhance hole extraction and optimize the film morphology. Herein, oxidized carbon soot (OCS) and OCS-functionalized octadecylamine (OCS-ODA) nanoparticles as HTL materials are synthesized. As a large number of oxygen functional groups are produced via Hummer's method, the devices with the OCS-ODA exhibit high hole extraction ability. The ODA long alkyl chains functionalized by facile process also improve film morphology to minimize contact resistance and charge recombination. The small-area (SA), large-area, and flexible (F) OPVs with OCS-ODA show power conversion efficiencies of 15.04%, 14.57%, and 12.73%, respectively. In particular, OPVs with OCS-ODA are further demonstrated to possess storage stability in SA-OPVs (71% retention after 450 h) and mechanical stability in F-OPVs (78% retention after 1000 bendings).

Using Cl additives is a beneficial strategy for the stabilization of the interfaces in planar perovskite solar cells. The encapsulated devices with Cl-doped perovskite absorber maintain 80% of the initial performance for >3470 h under continuous light soaking. Cl doping impairs the formation of PbI₂ and CsPbI₃ in CsFAPbI₃ after light soaking and suppresses the halogenation of the C₆₀ transport layer.

This article shows the new insights for stabilizing the p-i-n perovskite solar cells (PSCs) and modules based on double cation CsFAPbI₃ absorber using CsCl additives. The presence of chlorine in the perovskite crystal structure results in the decrease of the lattice parameters by 0.6 ± 0.06%, in the increase of the bandgap value (+0.018 eV), and charge carrier lifetimes with respect to the undoped one. The champion PSCs based on the CsFAPbI_3−x Cl _x absorber show an increase in power conversation efficiency from 18.06% up to 20.13% after Cl doping. The light-soaking stability of PSCs measured at maximum power point demonstrates impressive increase of the T80 from 1128 h for CsFAPbI₃-based devices to more than 3479 h for CsFAPbI_3−x Cl _x ones. It is found that the Cl doping suppresses the formation of lead iodide and pure CsPbI₃ induced by decomposition and phase segregation processes only when the perovskite is covered with the C ₆₀/BCP electron-transporting layer (ETL), while in the structure without ETL Cl additive is not effective. Finally, the high potential of Cl-anion engineering for the perovskite modules (5 × 5 cm²) is demonstrated, which shows promising 17.08% of power conversation efficiency and light-soaking stability for 1396 h.

Recent progress of interfacial solar evaporators applied in clean water production is summarized and reviewed based on solar–thermal materials with different conversion mechanisms. Critical factors in material and structural design of interfacial solar evaporators are discussed. At last, some perspectives related to further development of the field are provided.

Rational and sustainable utilization of resources is critical for the continuous development of this society. Solar energy, as one of the renewables, shows great potential in replacing part of the traditional energy supplies since it is clean, abundant, and easily convertible to thermal, electrical, and biological energies. Using solar energy as the green driving force, interfacial solar evaporation is a promising way for clean water production to alleviate global water shortage, taking advantage of its high evaporation efficiency (more than 80%) and strong adaptability toward various water sources and fields. In recent years, various kinds of materials with diverse designs have been synthesized and applied in interfacial solar evaporation for clean water production. Herein, recent progress in interfacial solar evaporators for clean water production is systematically reviewed, based on the photothermal conversion mechanisms of solar absorbers, including carbonous, semiconductor-based, and plasmatic ones. Furthermore, key design factors and strategies in interfacial solar evaporators are reviewed and discussed from material and structural design point of view, such as water transport, thermal management, latent heat for water vaporization, and salt accumulation. Finally, some perspectives related to resolving existing problems in the field are given.

Publication date: March 2023

Source: Nano Energy, Volume 107

Author(s): Lingbo Xiao, Xiaoli Xu, Zheng Lu, Jie Zhao, Ruiyuan Liu, Yaqi Ye, Rujun Tang, Wei-Qiang Liao, Ren-Gen Xiong, Guifu Zou

Publication date: March 2023

Source: Nano Energy, Volume 107

Author(s): Yunlong Ma, Rui Sun, Zhihao Chen, Sen Zhang, Dongdong Cai, Shuo Wan, Wenyuan Lin, Shu-Quan Zhang, Qisheng Tu, Wei Ma, Jie Min, Xiaotao Hao, Qingdong Zheng

Sodium selenosulfate is used as the selenium source to prepare antimony selenosulfide thin film. This facial method not only enables a remarkable efficiency of 10.05% with an ideal bandgap of 1.35 eV but also greatly reduces the production cost. The fabricated solar cells are with high stability.

