Chen Weijie

Gas quenching is a promising technique for preparation of high-quality perovskite films in a large area, which are integrated in a production line by coupling with upscalable deposition methods.

Perovskite solar cells (PSCs) have made tremendous progress as a new-generation photovoltaic technology. The preparation of high-quality perovskite films plays a vital role in obtaining high performance of PSCs. Gas quenching is a facile, reproducible, and low-cost technique to realize the fabrication of high-quality perovskite films, thereby showing great potential in the application of highly efficient large-area PSCs. Herein, the development and application of gas-quenching technique for PSCs is reviewed and the recent progress on PSCs fabricated by gas quenching is summarized. Furthermore, the gas-quenching-related upscalable technique to fabricate large-area perovskite films and modules is presented. Finally, future research directions on high-efficiency perovskite solar cells based on the gas-quenching technique are discussed. Herein, a promising pathway for large-scale film deposition, which benefits the upscalable production of high-performance perovskite optoelectronic devices, is provided.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Po-Cheng Huang, Shao-Ku Huang, Ting-Chun Lai, Min-Chuan Shih, Hung-Chang Hsu, Chun-Hsiang Chen, Cheng-Chieh Lin, Chun-Hao Chiang, Chi-Ying Lin, Kazuhito Tsukagoshi, Chun-Wei Chen, Ya-Ping Chiu, Shiow-Fon Tsay, Ying-Chiao Wang

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Hongyu Jing, Wei Liu, Zhengyan Zhao, Jiangwei Zhang, Chao Zhu, Yantao Shi, Dingsheng Wang, Yadong Li

Herein, a fully low-temperature solution-processed colloidal SnO₂-assisted CdS electron transport layer for planar CH₃NH₃PbI₃ perovskite solar cells. The presence of SnO₂ underlayer allows the decrease in shunt current leakage and the formation of cascade band structure, which promote the electron extraction at the ETL/perovskite interface. The corresponding device delivers an appreciable efficiency of 16.26%, doubling that of conventional CdS-based device.

The cadmium sulfide (CdS) is a promising electron transport layer (ETL) material for perovskite solar cells (PSCs) due to its low photocatalytic activity toward perovskite materials under UV light. The critical problem responsible for the moderate performance of CdS-based PSCs is the parasitic light absorption of CdS, which drives researchers to deposit ultrathin ETLs. However, the ultrathin ETL often involves the undesirable shunt current leakage because of the direct contact between conducting substrate and perovskite layer. Herein, a fully low-temperature solution-processed colloidal SnO₂-assisted CdS (S-CdS) ETL for planar CH₃NH₃PbI₃ PSCs is constructed. The detailed characterizations of morphological, optical, and energy levels confirm that the assistance of colloidal SnO₂ provides the ameliorated continuity, reduces surface roughness and superior wettability of ETLs for high-quality perovskite formation as well as the favorable cascade band structure for efficient charge transfer. The study of charge transfer mechanisms reveals that the S-CdS ETL effectively inhibits the shunt leakage, promotes the electron extraction and suppresses the charge recombination at the ETL/perovskite interface. Consequently, the S-CdS ETL-based PSCs deliver an appreciable efficiency of 16.26%, doubling that of conventional CdS-based devices. To the best of our knowledge, this value is the champion efficiency reported for CdS-based CH₃NH₃PbI₃ PSCs.

The research progress on metal halide perovskite solar minimodules and their improvements in efficiency and stability is reviewed.

The rapid development of perovskite solar cells (PSCs) in view of efficiency during the past decade has made this emerging photovoltaic (PV) technology a promising competitor in the PV market. In the next step, PSCs need be manufactured into module scale to meet the commercialization requirements for further practical application. Demonstrations of perovskite solar modules (PSMs) and their improvements in efficiency and stability have recently become an intense area of research activities. Minimodules with the size suitable for laboratory investigation are naturally recognized as a desirable model for the study of PSMs. Herein, the recent progress and challenges in perovskite solar minimodules and the efforts to improve their scalable fabrication, efficiency, and stability are reviewed. Minimodule architectures, minimodule fabrication, and progress in the scalable deposition of perovskite and charge-transport layers as well as minimodule encapsulation are also discussed.

