While nanocrystals in group II-IV semiconductors have been extensively studied as photosensitizers in quantum dot-sensitized solar cells (QDSCs), their practical use is severely hampered by the high toxicity of the heavy metals, like Cd, Pb, and Hg, present in these semiconductors. Our present work is based on a proposition to use a “green” alternative to the currently used sensitizers, namely CuInS2 which is a low-toxic semiconductor. However, as for many other types of QDs, surface defects limit also their photovoltaic performance. Therefore, in order to passivate the surface defects and improve the performance of CuInS2 QDs we explore in this work two strategies-ZnS shell coating and hybrid passivation. The results show that although ZnS shell coating can effectively passivate the surface defects, the electron injection from QDs to TiO2 nanoparticle is also hampered. Moreover, the size of CuInS2 QDs is increased after the shell coating, which also is unfavorable for the enhancement of the solar cells efficiency. In contrast, hybrid passivation can passivate the surface defects on the CuInS2 QDs without size changing, and can increase the loading efficiency of the QDs simultaneously. Consequently, the efficiency of the solar cells is improved to 4.7%, which is a promising result for the green CuInS2 based QDSCs. Therefore, in addition to the most used shell coatings of CuInS2 QDs, hybrid passivation may be an effective way for improving their photovoltaic performance. This study employs two strategies “hybrid passivation and ZnS shell coating” and discuss about their effect in solar cell efficiency.

Hole-transporting material (HTM) plays a paramount role in enhancing the photovltaic performance of perovskite solar cells (PSCs). Currently, the vast majority of these HTMs employed in PSCs are organic small molecules and polymers, yet the use of organic metal complexes in PSCs applications remains less explored. To date, most of reported HTMs require additional chemical additives (e.g. Li-TFSI, t-TBP) towards high performance, however, the introduction of additives decrease the PSCs device stability. Herein, an organic metal complex (Ni-TPA) is first developed as a dopant-free HTM applied in PSCs for its facile synthesis and efficient hole extract/transfer ability. Consequently, the dopant-free Ni-TPAbased device achieves a champion efficiency of 17.89%, which is superior to that of pristine SpiroOMeTAD (14.25%). Furthermore, we introduce a double HTM layer with a graded energy bandgap containing a Ni-TPA layer and a CuSCN layer into PSCs, the non-encapsulated PSCs based on the Ni-TPA/ CuSCN layers affords impressive efficiency up to 20.39% and maintains 96% of the initial PCE after 1000 h at a relative humidity around 40%. The results have demonstrated that metal organic complexes represent a great promise for designing new dopant-free HTMs towards highly stable PSCs.

A concept of transparent “quantum dot glass”(TQDG) is proposed for a combination of a quantum dot(QD)-based glass luminescent solar concentrator (LSC) and itsedge-attached solar cells, as a type of transparent photovoltaics(TPVs) for building-integrated photovoltaics (BIPVs). Differentfrom conventional LSCs, which typically serve as pure opticaldevices, TQDGs have to fulfill requirements as both powergeneratingcomponents and building construction materials. In thiswork, we demonstrate large-area (400 cm2) TQDGs based onsilicon QDs in a triplex glass configuration. An overall powerconversion efficiency (PCE) of 1.57% was obtained with back-reflection for a transparent TQDG (average visible transmittance of84% with a color rendering index of 88 and a low haze ≤3%), contributing to a light utilization efficiency (LUE) of 1.3%, which isamong the top reported TPVs based on the LSC technology with similar size. Most importantly, these TQDGs are shown to havebetter thermal and sound insulation properties compared to normal float glass, as well as improved mechanical performance andsafety, which significantly pushes the TPV technology toward practical building integration. TQDGs simultaneously exhibit favorablephotovoltaic, aesthetic, and building envelope characteristics and can serve as a multifunctional material for the realization of nearlyzero-energy building concepts.

This letter introduces a novel approach estimating the power conversion efficiency (PCE) of a square luminescent solar concentrator (LSC) by point excitations on the “optical centers” as proposed here. Predicted by theoretical calculations, photoluminescence emissions from these optical centers experience almost the same average optical path with those from the whole device under uniform illumination. This is experimentally verified by a 20 × 20 cm2 silicon quantum dots-based LSC, with a negligible error between the predicted PCE and the measured one. This method provides a convenient way to estimate the photovoltaic performance of large-area LSC devices with basic laboratory instruments.