Abstract

About 10% efficient antimony selenosulfide (Sb₂(S,Se)₃) solar cell is realized by using selenourea as a hydrothermal raw material to prepare absorber layers. However, tailoring the bandgap of hydrothermal-based Sb₂(S,Se)₃ film to the ideal bandgap (1.3–1.4 eV) using the selenourea for optimal efficiency is still a challenge. Moreover, the expensive selenourea dramatically increases the fabricating cost. Here, a straightforward one-step hydrothermal method is developed to prepare high-quality Sb₂(S,Se)₃ films using a novel precursor sodium selenosulfate as the selenium source. By tuning the Se/(Se+S) ratio in the hydrothermal precursor solution, a series of high-quality Sb₂(S,Se)₃ films with reduced density of deep defect states and tunable bandgap from 1.31 to 1.71 eV is successfully prepared. Consequently, the best efficiency of 10.05% with a high current density of 26.01 mA cm⁻² is achieved in 1.35 eV Sb₂(S,Se)₃ solar cells. Compared with the traditional method using selenourea, the production cost for the Sb₂(S,Se)₃ devices is reduced by over 80%. In addition, the device exhibits outstanding stability, maintaining more than 93% of the initial power conversion efficiency after 30 days of exposure in the atmosphere without encapsulation. The present work definitely paves a facile and effective way to develop low-cost and high-efficiency chalcogenide-based photovoltaic devices.

The popular donor used in organic solar cells PM6 is found an excellent dopant-free hole transport material in CsPbI₃ perovskite solar cells. As an alternative candidate for 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene, PM6's relative hydrophobic nature and interaction with perovskite through thiophene and fluorine functional groups can protect perovskite and improve the quality, thus leading to enhanced efficiency and stability of the corresponding devices.

Abstract

All-inorganic perovskite CsPbI₃ contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI₃ readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI₃ PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N₂ for 3000 h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.

Surface post-treatment via potassioum iodide manipulates the crystal growth process of Sb₂(S,Se)₃ light-absorbing layer to form compact films with larger grain size. It forms better band alignment and inhibits the formation of deep-level defects (Sb_Se), thereby improving the quality of heterojunction. The resultant solar cells deliver a remarkable champion power conversion efficiency of 9.22%.

Abstract

Antimony selenosulfide (Sb₂(S,Se)₃) has been emerging as a promising light absorber in the past few years owing to tunable bandgap (1.1–1.7 eV), high absorption coefficient (>10⁵ cm⁻¹) and excellent phase and environmental stability. However, the efficiency of Sb₂(S,Se)₃ solar cells lags far behind the Shockley–Queisser limit. One of the critical obstacles originates from various extrinsic and intrinsic defects. They mostly locate in the deep energy levels and are prone to form recombination centers, inhibiting the improvement of device performance. Herein, surface post-treatment via potassium iodide is introduced to fabricate high-quality Sb₂(S,Se)₃ films and solar cells. The surface post-treatment not only manipulates the crystal growth process to form compact films with larger grain size but also forms better band alignment and inhibits the formation of deep-level defects antimony antisite (Sb_Se), thus improving the quality of heterojunction. Consequently, the resultant Sb₂(S,Se)₃ solar cells achieve a champion power conversion efficiency of 9.22%. This study provides a new strategy of passivating deep-level intrinsic defects via surface post-treatment for high-efficiency Sb₂(S,Se)₃ solar cells.

Molten salt strategy enables the fabrication of perovskite solar cells by two-step sequential vacuum evaporation with exceptional reproducibility. The PSCs yield power conversion efficiencies of ≈24% and have good operational stability and shelf-life stability. The strategy has good expansibility in fabricating PSCs with tunable bandgaps.

