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2D perovskite/organic heterojunction (PEA₂SnI₄/Y6) ambipolar synapse phototransistors are fabricated via a fully solution process and have outstanding application in the visible-NIR color recognition systems. It is the first time to realize “G,” “o,” “o,” and “d” which are encoded by red/green/blue/NIR light via dual-mode simulation of learning process, proving great potential to simulate the artificial intelligence vision systems of the robot.

Abstract

Artificial intelligence vision systems (AIVSs) with information sensing, processing, and storage functions are increasingly gaining attention in the science and technology community. Although synapse phototransistor (SPT) is one of the essential components in AIVSs, solution-processed large-area photonic synapses that can detect and recognize multi-wavelength light are highly desirable. One of the major challenges in this area is the inability of the available materials to distinguish colors from the visible light to the near-infrared (NIR) light for single carrier (hole-only or electron-only) SPTs owing to lack of cognitive elements. Herein, 2D perovskite/organic heterojunction (PEA₂SnI₄/Y6) ambipolar SPTs (POASPTs) are developed via solution process. The POASPTs can display dual-mode learning process, which can convert light signals into postsynaptic currents with excitement/inhibition modes (hole-transporting region) or inhibition/excitement (electron-transporting region). The POASPTs exhibit high responsivity to visible light (10⁴ A W⁻¹) and NIR light (200 A W⁻¹), and effectively perform learning and memory simultaneously. The flexible POASPT arrays can successfully recognize the images of different colors of light. This study reveals that the fabricated POASPTs have great potentials in the development of large-area, high-efficiency, and low-cost AIVSs.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Fan Zhang, Shuai Ye, Hanhong Zhang, Feifan Zhou, Yuying Hao, Houzhi Cai, Jun Song, Junle Qu

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Gaopeng Wang, Kai Zhang, Zheng Wang, Jian Wang, Rongguo Xu, Lin Li, Xiuwen Xu, Yu Li, Shuang Xiao, Shizhao Zheng, Xiong Li, Shihe Yang

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.

The strategy of attachable transparent luminescent solar concentrators is proposed. The photoluminescence quantum yield (PLQY) of the red emission perovskite−PVDF composite films is as high as 45.8%. Polystyrene layer is introduced as an antireflection/barrier layer to improve transmittance and suppress PL quenching. A maximum optical efficiency of 2.8% is achieved at the geometric factor of 5.

As large-area photon collection devices designed to convert sunlight into electricity, luminescent solar concentrators (LSCs) have been proposed for more than 40 years. In practical sunlight-harvesting applications, existing glass windows or curtain walls have to be torn down and then replaced by traditional LSCs with planar optical waveguides, leading to high manufacture and installation costs. One alternative and attractive approach is to design and manufacture LSCs that are compatible with and can be attached directly onto the original building glass windows, which substantially reduces the overall costs. Herein, a feasible strategy of attachable transparent LSCs is proposed, converting ordinary glass to LSCs by simply attaching novel luminescent films. By integrating a phenylethylammonium (PEA)-assisted perovskite−PVDF composite film with a polymer antireflection/barrier layer, as-prepared composite films show dramatical improvement in photoluminescence quantum yield from 4.1% to 45.8% (11-fold enhancement), substantially increased optical transmittance from 30.9% to 71.1% (at 700 nm), as well as strongly suppressed photoluminescence (PL) quenching during the attaching process. The fabricated attachable LSCs demonstrate a maximum optical efficiency of 2.8% at the geometric factor of 5 and retain 87% of initial optical efficiency after 2 months of storage in ambient conditions.

Even without defect passivation, the surface recombination of perovskite solar cells can be suppressed by reducing the concentration of minority carriers at the front surface. By introducing a wide-gap perovskite, CsPbBr₃ nanocrystals, to the front surface, the inverted MAPbI₃ cells can achieve significant enhancement of open-circuit voltages without losing photocurrent.

