Efficient Hole Transporting Materials with Two or Four N,N‐Di(4‐methoxyphenyl)aminophenyl Arms on an Ethene Unit for Perovskite Solar Cells

Novel steric bulky hole transporting materials (HTMs) with two or four N,N‐di(4‐methoxyphenyl)aminophenyl units have been synthesized. When the EtheneTTPA was used as a hole transporting material in perovskite solar cell, the power conversion efficiency afforded 12.77 % under AM 1.5 G illumination, which is comparable to the widely used spiro‐OMeTAD based solar cell (13.28 %).     

Enhancing the Photocurrent in Diketopyrrolopyrrole-Based Polymer Solar Cells via Energy Level Control

A series of diketopyrrolopyrrole (DPP)-based small band gap polymers has been designed and synthesized by Suzuki or Stille polymerization for use in polymer solar cells. The new polymers contain extended aromatic π-conjugated segments alternating with the DPP units and are designed to increase the free energy for charge generation to overcome current limitations in photocurrent generation of DPP-based polymers. In optimized solar cells with [6,6]phenyl-C(71)-butyric acid methyl ester ([70]PCBM) as acceptor, the new DPP-polymers provide significantly enhanced external and internal quantum efficiencies for conversion of photons into collected electrons. This provides short-circuit current densities in excess of 16 mA cm(-2), higher than obtained so far, with power conversion efficiencies of 5.8% in simulated solar light. We analyze external and internal photon to collected electron quantum efficiencies for the new polymers as a function of the photon energy loss, defined as the offset between optical band gap and open circuit voltage, and compare the results to those of some of the best DPP-based polymers solar cells reported in the literature. We find that for the best solar cells there is an empirical relation between quantum efficiency and photon energy loss that presently limits the power conversion efficiency in these devices.     

宽光谱太阳能电池

太阳能电池的光谱响应特性和光电转换效率与光伏材料的微观能带结构及其宏观组装方式密切相关。无论使用哪种光伏材料,普通单结或单层太阳能电池都只能对部分波段的太阳光进行有效利用。宽光谱研究的目标是要使太阳能电池更好地利用太阳光谱所覆盖的全部波段范围的能量,从而提高太阳能电池光电转换效率。本文从化学角度综述了实现宽光谱太阳能电池的基本方法和当前的研究进展,其中包括叠层太阳能电池、中间带太阳能电池、量子点太阳能电池、热光伏太阳能电池、上转换和下转换、分子基柔性太阳能电池等方法。     

Systematic investigation of benzodithiophene- and diketopyrrolopyrrole-based low-bandgap polymers designed for single junction and tandem polymer solar cells

The tandem solar cell architecture is an effective way to harvest a broader part of the solar spectrum and make better use of the photonic energy than the single junction cell. Here, we present the design, synthesis, and characterization of a series of new low bandgap polymers specifically for tandem polymer solar cells. These polymers have a backbone based on the benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Alkylthienyl and alkylphenyl moieties were incorporated onto the BDT unit to form BDTT and BDTP units, respectively; a furan moiety was incorporated onto the DPP unit in place of thiophene to form the FDPP unit. Low bandgap polymers (bandgap = 1.4-1.5 eV) were prepared using BDTT, BDTP, FDPP, and DPP units via Stille-coupling polymerization. These structural modifications lead to polymers with different optical, electrochemical, and electronic properties. Single junction solar cells were fabricated, and the polymer:PC(71)BM active layer morphology was optimized by adding 1,8-diiodooctane (DIO) as an additive. In the single-layer photovoltaic device, they showed power conversion efficiencies (PCEs) of 3-6%. When the polymers were applied in tandem solar cells, PCEs over 8% were reached, demonstrating their great potential for high efficiency tandem polymer solar cells.     

Density functional theory as a guide for the design of pyran dyes for dye-sensitized solar cells

Abstract  

Using density functional theory and hybrids, we examined several derivatives of the dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran, with the objective of identifying modifications which would improve the properties of dyes for dye-sensitized solar cells. We calculated the electronic structure of numerous derivatives at the HOMO and LUMO energy levels, with the hypothesis that directing the flow of excited electrons to the point of the dye at which the molecule attaches to TiO₂ would increase the energy conversion efficiency of the cell. We also examined the UV–visible absorption spectra of the dyes, with the objective of capturing the maximum amount of solar light. By use of the derivatives we compared the use of two electron-donating groups instead of one, extension of the conjugated chain leading to the attachment point of the dye, use of oxygen versus sulfur or selenium in the dye, and the use of different electron-donating groups. We identified several promising donating groups and determined that the other modifications to the dye are likely to increase solar cell efficiency.     

