Chen Weijie

A hybrid nanocomposite of PbSe colloidal quantum dots blended with CsPbBr_1.5I_1.5 nanocrystals is integrated for photodetectors ITO/ZnO/PbSe:CsPbBr_1.5I_1.5/P3HT/Au. As a result, a photoresponsivity of 6.16 A W⁻¹ with a specific detectivity of 5.96 × 10¹³ Jones and an ON/OFF current ratio of 10⁵ is obtained in self-powered mode. Also, the device performance is simulated with Technology Computer-Aided Design software, and the physical mechanisms are discussed in detail.

Abstract

Self-powered broadband photodetectors exhibit excellent self-powered and wide-band photoresponse from visible to infrared region and attract enormous attention due to their promising applications in imaging, sensing, and optical communication. PbSe colloidal quantum dots (CQDs) and halide perovskites nanocrystals (NCs) are commonly used for photodetectors due to their strong absorption capability, tunable bandgap, and high aspect ratio. However, due to suffering from low charge carrier mobility and high trap density, the performance of individual PbSe CQDs and perovskites-based photodetectors is not satisfactory. Integration of PbSe CQDs with inorganic mixed-halide perovskite nanomaterials can provide an opportunity to overcome these drawbacks. In this work, a hybrid nanocomposite of PbSe CQDs blended with all-inorganic mixed halide perovskite NCs is integrated to fabricate bulk-heterojunction-based high-performance photodetectors. The transportation of photogenerated carriers is enhanced by employing electrons- and holes-extracting layers. As a result, the photoresponsivity of 6.16 A W⁻¹ and a specific detectivity of 5.96 × 10¹³ Jones with an ON/OFF current ratio of 10⁵ is obtained for bulk-heterojunction photodetector ITO/ZnO/PbSe:CsPbBr_1.5I_1.5/P3HT/Au in the self-powered mode. Meanwhile, the device performance of the fabricated photodetector is numerically simulated by using Technology Computer-Aided Design software, and the physical mechanisms for photogenerated carriers’ transportation are discussed in detail.

Publication date: July 2022

Source: Nano Energy, Volume 98

Author(s): Tonghui Guo, Huayang Wang, Wenhua Han, Jing Zhang, Changlei Wang, Tianshu Ma, Zequn Zhang, Zhiqiang Deng, Da Chen, Wenwu Xu, Xiaohui Liu, Like Huang, Ziyang Hu, Yuejin Zhu

A dual-function of crosslinking and chelating strategy is established to dramatically eliminate the defects and enhance the long-term stability of perovskite solar cells (PerSCs) via a crosslinkable organic ligand (C1). Though chemical anchoring and in situ crosslinking of C1, electrode interfaces, and perovskite grains are collaboratively optimized, resulting in highly efficient and stable PerSCs.

Abstract

The organic–inorganic halide perovskite solar cell (PerSC) is the state-of-the-art emerging photovoltaic technology. However, the environmental water/moisture and temperature-induced intrinsic degradation and phase transition of perovskite greatly retard the commercialization process. Herein, a dual-functional organic ligand, 4,7-bis((4-vinylbenzyl)oxy)-1,10-phenanthroline (namely, C1), with crosslinkable styrene side-chains and chelatable phenanthroline backbone, synthesized via a cost-effective Williamson reaction, is introduced for collaborative electrode interface and perovskite grain boundaries (GBs) engineering. C1 can chemically chelate with Sn⁴⁺ in the SnO₂ electron transport layer and Pb²⁺ in the perovskite layer via coordination bonds, suppressing nonradiative recombination caused by traps/defects existing at the interface and GBs. Meanwhile, C1 enables in situ crosslinking via thermal-initiated polymerization to form a hydrophobic and stable polymer network, freezing perovskite morphology, and resisting moisture degradation. Consequently, through collaborative interface-grain engineering, the resulting PerSCs demonstrate high power conversion efficiency of 24.31% with excellent water/moisture and thermal stability. The findings provide new insights of collaborative interface-grain engineering via a crosslinkable and chelatable organic ligand for achieving efficient and stable PerSCs.

A fluid mechanics inspired reversible and sequential layer-by-layer (RS-LBL) deposition method is developed, which provides a high-performance 36 cm² OSC module with uniform mass (donor and/or acceptor component)/phase distribution of blends in large-scale blade-coating. As a result, a record PCE of 13.47% is achieved for binary solar modules with an active area over 30 cm².

