Quantum-Dot Tandem Solar Cells Based on a Solution-Processed Nanoparticle Intermediate Layer

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Colloidal Quantum Dot Solar Cells: Progressive Deposition Techniques and Future Prospects on Large-Area Fabrication

Colloidally grown nanosized semiconductors yield extremely high-quality optoelectronic materials. Many examples have pointed to near perfect photoluminescence quantum yields, allowing for technology-leading materials such as high purity color centers in display technology. Furthermore, because of high chemical yield, and improved understanding of the surfaces, these materials, particularly colloidal quantum dots (QDs) can also be ideal candidates for other optoelectronic applications. Given the urgent necessity toward carbon neutrality, electricity from solar photovoltaics will play a large role in the power generation sector. QDs are developed and shown dramatic improvements over the past 15 years as photoactive materials in photovoltaics with various innovative deposition properties which can lead to exceptionally low-cost and high-performance devices. Once the key issues related to charge transport in optically thick arrays are addressed, QD-based photovoltaic technology can become a better candidate for practical application. In this article, the authors show how the possibilities of different deposition techniques can bring QD-based solar cells to the industrial level and discuss the challenges for perovskite QD solar cells in particular, to achieve large-area fabrication for further advancing technology to solve pivotal energy and environmental issues.

Comprehensive device simulation of 23.36% efficient two-terminal perovskite-PbS CQD tandem solar cell for low-cost applications

The major losses that limit the efficiency of a single-junction solar cell are thermalization loss and transmission loss. Thus, to efficiently utilize the full solar spectrum and to mitigate these losses, tandem solar cells (TSC) have significantly impacted the photovoltaic (PV) landscape. In this context, the research on perovskite/silicon tandems is currently dominating the research community. The stability improvements of perovskite materials and mature fabrication techniques of silicon have underpinned the rapid progress of perovskite/silicon TSC. However, the low absorption coefficient and high module cost of the silicon are the tailbacks for the mass production of perovskite/silicon TSCs. Therefore, PV technology demands to explore some new materials other than Si to be used as absorber layer in the bottom cell. Thus, here in this work, to mitigate the aforementioned losses and to reduce cost, a 23.36% efficient two-terminal perovskite-PbS CQD monolithic tandem solar cell has been designed through comprehensive device simulations. Before analyzing the performance of the proposed TSC, the performance of perovskite top cells has been optimized in terms of variation in optical properties, thickness, and interface defect density under standalone conditions. Thereafter, filtered spectrum and associated integrated filtered power by the top cell at different perovskite thickness from 50 to 500 nm is obtained to conceive the presence of the top cell above the bottom cell with different perovskite thickness. The current matching by concurrently varying the thickness of both the top and bottom subcell has also been done to obtain the maximum deliverable tandem JSC for the device under consideration. The top/bottom subcell with current matched JSC of 16.68 mA cm-2/16.62 mA cm-2 showed the conversion efficiency of 14.60%/9.07% under tandem configuration with an optimized thickness of 143 nm/470 nm, where the top cell is simulated under AM1.5G spectrum, and bottom cell is exposed to the spectrum filtered by 143 nm thick top cell. Further, the voltages at equal current points are added together to generate tandem J-V characteristics. This work concludes a 23.36% efficient perovskite-PbS CQD tandem design with 1.79 V (VOC), 16.67 mA cm-2 (JSC) and 78.3% (FF). The perovskite-PbS CQD tandem device proposed in this work may pave the way for the development of high-efficiency tandem solar cells for low-cost applications.

Design Strategy of Quantum Dot Thin-Film Solar Cells

Quantum dots (QDs) are emerging photovoltaic materials that display exclusive characteristics that can be adjusted through modification of their size and surface chemistry. However, designing a QD-based optoelectronic device requires specialized approaches compared with designing conventional bulk-based solar cells. In this paper, design considerations for QD thin-film solar cells are introduced from two different viewpoints: optics and electrics. The confined energy level of QDs contributes to the adjustment of their band alignment, enabling their absorption characteristics to be adapted to a specific device purpose. However, the materials selected for this energy adjustment can increase the light loss induced by interface reflection. Thus, management of the light path is important for optical QD solar cell design, whereas surface modification is a crucial issue for the electrical design of QD solar cells. QD thin-film solar cell architectures are fabricated as a heterojunction today, and ligand exchange provides suitable doping states and enhanced carrier transfer for the junction. Lastly, the stability issues and methods on QD thin-film solar cells are surveyed. Through these strategies, a QD solar cell study can provide valuable insights for future-oriented solar cell technology.

Enhancing the Efficiency and Stability of PbS Quantum Dot Solar Cells through Engineering an Ultrathin NiO Nanocrystalline Interlayer

Significant progress in PbS quantum dot solar cells has been achieved through designing device architecture, engineering band alignment, and optimizing the surface chemistry of colloidal quantum dots (CQDs). However, developing a highly stable device while maintaining the desirable efficiency is still a challenging issue for these emerging solar cells. In this study, by introducing an ultrathin NiO nanocrystalline interlayer between Au electrodes and the hole-transport layer of the PbS-EDT, the resulting PbS CQD solar cell efficiency is improved from 9.3 to 10.4% because of the improved hole-extraction efficiency. More excitingly, the device stability is significantly enhanced owing to the passivation effect of the robust NiO nanocrystalline interlayer. The solar cells with the NiO nanocrystalline interlayer retain 95 and 97% of the initial efficiency when heated at 80 °C for 120 min and treated with oxygen plasma irradiation for 60 min, respectively. In contrast, the control devices without the NiO nanocrystalline interlayer retain only 75 and 63% of the initial efficiency under the same testing conditions.