A bandgap gradient at the front surface of solar absorbers can effectively suppress surface recombination while not affecting photocurrent. Herein, it is demonstrated that a front-surface gradient can be formed in an inverted perovskite cell by introducing perovskite quantum dots (QDs) between the hole-transporting layer (HTL) and the remaining absorber. Ultraviolet photoelectron spectroscopy reveals that, with the addition of CsPbBr₃ QDs onto the HTL substrate, the subsequently deposited MAPbI₃ is converted from mild p-type to n-type, and the resultant band alignment can effectively reduce the electron concentration at the front surface without significantly affecting hole extraction. Multiple independent characterizations further confirm the reduction of surface recombination. As a result, the inverted MAPbI₃ cells exhibit an open-circuit voltage of 1.154 V, which translates to a nonradiative recombination loss of 0.15 V and a power conversion efficiency of 20.51%.

Reducing the dimension of the perovskite structure from 3D (MASnI₃) to 2D [(PEA)₂(MA) _{n −1}Sn _n I_{3 n +1} (n = 1, 2, 3, 4)] enables a facile control of carrier concentration and induces the quantum confinement effect. Both the Seebeck coefficient and electrical conductivity increase at an optimum n, which results in a high thermoelectric power factor of 111 µW m⁻¹ K⁻².

Abstract

Organometal halide perovskites (OHPs) exhibit superior charge transport characteristics and ultralow thermal conductivities. However, thermoelectric (TE) applications of OHPs have been limited because of difficulties in controlling their carrier concentration, which is a key to optimizing their TE properties. Here, facile control of the carrier concentration in Sn-based OHPs is achieved by developing 2D crystal structures. The 2D OHP crystals are laterally oriented using a mixed solvent, and the morphology and crystal structure of the coexisting 2D/3D hybrid structures are systematically controlled via doping with methylammonium chloride. The effective number n _eff of inorganic octahedron layers in the 2D OHPs shows a strong positive correlation with the carrier concentration. Moreover, the 2D structure induces the quantum confinement effect, which enhances both the Seebeck coefficient and the electrical conductivity. A 2D OHP shows a high power factor of 111 µW m⁻¹ K⁻², which is an order of magnitude greater than the power factor of its 3D counterpart.

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

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

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.

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.

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.

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.

The >10⁵ discrepancy between recent reports of proton diffusion constants in halide perovskites is analyzed and it is found that the lower value is likely correct. The higher diffusion rate determined from single crystals may be the result of high-diffusivity pathways.

Abstract

A recent report by Cahen and co-workers is examined that finds the diffusion constant for proton migration in methylammonium lead triiodide single crystals to be 2 × 10⁵-fold greater than that previously reported by Sadhu et al. By comparing the conversion of single crystals versus microcrystalline samples, it is concluded that proton diffusion in macroscopic single crystals is accelerated by the presence of defects acting as high-diffusivity paths.

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.

Trigonelline hydrochloride (TH) is selected to modify the SnO₂/perovskite interface. Due to the multifunctional role of TH at the interface, the power conversion efficiency of the device is increased from 19.59% to 21.23%. Moreover, the humidity stability of the non-encapsulated device is also significantly improved after introducing TH to the interface.

Abstract

Interface engineering has been demonstrated to be effective in suppressing the defect-related carrier recombination loss and optimizing the energy level between SnO₂ electron transport layer and mixed-cation perovskite to further improve the performance of perovskite solar cells (PSCs). Herein, a versatile organic salt, trigonelline hydrochloride (TH), is selected to modify the SnO₂/perovskite interface. TH molecule plays a multifunctional role at the interface: (1) COOH and pyridine cation can passivate the interface defects by esterification and electrostatic interaction, respectively. (2) Cl⁻ plays a vital part in the improvement of perovskite crystallization. (3) Dipole effect can move the energy level of SnO₂ resulting in optimized band alignment to more efficient electron extraction. The effects of TH at the interface are revealed by density functional theory calculations, surface chemical analyses, and energy level investigations. As a consequence, the PSCs with TH-modified SnO₂ (SnO₂-TH) exhibit best power conversion efficiency of 21.23%, compared to 19.59% for the reference devices, which mainly results from an enhanced open-circuit voltage (V _oc) from 1.098 V to 1.145 V. Moreover, the humidity stability of the non-encapsulated devices is also significantly improved after introducing TH to the interface.

A series of 8-hydroxyquinoline metal complexes are employed as cathode interfacial layer in inverted planar perovskite solar cells. The introduction of the interfacial layer significantly accelerates the charge transfer and blocks the ion diffusion, leading to better device performance and stability.