Abstract

Despite rapid advances in the field of organic solar cells (OSCs), high-performance large-scale OSC modules are limited. In this study, it is found that the non-Newtonian fluid feature of conjugated polymer primarily causes the wedge-shaped mass (donor and/or acceptor component)/phase distribution of blends in large-scale blade coating, which results in the lower module efficiency. To address the critical issue in printing manufacturing, a reversible and sequential layer-by-layer (RS-LBL) deposition method with sequential twice forward/reverse blade-coating of polymer donor and forward blade-coating of Y6 acceptor, is developed for precisely controlling fluid mechanics of PM6:Y6 active layer. Through using the RS-LBL strategy, uniform morphology and favorable phase separation and crystallization are obtained in the 10 × 10 cm² active layer. As a result, the RS-LBL-based OSCs show excellent operational stability, and an outstanding PCE of 13.47% is achieved with significantly suppressed charge recombination losses in the 36 cm² large-area OSC module, which represents the highest efficiency of binary solar modules with the area over 30 cm². This study provides a feasible route for the next generation of high-performance large-area OSCs and OSC modules.

CsPbI₃ solutions enriched with europium precursors are infiltrated into stacks of mesoporous (mp) materials (mp-TiO₂/mp-ZrO₂/mp-Carbon) to fabricate mesoscopic carbon-based perovskite solar cells (mC-PSCs). The use of europium mitigates γ-to-δ phase transition and lattice defect formation, allowing to achieve a photon-to-current efficiency of 9.2% using EuI₂. The mC-PSC recycling is feasible by exploiting the special feature of the high-temperature black γ-phase-reversibility.

CsPbI₃ perovskites are attracting huge interest for their inorganic structure and thanks to a bandgap of 1.69–1.78 eV that makes them suitable for application in tandem solar cells with silicon. Herein, all-inorganic hole-transporting-layer (HTL)-free carbon-based CsPbI₃ perovskite solar cells (mC-PSCs) are fabricated, for the first time, by infiltrating CsPbI₃ solutions enriched with precursors of Europium into triple mesoscopic structures with mesoporous (mp) materials (mp-TiO₂/mp-ZrO₂/mp-Carbon). The use of Europium is beneficial to mitigate lattice defect formation during the reaction. Drop casting of the solution is done in air and the black γ-phase formation is promoted under dynamic nitrogen flow during high-temperature annealing (350 °C), which is preferred to low-temperature treatments to maximize perovskite phase stability. The preparation protocol entrusts the devices with the best power conversion efficiencies (PCEs) of 9.2% and 5.2% using EuI₂ and EuCl₃, respectively. Recorded PCE is considerably lower (<2%) in the reference devices prepared without Europium. In addition, the Eu-based devices are recycled to reconvert the photo-inactive yellow δ-phase into the photo-active black γ-phase with the devices losing only ≈10% of the efficiency of the original device. Thus, it is demonstrated that mC-PSCs recycling is feasible by exploiting the special feature of the high-temperature black γ-phase-reversibility.

A reversible degradation phenomenon is observed in the hole transport layer-free carbon-based perovskite solar cells, which is chemically revealed to be derived from the reversible reaction of monohydrate at the interface of perovskite/carbon electrode.

The rationale for ambient degradation behaviors in hole transport layer (HTL)-free carbon-based perovskite solar cells (PSCs) still remains a mystery, although carbon-based PSCs have been the frontrunner among the emerging next-generation photovoltaics owing to their low cost of materials and fabrication process, as well as the exceptional durability. Herein, the long-term stability of HTL-free carbon-based PSCs (H-C-PSCs) in the ambient air environment is investigated to thoroughly understand and identify the governing chemistry during the degradation. Specifically, a reversible degradation phenomenon is observed along with an anomalous S-shape of current–voltage curves involving only reduction of fill factor (FF), almost without impact for short-circuit current density and open-circuit voltage. Furthermore, a minute-heating treatment will eliminate the reversible degradation which can be attributed to the reversible formation of intermediate hydrate at the interface between perovskite and carbon contact. This provides a new perspective for the stability issue of H-C-PSCs.

Publication date: July 2022

Source: Nano Energy, Volume 98

Author(s): Siwei Luo, Fujin Bai, Jianquan Zhang, Heng Zhao, Indunil Angunawela, Xinhui Zou, Xiaojun Li, Zhenghui Luo, Kui Feng, Han Yu, Kam Sing Wong, Harald Ade, Wei Ma, He Yan

Publication date: 18 May 2022

Source: Joule, Volume 6, Issue 5

Author(s): Minhuan Wang, Yepin Zhao, Xiaoqing Jiang, Yanfeng Yin, Ilhan Yavuz, Pengchen Zhu, Anni Zhang, Gill Sang Han, Hyun Suk Jung, Yifan Zhou, Wenxin Yang, Jiming Bian, Shengye Jin, Jin-Wook Lee, Yang Yang

A highly crystalline small molecule BTR-Cl is introduced into the PM6:Y6 host blend to optimize the crystallization behavior and more suitable vertical phase distribution. Power conversion efficiency is maintained over 15% with an active layer thickness of 300 nm. This provides a larger variable thickness window to increase the reproducibility and compatiblity with the roll-to-roll process for large-scale printing techniques.