Influence of fluorination on the microstructure and performance of diketopyrrolopyrrole‐based polymer solar cells

The solar cell performance and microstructure of DPP‐based polymers with different degrees of fluorination are reported. DPP‐based polymers with thiophene–phenyl–thiophene comonomer and thiophene flanking units are studied, with the degree of fluorination of the phenyl unit varied. With bifluorination of the phenyl ring, a higher open circuit voltage is achieved whilst maintaining or even improving the overall solar cell efficiency. While tetrafluorination leads to a further 0.1 V increase in V_OC, reaching a high photo voltage of 0.81 V, overall solar cell performance significantly drops. Microstructural studies using AFM, TEM, Grazing incidence wide‐angle X‐ray scattering (GIWAXS), and Resonant soft X‐ray scattering (R‐SoXS) reveal that bifluorination largely preserves the microstructure of the nonfluorinated system, whereas tetrafluorination results in coarse phase separation between the polymer donor and the fullerene acceptor. Our results demonstrate that the use of an extended comonomer is a promising strategy for optimizing the beneficial effects of fluorination for DPP‐based polymer solar cells, especially in improving the open circuit voltage. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 49–59     

钙钛矿太阳电池的工作机理及性能的主要影响因素

本文综合评述了钙钛矿太阳电池的重要研究成果, 解释了其工作机理并总结了影响电池性能的关键因素: 钙钛矿化学组成、 结晶与形貌、 传输层、 电极和体异质结等. 对钙钛矿太阳电池的未来发展进行了展望.     

Bulk heterojunction polymer solar cells based on binary and ternary blend systems

Polymer solar cells (PSCs) were fabricated using a ternary blend film consisting two conjugated polymers and a soluble fullerene derivative as the donor and acceptor materials, respectively. And, to compare ternary blend system, the single‐component copolymers consisting of the repeating units of each of the copolymers, used in ternary blend solar cells, were designed and synthesized for use as the electron donor materials in binary blend solar cells. We systematically investigated the field‐effect carrier mobilities and the optical, electrochemical, and photovoltaic properties of the copolymers. Under optimized conditions, the binary blend polymer systems showed power conversion efficiencies (PCEs) for the PSCs in the range 3.87–4.16% under AM 1.5 illumination (100 mW cm^?2). All polymers exhibited similar PCEs that did not depend on the ratio of repeating units. The binary blend solar cell containing a single‐component copolymer as the electron donor material performed better than the ternary blend solar cell in this work. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Routes to copper zinc tin sulfide Cu2ZnSnS4 a potential material for solar cells

Power generation through photovoltaics (PV) has been growing at an average rate of 40% per year over the last decade; but has largely been fuelled by conventional Si-based technologies. Such cells involve expensive processing and many alternatives use either toxic, less-abundant and or expensive elements. Kesterite Cu(2)ZnSnS(4) (CZTS) has been identified as a solar energy material composed of both less toxic and more available elements. Power conversion efficiencies of 8.4% (vacuum processing) and 10.1% (non-vacuum processing) from cells constructed using CZTS have been achieved to date. In this article, we review various deposition methods for CZTS thin films and the synthesis of CZTS nanoparticles. Studies of direct relevance to solar cell applications are emphasised and characteristic properties are collated.     

