Light Management in Organic Photovoltaics Processed in Ambient Conditions Using ZnO Nanowire and Antireflection Layer with Nanocone Array

Proc. Natl. Acad. Sci. U.S.A.

Pò

Bianchi

et al. 2019

Self Cite

Organic photovoltaics (OPVs) have attracted tremendous attention in the field of thin-film solar cells due to their wide range of applications, especially for semitransparent devices. Here, we synthesize a dithiaindacenone-thiophene-benzothiadiazole-thiophene alternating donor copolymer named poly{[2,7-(5,5-didecyl-5H-1,8-dithia-as-indacenone)]-alt-[5,5-(5′,6′-dioctyloxy-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]} (PDTIDTBT), which shows a relatively wide bandgap of 1.82 eV, good mobility, and high transmittance and ambient stability. In this work, we fabricate an OPV device using monolayer graphene as top electrode. Due to the stability of PDTIDTBT in air and water, we use a wet transfer technique for graphene to fabricate semitransparent OPVs. We demonstrate OPVs based on the PDTIDTBT:Phenyl-C61/71-butyric acid methyl ester (PCBM) blend with maximum power conversion efficiencies (PCEs) of 6.1 and 4.75% using silver and graphene top electrodes, respectively. Our graphene-based device shows a high average visible transmittance (AVT) of 55%, indicating the potential of PDTIDTBT for window application and tandem devices. Therefore, we also demonstrate tandem devices using the PDTIDTBT:Phenyl-C61-butyric acid methyl ester (PC60BM) blend in both series and parallel connections with average PCEs of 7.3 and 7.95%, respectively. We also achieve a good average PCE of 8.26% with an average open circuit voltage (Voc) of 1.79 V for 2-terminal tandem OPVs using this blend. Based on tandem design, an OPV with PCE of 6.45% and AVT of 38% is demonstrated. Moreover, our devices show improved shelf life and ultraviolet (UV) stability (using CdSe/ZnS core shell quantum dots [QDs]) in ambient with 45% relative humidity.

mentioning

confidence: 99%

A relatively wide-bandgap and air-stable donor polymer for fabrication of efficient semitransparent and tandem organic photovoltaics

Proc. Natl. Acad. Sci. U.S.A.

Pò

Bianchi

et al. 2019

Self Cite

“…Using experiment and finite‐difference time‐domain simulation, it is discovered that this type of AR layer is wavelength‐independent, and it has a broadband light trapping effect, which can significantly reduce the reflection of a tandem device over the entire solar spectrum. [ 7,41 ]…”

Section: Resultsmentioning

confidence: 99%

“…Organic solar cells (OSCs) have been investigated by many researchers due to their outstanding properties, such as flexibility, semi‐transparency, lightweight, low‐cost processing, and large‐area production. [ 1–7 ] To improve the efficiency of OSCs, several strategies, such as ternary blend, tandem design, new donors, and non‐fullerene acceptors, have been recently developed, [ 8–14 ] where, over the past year, the efficiency of OSCs was increased drastically up to 16.5% for a single junction [ 15 ] and 17.3% for tandem [ 16 ] designs. Among these approaches, tandem OSC has been developed by stacking subcells to improve the absorption of the solar cell in different regions of the solar spectrum.…”

Section: Introductionmentioning

confidence: 99%

Suppression of Photovoltaic Losses in Efficient Tandem Organic Solar Cells (15.2%) with Efficient Transporting Layers and Light Management Approach