Abstract

Thick film organic solar cells have great potential for preparing large-area devices in the future. However, unsuitable vertical donor/acceptor distribution, poor crystallinity of materials, and voltage losses remain unclear, limiting the performance of thick film devices. Here, a target ternary strategy by introducing a nematic liquid crystalline small molecule donor BTR-Cl into the PM6:Y6 host system is used to reduce the performance degradation caused by the increase of active layer thickness. By incorporating 10% BTR-Cl into the blend film, the voltage loss is minimized in both thin and thick ternary devices. Moreover, the power conversion efficiency of the ternary device is maintained at 15.28% compared to 12.94% of binary devices with an active layer thickness of 300 nm. It is benefited from the optimized crystallization behavior and more suitable vertical phase distribution driven by differences in miscibility between components. While ensuring sufficient phase separation, the charge transport is improved, it also prompts the balance of charge transport and reduces the non-radiative recombination. This work demonstrates that the use of the third component to enhance the crystallization of the active layer and improve the vertical phase distribution is an effective method to build thick films for future large-scale printing techniques.

A vacuum-assisted thermal annealing approach is employed for the fabrication of CsPbI₃ perovskite films with full surface coverage and enhanced crystallization. The resultant CsPbI₃ perovskite solar cells exhibit a power conversion efficiency (PCE) as high as 20.06 %, along with enhanced long-term stability.

Abstract

Inorganic cesium lead iodide perovskite CsPbI₃ is attracting great attention as a light absorber for single or multi-junction photovoltaics due to its outstanding thermal stability and proper band gap. However, the device performance of CsPbI₃-based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non-radiative recombination. Here, vacuum-assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI₃ perovskite films formed from the precursors of PbI₂, CsI, and dimethylammonium iodide (DMAI). By this method, a large-area and high-quality CsPbI₃ film is obtained, exhibiting a much reduced trap-state density with prolonged charge lifetime. Consequently, the solar cell efficiency is raised from 17.26 to 20.06 %, along with enhanced stability. The VATA would be an effective approach for fabricating high-performance thin-film CsPbI₃ perovskite optoelectronics.

Fabrication of effective inorganic hole transport films at low temperature is crucial to move perovskite solar cells one step closer to mass production and then commercialization. Here, the authors report a photochemistry method to synthesize NiO_x hole transport layer for perovskite solar cells with a champion performance of 22.45%.

Abstract

High crystallization and conductivity are always required for inorganic carrier transport materials for cheap and high-performance inverted perovskite solar cells (PSCs). High temperature and external doping are inevitably introduced and thus greatly hamper the applications of inorganic materials for mass production of flexible and tandem devices. Here, an amorphous and dopant-free inorganic material, Ni³⁺-rich NiO_x, is reported to be fabricated by a novel UV irradiation strategy, which is facile, easily scaled-up, and energy-saving because all the processing temperatures are below 82 ℃. The as-prepared NiO_x film shows highly improved conductivity and hole extraction ability. The rigid and flexible PSCs present the champion efficiencies of 22.45% and 19.7%, respectively. This work fills the gap of preparing metal oxide films at the temperature below 150 °C for inverted PSCs with the high efficiency of >22%. More importantly, this work upgrades the substantial understanding about inorganic materials to function well as efficient carrier transport layers without external doping and high crystallization.

A power conversion efficiency (PCE) of 12.58% and an average visible transmittance (AVT) of 22.81% are achieved in semitransparent layer-by-layer (LbL) organic photovoltaics (OPVs) with D18/N3 as active layers. This work demonstrates that the strategy by adjusting donor layer thickness may be an efficient method to construct efficient semitransparent LbL-OPVs.

Layer-by-layer organic photovoltaics (LbL-OPVs) are fabricated using wide bandgap polymer D18 with narrow photon harvesting range in visible light region and narrow bandgap small molecular N3 with strong near-infrared photon harvesting; the only difference is D18 layer thickness adjusted by spin coating speed. A 15.75% power conversion efficiency (PCE) is obtained from the LbL-OPVs with D18 layer prepared under 7000 round per minute of spin coating condition; the corresponding D18/N3 layers have a 52.06% of average visible transmittance (AVT) in the spectral range from 370 to 740 nm. Based on the optimized D18/N3 layers, semitransparent LbL-OPVs are built with 1 nm Au/(10, 15, 20 nm) Ag as the top electrode. The PCE and AVT of semitransparent LbL-OPVs can be simultaneously adjusted by altering Ag layer thickness due to its variable reflectance and conductivity of top electrode dependence on Ag layer thickness. The PCE/AVT of 12.58%/22.81%, 13.80%/15.09%, and 14.85%/9.48% can be individually achieved from the semitransparent LbL-OPVs with 10, 15, or 20 nm-thick Ag layer, which should be among the highest values of semitransparent OPVs based on bulk heterojunction or LbL structures. Adjusting donor layer thickness may be an effective method to construct efficient semitransparent LbL-OPVs.