Electron transport layer (ETL)/perovskite interface passivation is particularly challenging because of the use of polar solvents (e.g., DMF) for perovskite solution deposition, which usually destroy the bottom as-formed defect passivation layers. Herein, a novel multi-functional composite ETL, NH2-ZnO@SnO2, is prepared by mixing amino-capped ZnO (NH2-ZnO) nanocrystals (NCs) with SnO2 nanoparticles. The best-performing PSCs on the basis of NH2-ZnO@SnO2 achieve efficiency of 22.52%, which is significantly higher than that of the pristine SnO2 counterpart (18.45%) The enhanced performance of the NH2-ZnO@SnO2 ETL can be attributed to higher electron extraction capacity, better energy-level alignment with perovskite material, and more efficient carrier transport in device. Most important, the NH2 groups on the surface of ZnO NCs can effectively passivate the under-coordinated Pb2+ ions from perovskite films, thus reducing charge recombination at ETL/perovskite interface. The results suggest that NH2-ZnO NCs@SnO2 composite is a promising ETL for improving the performance of PSCs.

As a cost-effective batch synthesis method, Si quantum dots (QDs) with nearinfrared photoluminescence, high quantum yield (>50% in polymer nanocomposite), and nearunity internal quantum efficiency were fabricated from an inexpensive commercial precursor (triethoxysilane, TES), using optimized annealing and etching processes. The optical properties of such QDs are similar to those prepared from state-of-the-art precursors (hydrogen silsesquioxane, HSQ) yet featuring an order of magnitude lower cost. To understand the effect of synthesis parameters on QD optical properties, we conducted a thorough comparison study between common solid precursors: TES, HSQ, and silicon monoxide (SiO), including chemical, structural, and optical characterizations. We found that the structural nonuniformity and abundance of oxide inherent to SiO limited the resultant QD performance, while for TES-derived QDs this drawback can be avoided. The presented low-cost synthetic approach would significantly favor applications requiring high loading of good-quality Si QDs, such as light conversion for photovoltaics.

Luminescent solar concentrator (LSC) is a promising technology to integrate semitransparent photovoltaic (PV) systems into modern buildings and vehicles. Silicon quantum dots (QDs) are good candidates as fluorophores in LSCs, due to the absence of overlap between absorption and emission spectra, high photoluminescence quantum yield (PLQY), good stability, nontoxicity, and element abundance. Herein, LSCs based on Si QDs/polymer nanocomposites are fabricated in a triplex glass configuration. A special polymer matrix (off-stoichiometric thiol-ene, OSTE) is used, which improves Si nanocrystal quantum yield. Herein, a comprehensive investigation to improve the performance of LSCs by exploring different strategies under the guidance of a theoretical description is conducted. Among these strategies, the systematical enhancement of PLQY of the nanocomposite is achieved by tuning the thiol/allyl group ratio in the OSTE matrix. In addition, ligand selection and loading optimization for QDs reduce the total scattering loss in the device. Finally, an optical power efficiency of 7.9% is achieved for an optimized LSC prototype (9 x 9 x 0.6 cm(3), transmittance approximate to 62% at 500 nm) based on Si QDs/OSTE nanocomposite, which shows good potential of this material system in LSC fabrication.

Heavy metal-free CuInS2 quantum dots (QDs) were employed as a photosensitizer on a NiO photocathode to drive an immobilized molecular Re catalyst for photoelectrochemical CO2 reduction for the first time. A photocurrent of 25 mu A cm(-2) at -0.87 V vs. NHE was obtained, providing a faradaic efficiency of 32% for CO production.

Type-II Cu2GeS3/InP core/shell quantum dots (QDs) are designed using density functional theory and synthesized by a hot injection method in order to enhance the power conversion efficiency of quantum dot sensitized solar cells. The low toxicity and an absorption extending to the infrared region are key aspects of the importance of these QDs. The longer absorption achieved for type-II Cu2GeS3/InP QDs compared to single core Cu2GeS3 QDs is achieved by optimization of the band alignment. This leads to a more efficient carrier separation and a suppression of the electron-hole recombination. The results show that the efficiency and the electron injection rate constant increase by more than 5 and 2 times, respectively.

Ternary alloy PbxCd1-xS quantum dots (QDs) were explored as photosensitizers for quantum-dot-sensitized solar cells (QDSCs). Alloy PbxCd1-xS QDs (Pb0.54Cd0.46S, Pb0.31Cd0.69S, and Pb0.24Cd0.76S) were found to substantially improve the photocurrent of the solar cells compared to the single CdS or PbS QDs. Moreover, it was found that the photocurrent increases and the photovoltage decreases when the ratio of Pb in PbxCd1-xS is increased. Without surface protecting layer deposition, the highest short-circuit current density reaches 20 mA/cm(2) under simulated AM 1.5 illumination (100 mW/cm(2)). After an additional CdS coating layer was deposited onto the PbxCd1-xS electrode, the photovoltaic performance further improved, with a photocurrent of 22.6 mA/cm(2) and an efficiency of 3.2%.