Abstract

Vacuum evaporation is promising for the scalable fabrication of perovskite solar cells (PSCs). Nevertheless, the poor thermal conductivity of metal halide powder leads to unfavorable temperature inhomogeneity, which destabilizes the evaporation rate, posing a major challenge to the reproducible deposition of perovskite films, particularly by coevaporation. Herein, a molten salt strategy is reported for sequentially vacuum evaporation of PSCs. The molten salt increases the thermal conductivity of metal halides and greatly homogenizes the temperature, which stabilizes the evaporation rate and the composition of the resulting perovskite films. The PSCs yield power conversion efficiencies (PCEs) of ≈24% with exceptional reproducibility. The unencapsulated PSCs maintain 85% of the initial PCE after 3600 h of maximum power point tracking and maintain 85% of the initial PCE after being heated at 60 °C for 3000 h. The molten salt strategy opens a new avenue for the application of evaporation in perovskite optoelectronics.

Selective charge-carrier transport and extraction are essential in photovoltaic devices. Herein, a new electron transport layer configuration composed of two solution-processed n-type materials (PNDIT-F3N & Phen-NaDPO) is constructed for organic photovoltaic devices. This “n-n heterojunction” provides a built-in potential that enables cascade electron transport energy level alignment and enlarges the hole-blocking barrier, effectively boosting the power conversion efficiency.

Abstract

Selective electron transport and extraction are essential to the operation of photovoltaic devices. Electron transport layer (ETL) is therefore critical to organic photovoltaics (OPV). Herein, an ETL configuration is presented comprising a solution-processed n-n organic heterojunction to enhance electron transport and hole blocking, and boost power conversion efficiency (PCE) in OPV. Specifically, the n-n heterojunction is constructed by stacking a narrow-band n-type conjugated polymer layer (PNDIT-F3N) and a wide-band n-type conjugated molecule layer (Phen-NaDPO). Based on the ultraviolet photoelectron spectroscopy measurement and numerical simulation of current density-voltage characteristics, the formation of the built-in potential is investigated. In three OPVs with different active layers, substantial improvements are observed in performance following the introduction of this ETL configuration. The performance enhancement arises from the combination of selective carrier transport properties and reduced recombination. Another contributing factor is the good film-forming quality of the new ETL configuration, where the surface energies of the related materials are well-matched. The n-n organic heterojunction represents a viable and promising ETL construction strategy for efficient OPV devices.

Bottom Al₂O₃ and top poly (methyl methacrylate) (PMMA) passivations are adopted to improve the performance of the 2D perovskite-based photodiode. Much suppressed dark current and increased photocurrent are obtained by Al₂O₃ passivation. Device stability is improved by PMMA passivation. Responsivity and detectivity reach 0.36 A W⁻¹ and 5.4 × 10¹² Jones under 532 nm laser illumination at a power density of 1.5 nW cm⁻².

Abstract

2D perovskites have attracted intensive attention by virtue of their excellent optical and electrical properties along with good stabilities. Herein, a highly sensitive self-powered photodiode based on (PEA)₂(MA)₄Pb₅I₁₆ (PEA=C₆H₅(CH₂)NH₃, MA=CH₃NH₃) 2D perovskite is demonstrated by dual interface passivations. The Al₂O₃ bottom passivation can reduce the pinhole defects in the 2D perovskite film and suppress the trap-related recombination loss, bringing forward much reduced dark current and increased photocurrent. The poly (methyl methacrylate) (PMMA) top passivation can encapsulate the 2D perovskite film and thus improve the stability of the device. These results show that the 2D perovskite-based photodiode with dual interface passivations exhibits a large photo-to-dark current ratio of 10⁷, a fast response speed of 597 ns and a linear dynamic range of 160 dB without bias. Responsivity (R) and detectivity (D*) respectively reach 0.36 A W⁻¹ and 5.4 × 10¹² Jones under 532 nm laser illumination at a power density of 1.5 nW cm⁻². Moreover, the dual interface passivated device exhibits good stabilities. This study paves the road for developing low-cost, low-power, solution processed image sensors.

Highly efficient non-fused ring electron acceptor (NFREA)-based organic solar cells (OSCs) using a ternary approach by blending two in-house designed NFREAs with polymer donors are demonstrated. The two NFREAs tend to form an alloy-like phase that exhibits long exciton diffusion lengths and improved crystalline properties for efficient charge transfer while the 2PACz hole transport layer induces vertical phase separation.