CsPbBr₃ perovskite quantum dots are synthesized and incorporated into PM6:Y6-BO organic solar cell (OSC) to enhance device efficiency from 16.4% to 17.1%, without scarifying the device stability due to the good structural stability of CsPbBr₃ perovskite quantum dots.

Among the emerging photovoltaic technologies, organic and perovskite quantum dots (PQDs) solar cells have thrived on low-cost processing and extraordinary optoelectronic properties. Herein, CsPbBr₃ PQDs are incorporated into PM6:Y6-BO organic solar cell (OSC) to enhance device efficiency without scarifying the device stability. While the incorporation of PQDs has no impact on the molecular packing and phase separation of organic semiconductors, their presence enhances light absorption due to the Rayleigh scattering effect, promotes exciton dissociation in the Y6-BO phase, and forms an efficient hole transfer pathway from Y6-BO to PQDs and then to PM6 to improve hole transport. These contribute to increased short-circuit current density (J _SC) and fill factor (FF) of OSCs with constant V _OC. With the presence of 1 wt% CsPbBr₃ PQDs doping, the highest power conversion efficiency (PCE) of the corresponding PM6:Y6-BO OSC is improved from 16.4% to 17.1%, where the device stability has not been affected due to the better phase stability of CsPbBr₃ PQDs than CsPbI₃ PQDs. This work unravels a new approach to enhance the efficiency of OSCs by applying PQDs doping to manipulate the photon-to-electricity conversion process.

A comparative study is conducted to investigate the role of solvent additive and thermal annealing (TA) treatments on the morphological and electrical properties of nonfullerene-based binary (PM6:Y7) and ternary (PM6:Y7:PC₇₀BM) photovoltaics. Inverse behavior is observed regarding mere TA treatment; however, superior efficiencies of both devices are exhibited due to the dual effect of 2% 1-chloronaphthalene additive along with TA.

Fine tuning of blend morphology is a key factor that limits the performance of the bulk-heterojunction organic photovoltaics (BHJ-OPVs). Herein, the morphological control of the binary (PM6:Y7) and ternary (PM6:Y7:PC₇₀BM) blends is conducted through 1-chloronaphthalene (CN) solvent additive and thermal annealing (TA) treatment with respect to their influence on the photovoltaic performance. Moreover, a distinct study is accomplished on the optical and electronic properties of the treated and nontreated binary and ternary devices by external quantum efficiency measurements and impedance spectroscopy. The results indicate that these treatments affect the performance of the binary and ternary OPVs differently. Regarding the 2% CN addition, the current density of the binary devices is improved by ≈27%, whereas the fill factor of the ternary devices shows a pronounced increment of ≈22%. A contradictory behavior is exhibited by TA for the binary and ternary OPVs. The PCEs for binary devices (with/without CN) and 2% CN-treated ternary ones are improved, while diminishing the PCEs of the ternary ones with 0% CN. Accordingly, the highest efficiencies of the binary and ternary OPVs are obtained due to the dual effect of 2% CN solvent additive along with the TA treatments.

In this research, polymer-based selenium-based solar cells (SSCs) have been presented and the efficiency of fabricated SSCs has been pushed to 4.3%. Through analyzing two equivalent circuit models, it could be found out that the suppressed recombination processes in the selenium layer could lead to higher performance of SSCs.

Abstract

Selenium(Se)-based solar cells (SSCs), known as one of the oldest solar cells, have regained intense attention due to the advantages of Se including direct bandgap, good stability, and single absorber. Among all kinds of device structures, conventional n-i-p SSCs with top organic hole transport layers (HTLs) show great potential since organic HTLs could be well-designed to smoothly extract holes from the Se single absorber and protect the Se surface. However, till now, the performance of Se solar cells with organic HTLs is not as good as expected. To address this issue, herein, the SSCs are first presented with organic polymers as the HTLs with the improved efficiency up to 4.3%, which is the highest one in organic HTLs-based SSCs. Additionally, comparing with perovskite solar cells, it is found that the recombination process is the key factor that influences the performance of SSCs. It is believed that the further optimization of the Se active layer and the design of new and suitable organic HTLs for SSCs should be the main focus to suppress the undesired recombination processes of Se films. Such realization would boost the efficiency of the as-fabricated SSCs.