Carbon quantum dots-embedded graphitic carbon nitride nanotubes for enhancing the power conversion efficiency of sensitized solar cells

Graphitic carbon nitride (CN) has been widely used as a photocatalyst. Very few researchers have reported the use of CN in quantum dot-sensitized solar cells (QDSCs). In this study, we prepared nitrogen-rich carbon quantum dot (CQD)-embedded CN nanotubes (CCNTs) with freeze-dried urea and CQD precursors. The prepared CCNTs were used as efficient light harvesters in QDSCs for the first time; their use significantly improved the power conversion efficiency (PCE) of the solar cells compared to those of CQD, CN NT, and bulk CN-sensitized solar cells. The CCNT-sensitized solar cell exhibits 1.01% PCE, which is the highest value among carbon-based QDSCs. Moreover, the CCNTs-sensitized device showed superior photostability over those of CQDs-, CN NTs-, and bulk CN-sensitized devices. The improved performance of the CCNT-sensitized solar cell can be attributed to the facilitated photoelectron transport and suppressed charge recombination. The integration of nitrogen-rich CQDs in CCNTs adjusts the band alignment and maximizes the visible light harvest by reducing the energy barriers, which improves the charge collection efficiency of the device.     

Platinum Alloy Tailored All‐Weather Solar Cells for Energy Harvesting from Sun and Rain

Solar cells that can harvest energy in all weathers are promising in solving the energy crisis and environmental problems. The power outputs are nearly zero under dark conditions for state‐of‐the‐art solar cells. To address this issue, we present herein a class of platinum alloy (PtM_x, M=Ni, Fe, Co, Cu, Mo) tailored all‐weather solar cells that can harvest energy from rain and realize photoelectric conversion under sun illumination. By tuning the stoichiometric Pt/M ratio and M species, the optimized solar cell yields a photoelectric conversion efficiency of 10.38 % under simulated sunlight irradiation (AM 1.5, 100 mW cm^?2) as well as current of 3.90 μA and voltage of 115.52 μV under simulated raindrops. Moreover, the electric signals are highly dependent on the dripping velocity and the concentration of simulated raindrops along with concentrations of cation and anion.     

Can Polymer Solar Cells Open the Path to Sustainable and Efficient Photovoltaic Windows Fabrication?

Sunlight is among the most abundant energy sources available on our planet. Finding adequate solutions to properly and efficiently harvest it is of major importance to potentially solve the global energy crisis. Polymer solar cells have been introduced in the late 20^th century as low‐cost and easily processed alternative to the state‐of‐the‐art silicon photovoltaics. Their power conversion efficiencies, which were initially rather low, are constantly improving and now reach values close to 15 %. As their optical properties can be easily tuned, designing active layer which absorb homogeneously throughout the visible spectrum is relatively simple. These peculiar characteristics enable the possibility to fabricate visibly transparent solar cells with high color rendering indices which can be employed as photovoltaic windows. After reviewing some of the most successful examples of polymer solar cell‐based transparent photovoltaic window fabrication, I will discuss the possibility to produce these devices in a sustainable and/or eco‐friendly manner while maintaining their performances.     

An Isoindigo‐Based “Double‐Cable” Conjugated Polymer for Single‐ Component Polymer Solar Cells

An isoindigo‐based “double‐cable” conjugated polymer bearing perylene bisimide side units was developed via Stille polymerization for application in single‐component polymer solar cells, in which a power conversion efficiency of 1% with broad photo‐response from 300 nm to 800 nm was achieved. There is no evidence of large phase separation confirmed by AFM images and photoluminescence (PL) spectra. The space charge limit current measurements and light intensity dependence measurements indicate that the low electron mobility and the significant recombination of photogenerated charge carriers in active layer mainly account for the low performance of our solar cells. Our results suggest that these “double‐cable” are promising candidates for use in single‐component polymer solar cells with NIR photoresponse.     

Recent Advances in Mechanically Robust and Stretchable Bulk Heterojunction Polymer Solar Cells

Organic bulk heterojunction solar cells are promising candidates as future photovoltaic technologies for large‐scale and low‐cost energy production. It is, therefore, not surprising that research on the design and preparation of these types of organic photovoltaics has attracted a lot of attention since the last two decades, leading to constantly growing values of energy conversion and efficiency. Combined with the possibility of a large‐scale production via roll‐to‐roll printing techniques, bulk heterojunction solar cells enable the fabrication of conformable, light‐weight and flexible light‐harvesting devices for point‐of‐use applications. This perspective review will highlight the recent advances toward mechanically robust and intrinsically stretchable bulk heterojunction solar cells. Mechanically robust fullerene‐based and all‐polymer devices will be presented, as well as a comprehensive overview of the recent challenges and characterization techniques recently developed to overcome some of the challenges of this research area, which is still in its infancy.     