Abstract

The construction of high-performance organic solar cells (OSCs) based on non-fused ring electron acceptors (NFREAs) is challenging despite their low synthesis complexity and low cost. Herein, highly efficient NFREA-based OSCs using a ternary approach by blending two in-house designed NFREAs called “C6C4-4Cl” and “BTIC-4F” with the donor PM6 are demonstrated. The two NFREAs with similar molecular skeletons tend to form an alloy-like phase that exhibits long exciton diffusion lengths and improved crystalline properties for efficient charge transfer. The complementary absorption spectra of the ternary system and energy transfer between the two NFREAs increases the current while the high lowest unoccupied molecular orbital (LUMO) energy level of BTIC-4F enhances the voltage of the OSCs. As a result, the ternary OSC with two NFREAs yields an impressive power conversion efficiency (PCE) of 15.62% using 2PACz as a hole transporting layer (HTL). Investigation of the buried interface reveals that 2PACz has a strong interaction with PM6 and induces vertical phase separation in the ternary blend. This work provides an effective strategy to improve the performance of NFREA-based OSCs by increasing the exciton diffusion length in an alloy-like acceptor phase and inducing vertical phase separation with the judicious selection of HTL.

Passivation and contact performance of double-textured tunnel oxide passivating contact (TOPCon) structures are promoted by rearranging the schedules of annealing processes and radio frequency powers of depositing SiO _x films, and the underlying mechanisms of charge-carrier transport on the textured structures are closely studied. The proof-of-concept perovskite/TOPCon tandem solar cells featuring double-textured structures are fabricated, yielding an outstanding efficiency of 28.49%.

Abstract

The ongoing success of tunnel oxide passivating contact (TOPCon) solar cells in the photovoltaic community in conjunction with the continuous advancements in the fabrication technologies of perovskite-based tandem devices make it possible to access highly-efficient perovskite/TOPCon tandem solar cells (TSCs). However, the development of such tandem solar cells is still in its infancy. One of the main challenges facing these devices is the balance of passivation and contact properties, especially on the textured crystalline silicon substrates. This article focuses on the double-textured TOPCon structures, and systematically investigates their passivation and contact properties with the purpose of balancing charge-carrier recombination and transport properties. The experiment results show that passivation and contact properties of the double-textured TOPCon structures can be well-regulated by means of rearranging the schedules of annealing processes and radio frequency powers of SiO _x deposition. The mechanisms of charge-carrier transport on the textured structures are closely studied, suggesting that charge carriers prefer to transport via the valleys of pyramids where the SiO _x layer is thin or missing. As a result, the proof-of-concept perovskite/TOPCon TSCs featuring the double-textured structures are successfully fabricated with a remarkable efficiency of 28.49%.

Structure-dependent effects of the four fullerene bisadduct regioisomers on the device performance of tin-based perovskite solar cells are systemically investigated. Benefiting from the favorable molecular packing, energy level alignment, and interfacial interaction, the trans-3-based devices yield a champion efficiency of 14.58% with a certified efficiency of 14.30%, representing one of the best-performing tin-based devices.

Abstract

Tin-based perovskite solar cells (TPSCs) are attracting intense research interest due to their excellent optoelectric properties and eco-friendly features. To further improve the device performance, developing new fullerene derivatives as electron transporter layers (ETLs) is highly demanded. Four well-defined regioisomers (trans-2, trans-3, trans-4, and e) of diethylmalonate-C₆₀ bisadduct (DCBA) are isolated and well characterized. The well-defined molecular structure enables us to investigate the real structure-dependent effects on photovoltaic performance. It is found that the chemical structures of the regioisomers not only affect their energy levels, but also lead to significant differences in their molecular packings and interfacial contacts. As a result, the devices with trans-2, trans-3, trans-4, and e as ETLs yield efficiencies of 11.69%, 14.58%, 12.59%, and 10.55%, respectively, which are higher than that of the as-prepared DCBA-based (10.28%) device. Notably, the trans-3-based device also demonstrates a certified efficiency of 14.30%, representing one of the best-performing TPSCs.