Abstract

Ion migration is a crucial factor influencing the stability of perovskite solar cells. Insertion of an interfacial layer between the electron-transporting layer and the cathode is shown to be an effective way to enhance the performance of devices. However, exploring more effective interfacial materials to block ion migration and thus enhance the device stability is still needed. Herein, a series of 8-hydroxyquinoline metal complexes are employed as cathode interfacial layers (CILs) in inverted planar perovskite solar cells. The devices with CILs exhibit better performance, stability, and reproducibility than the control device without CILs. The introduction of the CILs forms a better energy match between the [6,6]-phenyl-C61-butyric acid methyl ester layer and the cathode, reduces the contact resistance, accelerates the charge transfer, and suppresses non-radiative recombination. Moreover, the CILs protect the device from moisture and block the ion diffusions, which is beneficial for device stability. After optimization, the best power conversion efficiency of 20.6% is obtained by using 8-hydroxyquinoline aluminum (Alq₃) as a CIL, and the efficiency remains 85% of its initial value after 800 h continuous illumination.

Interfacial interactions between methylammonium lead iodide (CH₃NH₃PbI₃) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in the presence of humidity lead to the solid state formation and partial incorporation of dimethylammonium, (CH₃)₂NH₂ ⁺, resulting in (CH₃NH₃)_{1− x} [(CH₃)₂NH₂] _x PbI₃. The compositional changes produce a CH₃NH₃ ⁺-rich cubic phase during short-term exposures to high humidity that separates into a (CH₃)₂NH₂ ⁺-rich hexagonal phase during long-term exposures to low humidity.

Abstract

Understanding interfacial reactions that occur between the active layer and charge-transport layers can extend the stability of perovskite solar cells. In this study, the exposure of methylammonium lead iodide (CH₃NH₃PbI₃) thin films prepared on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated glass to 70% relative humidity (R.H.) leads to a perovskite crystal structure change from tetragonal to cubic within 2 days. Interface-sensitive photoluminescence measurements indicate that the structural change originates at the PEDOT:PSS/perovskite interface. During exposure to 30% R.H., the same structural change occurs over a much longer time scale (>200 days), and a reflection consistent with the presence of (CH₃)₂NH₂PbI₃ is detected to coexist with the cubic phase by X-ray diffraction pattern. The authors propose that chemical interactions at the PEDOT:PSS/perovskite interface, facilitated by humidity, promote the formation of dimethylammonium, (CH₃)₂NH₂ ⁺. The partial A-site substitution of CH₃NH₃ ⁺ for (CH₃)₂NH₂ ⁺ to produce a cubic (CH₃NH₃)_{1− x} [(CH₃)₂NH₂] _x PbI₃ phase explains the structural change from tetragonal to cubic during short-term humidity exposure. When (CH₃)₂NH₂ ⁺ content exceeds its solubility limit in the perovskite during longer humidity exposures, a (CH₃)₂NH₂ ⁺-rich, hexagonal phase of (CH₃NH₃)_{1− x} [(CH₃)₂NH₂] _x PbI₃ emerges. These interfacial interactions may have consequences for device stability and performance beyond CH₃NH₃PbI₃ model systems and merit close attention from the perovskite research community.

Conjugated polyelectrolyte is inserted between NiO _x HTLs and perovskite active layer to reduce interfacial Ni²⁺ vacancies trap density. This simultaneously passivates trap-mediated Shockley–Read–Hall recombination and enhances quasi-Fermi level splitting, yielding an increase in open-circuit voltage (V _OC) values to 1.14 V.

Abstract

Nickel oxide (NiO _x ) is desirable hole selective material (HSMs) for perovskite photovoltaics because of the characteristic in stability and low cost. However, they deliver limited open-circuit voltage (V _OC) compared to some organic HSMs. As it is known, the performance of perovskite solar cells is predominantly limited by trap-assisted non-radiative recombination at the perovskite/hole-selective layer interfaces. A typical lithium-doping strategy leads to the valence-band maximum shift and the electronic levels of NiO _x can be tuned robustly to match perovskite active layer in perovskite solar cells. More critically, carrier dynamics studies demonstrate another critical PN4N interlayer strategy reduced interfacial density of defect sites and trap-assisted recombination. These merits contribute coordinately to lower energy loss across the perovskite/NiO _x interface and facilitate charge transport process through the relevant interface, yielding V _OC values increase to 1.14 V and power conversion efficiencies over 20%.