Quasiplanar heterojunction (Q-PHJ) organic solar cells (OSCs) based on D18 and BTIC-BO-4Cl with a 3D network are reported, yielding a high power conversion efficiency (PCE) of 17.60%. The results show that the Q-PHJ architecture can replace the bulk heterojunction (BHJ) architecture to realize excellent OSCs for certain unique donors and acceptors, giving an alternative approach for photovoltaic material design and device fabrication.

Abstract

Bulk heterojunction (BHJ) organic solar cells (OSCs) have achieved great success because they overcome the shortcomings of short exciton diffusion distances. With the progress in material innovation and device technology, the efficiency of BHJ devices is continually being improved. For some special photovoltaic material systems, it is difficult to manipulate the miscibility and morphology of blend films, and this results in moderate, even poor device performance. Quasiplanar heterojunction (Q-PHJ) OSCs have been proposed to exploit the excellent photovoltaic properties of these materials. An OSC with BTIC-BO-4Cl has a 3D interpenetrating network structure with multiple channels that can facilitate the exciton diffusion and charge transport, and BTIC-BO-4Cl is therefore a good candidate for Q-PHJ OSCs. In this work, a D18:BTIC-BO-4Cl-based Q-PHJ device is fabricated. The exciton diffusion lengths of D18 and BTIC-BO-4Cl are in accord with the requirements of the Q-PHJ device and the efficiency of Q-PHJ device is as high as 17.60%. This study indicates that the Q-PHJ architecture can replace the BHJ architecture to produce excellent OSCs for certain unique donors and acceptors, providing an alternative approach to photovoltaic material design and device fabrication.

A “precursor to perovskite-like template to perovskite’ (PPP) strategy is proposed to control phase transition and to suppress deep-level defect formation during perovskite crystallization. The defect density is reduced by an order of magnitude and the carrier lifetime is doubled, yielding an impressive power conversion efficiency of 22.8%. Universality of this strategy is also demonstrated.

Tunable crystal growth offering highly aligned perovskite crystallites with suppressed deep-level defects is vital for efficient charge transport, which in turn significantly influences the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, a “precursor to perovskite-like template to perovskite” (PPP) growth strategy is developed, using either MAAc or GuaCl precursor to induce a sacrificial thermal–unstable perovskite-like template for (FAPbI₃) _x (MAPbI₃) _y perovskite growth. The self-sacrificed intermediate template induces the formation of highly aligned perovskite crystals with greatly enhanced film crystallinity and suppresses deep-level defect formation. Furthermore, it is proved that MAAc or GuaCl completely evaporates during the high-temperature annealing process. The reduction in defect densities and nonradiative recombination enhances both carrier lifetime and charge dynamics, yielding impressive PCEs of 22.3% and 22.8% with a high open-circuit voltage (V _OC) of 1.16 V and an incredible fill factor (FF) of 81.5% and 79.4% for MAAc- and GuaCl-based devices, respectively. These results suggest that the formation of the thermal–unstable perovskite-like sacrificial template is a promising strategy to restrain the deep-level defects in perovskite films toward the attainment of highly efficient and stable large-scale PSCs as well as other perovskite-based electronics.

The vacuum-deposited fluorinated analogue Spiro-OMeTAD is introduced as a hole transport layer in the inverted perovskite solar cells. Through the suitable energy level and improved crystallinity along the π–π stacking direction with the uniform surface morphology, the device performance and stability are notably improved. Furthermore, large-area and scalable device fabrication with good reliability is demonstrated using the all-vacuum deposition process.

Developing scalable technologies in perovskite solar cells (PSCs), including the deposition of uniform perovskite photoactive layers and charge transport layers, is critical for successfully migrating the recently developed advances in the PSC community toward industrialization. Herein, efficient and stable large-area PSCs using vacuum-deposited fluorinated analogue Spiro-OMeTAD (Spiro-mF) and methylammonium lead iodide (MAPbI₃) as hole transport and absorber layers, respectively, are demonstrated. The vacuum-deposited Spiro-mF exhibits improved crystallinity compared with the solution-processed counterpart through the enhanced molecular orientation along the π–π stacking direction, promoting the charge transport characteristics. Also, its uniform surface morphology contributes to the better quality crystallinity of the overlying perovskite film, which altogether leads to improved device performance and operational stability. Moreover, the all-vacuum deposition process allows the fabrication of large-area (250 mm²) and scalable (75 × 75 mm²) PSCs with excellent reliability in device performance.

