Jialong Duan

Recent advances in critical materials for quantum dot-sensitized solar cells: a review

Quantum dot-sensitized solar cells (QDSCs) present promising cost-effective alternatives to conventional silicon solar cells due to their distinctive properties such as simplicity in fabrication, possibility to realize light absorption in wide solar spectrum regions, and theoretical conversion efficiency up to 44%. This review highlights recent developments in critical materials including quantum dots, photoanodes, counter electrodes (CEs), and electrolytes for QDSC applications. Among them, electron recombination at the photoanode/electrolyte interface limits the evolution of high-efficiency QDSCs, therefore the optimized construction of quantum dots, the various microtopographies of wide bandgap semiconductors (TiO2, ZnO) as well as emerging CEs having good electrocatalytic activity are elaborated in this paper. We argue that these key factors can provide design guidelines for future successful applications and significantly promote the development of QDSCs. Liquid, quasi-solid-state, and solid-state electrolytes for QDSCs are summarized, aiming at enhancing the long-term stability of QDSCs. This review presented below gives a succinct summary of materials for QDSC applications, with a conclusion and future prospects section.

Efficient quasi-solid-state dye-sensitized solar cells from graphene incorporated conducting gel electrolytes

Aimed at enhancing the liquid electrolyte loading, ionic conductivity, and electrocatalytic activity toward iodides, a freeze-dried microporous polyacrylate–poly(ethylene glycol) (PAA–PEG) matrix was employed to uptake conducting substances, such as graphene, graphene oxide, and graphite. A liquid electrolyte loading of 21.1 g per g and a room-temperature ionic conductivity of 11.60 mS cm−1 were obtained from the PAA–PEG/graphene conducting gel electrolyte. The conducting substances can form interconnected channels within the insulating microporous PAA–PEG matrix, therefore, the reduction reaction of triiodide ions in the dye-sensitized solar cells (DSSCs) can be extended from the Pt/gel electrolyte interface to both the interface and three-dimensional framework of the microporous conducting gel electrolyte. The resulting DSSCs made from PAA–PEG/graphene, PAA–PEG/graphene oxide, and PAA–PEG/graphite exhibit power conversion efficiencies of 7.74%, 6.49%, and 5.63%, respectively, which are much higher than 5.02% exhibited by a pure PAA–PEG-based DSSC. This new concept, along with ease of fabrication suggests that microporous conducting gel electrolytes could be good alternative electrolytes for use in efficient quasi-solid-state DSSCs.

High‐Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency

All-inorganic perovskite solar cells with high efficiency and improved stability are promising for commercialization. A multistep solution-processing method was developed to fabricate high-purity inorganic CsPbBr3 perovskite films for use in efficient solar cells. By tuning the number of deposition cycles (n) of a CsBr solution, the phase conversion from CsPb2 Br5 (n ≤3), to CsPbBr3 (n=4), and Cs4 PbBr6 (n≥5) was optimized to achieve vertical- and monolayer-aligned grains. Upon interfacial modification with graphene quantum dots, the all-inorganic perovskite solar cell (without a hole-transporting layer) achieved a power conversion efficiency (PCE) as high as 9.72 % under standard solar illumination conditions. Under challenging conditions, such as 90 % relative humidity (RH) at 25 °C or 80 °C at zero humidity, the optimized device retained 87 % PCE over 130 days or 95 % over 40 days, compared to the initial efficiency.

Solid-state electrolytes from polysulfide integrated polyvinylpyrrolidone for quantum dot-sensitized solar cells

Solid-state electrolytes from S2−/Sn2− integrated polyvinylpyrrolidone (PVP) are synthesized by a simple blending method. The ionic conductivity, charge-transfer ability, and therefore photovoltaic performances are optimized by adjusting the Na2S/S stoichiometric ratio. The quantum dot-sensitized solar cell (QDSSC) is assembled by sandwiching the solid electrolyte between a CdS-sensitized TiO2 anode and a CoSe alloy counter electrode. An optimal efficiency of 0.55% is measured for the QDSSC employing PVP/10Na2S–S solid electrolyte. The present work demonstrates the feasibility of designing cost-effective solid-state electrolytes with PVP, and the photovoltaic performances of QDSSCs can be further elevated by optimizing the synthesis conditions.