Kong

2020

Energy Tech

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Organic solar cells (OSCs) have been investigated by many researchers due to their outstanding properties, such as flexibility, semi-transparency, lightweight, low-cost processing, and large-area production. [1-7] To improve the efficiency of OSCs, several strategies, such as ternary blend, tandem design, new donors, and non-fullerene acceptors, have been recently developed, [8-14] where, over the past year, the efficiency of OSCs was increased drastically up to 16.5% for a single junction [15] and 17.3% for tandem [16] designs. Among these approaches, tandem OSC has been developed by stacking subcells to improve the absorption of the solar cell in different regions of the solar spectrum. [17,18] To design an efficient tandem device, effective approaches, including photon utilization efficiency, bandgap engineering, and interface engineering, need to be considered to minimize the photovoltaic (PV) losses. [19,20] Finding efficient recombination layers and transporting layers is the most effective way to reduce the losses in the tandem device. [21,22] Organic semiconductors have shorter diffusion length as compared with inorganic ones, which results in the recombination of excitons before separation into the free carriers at the interface of donor and acceptor. [23,24] To address this issue, bulk heterojunction OSCs have been developed by blending the donor and acceptor into the active layer. [25-27] Using this concept, the thickness of the absorber layer in OSCs can be increased to over 100 nm, thus improving light absorption. However, the fill factor (FF) of OSCs is often decreased by increasing the thickness of the active layer. In fact, higher shunt resistance (R SH) and lower series resistance (R S) result in improved FF in a solar cell. In an OSC device, R SH and R S are influenced by variation of recombination in the active layer, where R SH is enhanced by reducing the monomolecular recombination (recombination of a bound geminate holeelectron pair before converting to the mobile carriers), and R S is reduced by an increase in bimolecular recombination (recombination of mobile holes and electrons at acceptor/donor interface). [28,29] In a tandem OSC, the active layers in both subcells are thinner than a normal cell, and thus, the recombination will be reduced, leading to a higher FF. [30] In this regard, Liu et al. [31] reported a tandem OSC with a high FF of 77% and a PCE of 14%, using similar active layers in both subcells and tuning their thicknesses. In fact, fabrication of a tandem device can be a good solution to not only enhance the open circuit voltage and PCE of the OSCs, but also improve the light stability of the top cell OSC (where the active layer has lower bandgap) due to the filtering of high energy photons by the bottom cell. Interface engineering using efficient transporting and recombination layers in a tandem OSC is a great strategy to minimize

“…[27][28][29][30] In fact, finding new effective transporting layers for the PSCs is a good strategy to address this issue. [31][32][33] Titanium dioxide (TiO 2 ) is one of the most commonly used electron transporting layers (ETLs) in the PSCs. [13,34,35] However, it suffers from hysteresis and stability issues due to having high amount of oxygen vacancies caused by UV light and also weak charge extraction properties.…”

mentioning

confidence: 99%

Efficient Perovskite Solar Cells Based on CdSe/ZnS Quantum Dots Electron Transporting Layer with Superior UV Stability

Physica Rapid Research Ltrs

Prochowicz

Yadav

et al. 2020

Self Cite

Organic-inorganic perovskite materials with their outstanding optoelectronic properties have made a revolution in the field of optoelectronic devices. [1][2][3][4][5][6][7][8] Among all thin film photovoltaics (PVs), perovskite solar cells (PSCs) show a fast progress in a short period of time with high efficiency exceeding 25%, due to their great absorption, long diffusion length, high-quality crystals, low cost, and low-temperature processing. [9][10][11][12][13][14] Over the past years, researchers mostly focused on compositional engineering, interface engineering, additive engineering, and surface passivation approaches to boost the device performance as well as stability. [15][16][17][18][19][20][21][22][23][24][25][26] Apart from extensive efforts of researchers in this regard, stability is still the main challenge in this field. [27][28][29][30] In fact, finding new effective transporting layers for the PSCs is a good strategy to address this issue. [31][32][33] Titanium dioxide (TiO 2 ) is one of the most commonly used electron transporting layers (ETLs) in the PSCs. [13,34,35] However, it suffers from hysteresis and stability issues due to having high amount of oxygen vacancies caused by UV light and also weak charge extraction properties. [36] To address this shortening, double-layer ETL and doping strategy have been proposed by many groups, which can improve slightly the efficiency and stability. [37][38][39] Moreover, employment of new organic and inorganic ETLs such as tin oxide (SnO 2 ) with better transporting properties could be another solution for this issue. [40] However, these strategies cannot protect the PSCs from the UV illumination. Applying downshifting materials on the PSCs is an effective way for this purpose. [41,42] In this study, we propose CdSe/ZnS QDs as a new ETL in the planar PSCs for the first time, with downshifting property. We fabricate methylammonium lead triiodide (MAPbI 3 ) perovskite on a thin layer of CdSe/ZnS QDs ETL using evaporation technique. We find that the PSC on CdSe/ZnS QDs ETL with green emission gives us the best efficiency due to more suitable band alignment with respect to the perovskite film than the dots with red emission. We finally achieve a PSC with 18% PCE, indicating a superior UV stability and low hysteresis.Here, we considered CdSe/ZnS QDs (Mesolight) with green (520 nm) and red (640 nm) emissions at ETLs in the PSCs, which have photoluminescence quantum efficiencies (PLQEs) of 85% ( Figure S1, Supporting Information). Here, we used CdSe QDs wrapped by ZnS shell due to having higher PLQE and better downshifting property as compared with the pure QDs layers. [43] The PLQE has an important role in the efficiency of the device and if it is not high enough, the QDs layer cannot efficiently convert the photons with high energy to the photons with low energy, resulting in lower current density and thus PCE. In this work, we used a solid-state ligand exchange method for deposition of the QDs layer. Then, we used methylammonium triiodide (MAPbI 3 ) perovskit...