A new polymer, PDTDT, is developed as hole-transporting material for CsPbI₂Br solar cells. Using PDTDT, an ultra-high efficiency of 17.36% with V _OC of 1.42 V under one sun and 34.20% with V _OC of 1.14 V under 200 lux indoor light are achieved. The PDTDT-based cells also show superior/comparable stability to dopant-free P3HT reference.

Abstract

To abate the issue of moisture-assisted phase transition of CsPbI₂Br, caused by hygroscopic dopants used in the hole-transporting material (HTM), developing dopant-free HTMs is necessary. In this work, a new polymer, PDTDT, is developed as a dopant-free HTM for CsPbI₂Br solar cells, and the device performance and stability are systematically compared with cells employing dopant-free P3HT. CsPbI₂Br solar cells using PDTDT show an efficiency of 17.36% with V _OC of 1.42 V and FF of 81.29%, which is one of the highest values for CsPbI₂Br cells. Moreover, a record-high efficiency of 34.20% with V _OC of 1.14 V under 200 lux indoor light illumination and efficiency of 14.54% (certified efficiency of 13.86%) for a 1 cm² device under one sun are accomplished. Importantly, PDTDT shows superior/comparable device stability to P3HT, promising its potential to be an alternative to popular doped Spiro-OMeTAD and P3HT HTM.

It is demonstrated that 1D perovskitoid based on 2-diethylaminoethylchloride cations can act as a template to induce 1D@3D perovskite structure, leading to smoother surface texture, longer charge-carrier lifetime, smaller residual tensile strain, and reduced surface-defect density in the perovskite film. With this strategy, highly efficient and stable 1D@3D PSCs with excellent reproducibility are realized.

Abstract

Longevity is a long-standing concern for organic–inorganic hybrid perovskite solar cells (PSCs). Recently, the use of low dimensional perovskite has been proven to be a promising strategy to improve the stability of PSCs. Herein, it is demonstrated that 1D perovskitoid based on 2-diethylaminoethylchloride cations can act as a template to induce 1D@3D perovskite structure, leading to smoother surface texture, longer charge-carrier lifetime, smaller residual tensile strain, and reduced surface-defect density in the perovskite film. With this strategy, highly efficient and stable 1D@3D PSC with excellent reproducibility, showing a champion power conversion efficiency (PCE) of 22.9% under standard AM 1.5 G one sun illumination is realized. The unencapsulated optimized devices can retain 94.7%, 92.4%, and 90.0% of their initial PCEs for 2100, 2200, and 2200 h under ambient air, 85 °C and illumination conditions, respectively.

Publication date: 15 September 2021

Source: Joule, Volume 5, Issue 9

Author(s): Pengqing Bi, Shaoqing Zhang, Zhihao Chen, Ye Xu, Yong Cui, Tao Zhang, Junzhen Ren, Jinzhao Qin, Ling Hong, Xiaotao Hao, Jianhui Hou

The suitability of substrate materials for co-evaporated perovskite solar cells is commonly assessed via heuristic approaches. Here, a universal guideline for the choice of substrate material is developed by investigating the thin-film formation of co-evaporated perovskite absorbers on various substrate materials. The guideline enables a targeted screening of substrate materials based on their surface characteristics enabling efficient all-evaporated perovskite solar cells.

Abstract

Vacuum-based deposition of optoelectronic thin films has a long-standing history. However, in the field of perovskite-based photovoltaics, these techniques are still not as advanced as their solution-based counterparts. Although high-efficiency vacuum-based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co-evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes—the substrate material—is studied. It is shown that not only the morphology of the co-evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co-evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum-processable hole transport material 2,2″,7,7″-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene is an ideal candidate for the fabrication of efficient all-evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co-evaporated perovskite thin films is suggested.

Direct solar hydrogen generation using a perovskite/Si tandem photovoltaic (PV) cell and Ni-based earth-abundant electrocatalysts achieves a record solar-to-hydrogen efficiency of 20%. The combination of the innovative “flower-stem” morphology of the NiMo catalyst, improves perovskite cell performance passivated by large organic cations and closed current matching with optimised tandem PV maximizes the overall hydrogen production efficiency.