All-solid-state quantum dot-sensitized solar cell from plastic crystal electrolyte

A plastic crystal based solid-state electrolyte composing of plastic crystal succinonitrile and sodium sulfide (Na2S) is creatively synthesized by a simple blending approach. The ionic conductivity, charge-transfer ability, and photovoltaic performance are optimized by adjusting the succinonitrile/Na2S ratio. An optimal power conversion efficiency of 1.29% is measured for its quantum dot-sensitized solar cell (QDSSC) under one sun irradiation. The impressive efficiency along with the simple preparation of the cost-effective Na2S integrated succinonitrile electrolytes highlights the potential application of plastic crystal electrolytes in solid-state QDSSCs.

Simplified Perovskite Solar Cell with 4.1% Efficiency Employing Inorganic CsPbBr3 as Light Absorber

Perovskite solar cells with cost-effectiveness, high power conversion efficiency, and improved stability are promising solutions to the energy crisis and environmental pollution. However, a wide-bandgap inorganic-semiconductor electron-transporting layer such as TiO2 can harvest ultraviolet light to photodegrade perovskite halides, and the high cost of a state-of-the-art hole-transporting layer is an economic burden for commercialization. Here, the building of a simplified cesium lead bromide (CsPbBr3 ) perovskite solar cell with fluorine-doped tin oxide (FTO)/CsPbBr3 /carbon architecture by a multistep solution-processed deposition technology is demonstrated, achieving an efficiency as high as 4.1% and improved stability upon interfacial modification by graphene quantum dots and CsPbBrI2 quantum dots. This work provides new opportunities of building next-generation solar cells with significantly simplified processes and reduced production costs.

Interfacial engineering of hybridized solar cells for simultaneously harvesting solar and rain energies

Photovoltaics have been regarded as a promising solution to energy and environmental problems, however the state-of-the-art photovoltaics cannot harvest energy or therefore generate electricity in completely dark conditions. To address this issue, we present here the realization of physical proof-of-concept hybridized solar cells by tailoring photovoltaics with polyaniline and its derivates for harvesting energy from the sun and rain. Through interfacial engineering, the optimized polyaniline–graphene/PtCo tailored solar cell yields a photo efficiency of 9.09% under air mass 1.5 illumination and a dark efficiency of up to 25.58% as well as current and voltage under the stimulus of real rain. This work may enable scientists to explore advanced all-weather solar cells revolutionizing photovoltaics.

Toward charge extraction in all-inorganic perovskite solar cells by interfacial engineering

All-inorganic perovskite solar cells (PSCs) are a promising solution to address the poor stability of organic–inorganic hybrid PSC devices under humidity and thermal attacks. However, the severe interfacial charge recombination from large energy differences has markedly limited the further enhancement of power conversion efficiency. The charge extraction from perovskite layer has been improved by setting intermediate energy levels using quantum dots (QDs) through interfacial engineering. In the current study, CuInS2/ZnS QDs with tunable bandgaps and hole-transporting behavior were prepared to modify the CsPbBr3/carbon interface. Arising from the improved charge separation, a power conversion efficiency of 8.42% was achieved for QD tailored inorganic PSC in comparison with 6.01% for pristine devices. These all-inorganic PSCs present unprecedented stability under high humidity and significant improvements in the fill factor, short-circuit photocurrent, and open-circuit voltage.

Alloy-Controlled Work Function for Enhanced Charge Extraction in All-Inorganic CsPbBr3 Perovskite Solar Cells

All-inorganic CsPbX3 (X=I, Br) perovskite solar cells are regarded as cost-effective and stable alternatives for next-generation photovoltaics. However, sluggish charge extraction at CsPbX3 /charge-transporting material interfaces, which arises from large interfacial energy differences, have markedly limited the further enhancement of solar cell performance. In this work, the work function (WF) of the back electrode is tuned by doping alloyed PtNi nanowires in carbon ink to promote hole extraction from CsPbBr3 halides, while an intermediate energy by setting carbon quantum dots (CQDs) at TiO2 /CsPbBr3 interface bridges electron transportation. The preliminary results demonstrate that the matching WFs and intermediate energy level markedly reduce charge recombination. A power conversion efficiency of 7.17 % is achieved for the WF-tuned all-inorganic perovskite solar cell, in comparison with 6.10 % for the pristine device, and this is further increased to 7.86 % by simultaneously modifying with CQDs. The high efficiency and improved stability make WF-controlled all-inorganic perovskite solar cells promising to develop advanced photovoltaic platforms.