Abstract

While direct solar-driven water splitting has been investigated as an important technology for low-cost hydrogen production, the systems demonstrated so far either required expensive materials or presented low solar-to-hydrogen (STH) conversion efficiencies, both of which increase the levelized cost of hydrogen (LCOH). Here, a low-cost material system is demonstrated, consisting of perovskite/Si tandem semiconductors and Ni-based earth-abundant catalysts for direct solar hydrogen generation. NiMo-based hydrogen evolution reaction catalyst is reported, which has innovative “flower-stem” morphology with enhanced reaction sites and presents very low reaction overpotential of 6 mV at 10 mA cm⁻². A perovskite solar cell with an unprecedented high open circuit voltage (V _oc) of 1.271 V is developed, which is enabled by an optimized perovskite composition and an improved surface passivation. When the NiMo hydrogen evolution catalyst is wire-connected with an optimally designed NiFe-based oxygen evolution catalyst and a high-performance perovskite-Si tandem cell, the resulting integrated water splitting cell achieves a record 20% STH efficiency. Detailed analysis of the integrated system reveals that STH efficiencies of 25% can be achieved with realistic improvements in the perovskite cell and an LCOH below ≈$3 kg⁻¹ is feasible.

A novel ferroelectric hardening method is proposed by precipitating a secondary phase inside of the ferroelectric grains. Akin to hindered dislocation motion in metals, domain wall motion in ferroelectrics is impeded and loss is reduced. The mechanical quality factor in the model system BaTiO₃–CaTiO₃ is enhanced by 1.5 times, while the piezoelectric coefficient and planar electromechanical coupling factor remain nearly unchanged.

Abstract

Domain wall motion in ferroics, similar to dislocation motion in metals, can be tuned by well-concepted microstructural elements. In demanding high-power applications of piezoelectric materials, the domain wall motion is considered as a lossy hysteretic mechanism that should be restricted. Current applications for so-called hard piezoelectrics are abundant and hinge on the use of an acceptor-doping scheme. However, this mechanism features severe limitations due to enhanced mobility of oxygen vacancies at moderate temperatures. By analogy with metal technology, the authors present here a new solution for electroceramics, where precipitates are utilized to pin domain walls and improve piezoelectric properties. Through a sequence of sintering, nucleation, and precipitate growth, intragranular precipitates leading to a fine domain structure are developed as shown by transmission electron microscopy, piezoresponse force microscopy, and phase-field simulation. This structure impedes the domain wall motion as elucidated by electromechanical characterization. As a result, the mechanical quality factor is increased by ≈50% and the hysteresis in electrostrain is suppressed considerably. This is even achieved with slightly increased piezoelectric coefficient and electromechanical coupling factor. This novel process can be smoothly implemented in industrial production processes and is accessible to simple laboratory experimentation for microstructure optimization and implementation in various ferroelectric systems.

A hydrophobic p-type semiconducting additive, fluorinated-gold-clusters, is used as a bifunctional interfacial mediator to efficiently modulate the carrier dynamics of perovskite and restrain the perovskite from degradation by external environmental stimuli, which results in an n–i–p perovskite solar cell with a champion efficiency up to 24.02% and moisture stability over 10 000 h in relative humidity of 75%.

Abstract

Tackling the interfacial loss in emerged perovskite-based solar cells (PSCs) to address synchronously the carrier dynamics and the environmental stability, has been of fundamental and viable importance, while technological hurdles remain in not only creating such interfacial mediator, but the subsequent interfacial embedding in the active layer. This article reports a strategy of interfacial embedding of hydrophobic fluorinated-gold-clusters (FGCs) for highly efficient and stable PSCs. The p-type semiconducting feature enables the FGC efficient interfacial mediator to improve the carrier dynamics by reducing the interfacial carrier transfer barrier and boosting the charge extraction at grain boundaries. The hydrophobic tails of the gold clusters and the hydrogen bonding between fluorine groups and perovskite favor the enhancement of environmental stability. Benefiting from these merits, highly efficient formamidinium lead iodide PSCs (champion efficiency up to 24.02%) with enhanced phase stability under varied relative humidity (RH) from 40% to 95%, as well as highly efficient mixed-cation PSCs with moisture stability (RH of 75%) over 10 000 h are achieved. It is thus inspiring to advance the development of highly efficient and stable PSCs via interfacial embedding laser-generated additives for improved charge transfer/extraction and environmental stability.