A homopolymer based on double B←N bridged bipyridine as electron acceptor for all-polymer solar cells

A homopolymer based on double B ← N bridged bipyridine was reported as a novel polymer electron acceptor. The resulting all-polymer solar cells show power conversion efficiencies of 2.44%–3.04%.     

A low bandgap polymer based on isoindigo and bis(dialkylthienyl)benzodithiophene for organic photovoltaic applications

A new conjugated polymer PBDTT‐ID based on N‐alkylated isoindigo (ID) and bis(2,3‐dialkylthienyl)‐substituted benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) as repeating units was synthesized. It had an optical bandgap of 1.56 eV and a highest occupied molecular orbital (HOMO) energy level of ?5.71 eV. The optical, electrochemical, and photovoltaic properties of new polymer were compared with previous reported polymer PBDT‐ID , which was based on bis(alkoxy)‐substituted benzo[1,2‐b:4,5‐b′]dithiophene. The new polymer displayed lower HOMO energy level and better absorption properties than polymer PBDT‐ID . The solar cells fabricated with PBDTT‐ID /PC₆₁BM (1:2, w/w) blends as active layers exhibited photoresponse in the range of 300–800 nm. A power conversion efficiency of 4.02% and an open circuit voltage (V_oc) of 0.94 V were achieved in polymer solar cell device based on the new polymer. This was the highest V_oc realized among the isoindigo‐based polymers. The relatively high performances of new polymer in solar cell devices were interpreted in terms of material properties and morphologies of polymer/PCBM blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New benzodithiophene‐ and benzooxadiazole/benzothiadiazole‐based donor–acceptor π‐conjugated polymers for organic photovoltaics

A new set of push‐pull type 2D‐conjugated polymers (P1–P4) were designed and synthesized where A1, A2 (oxygen analogues) and A3, A4 (sulfur analogues) are electron deficient units used as co‐monomers. On introduction of new repeating units into the polymer backbone, significant changes were observed in optoelectronic properties. Furthermore, the heteroatom exchange in new repeating units has also brought notable changes in photophysical properties, in particular P1 and P2 (oxygen analogues) showed bathochromic shift in UV‐vis absorption spectra and deeper HOMO energy levels than P3, P4 (sulfur analogues). Interestingly P1, P3 absorption spectra shows a vibronic shoulder (659, 652 nm) peak in lower energy region, and this might originated from non‐covalent interactions between the electron rich and electron deficient units. In addition, the systematic investigation of these polymers with additive and solvent treatment, yielded in enhanced power conversion efficiency of 4.29% for P3‐based devices in bulk heterojunction organic solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2668–2679     

Toward the Realization of A Practical Diketopyrrolopyrrole‐Based Small Molecule for Improved Efficiency in Ternary BHJ Solar Cells

An easily accessible DPP‐based small molecule ( DMPA‐DTDPP ) has been synthesized by a simple and efficient route. The resulting molecule, when incorporated into a P3HT:PCBM‐based BHJ solar cell, is found to significantly improve the efficiency. The utility of DMPA‐DTDPP as an additive yields an increase in the short circuit current density (J_sc) because DMPA‐DTDPP serves as an energy funnel for P3HT excitons at the P3HT:PCBM interfaces, resulting in an improved overall power conversion efficiency, compared to the P3HT:PCBM control device. Considering the trouble‐free and cost effective synthesis of DMPA‐DTDPP , it may prove very useful in high‐performance solar cells.     

Rigid Nonfullerene Acceptors Based on Triptycene–Perylene Dye for Organic Solar Cells

Three kinds of nonconjugated rigid perylene bisimide (PBI) derivatives based on a triptycene core were designed, synthesized and characterized. The unique three‐dimensional (3D) conformation of triptycene could enable formation of polymer with the favorable morphology for organic polymer solar cells (PSCs) by relieving the self‐aggregation of rigid PBI units. The low‐lying LUMO energy levels of these compounds demonstrated that they are very suitable for use as acceptors in organic solar cells. A higher power conversion efficiency (PCE) of 6.15 % was obtained for the blend film using the compound with two PBI units ( T‐2 ) as the acceptor and commercial poly[[4,8‐bis[5‐(2‐ethylhexyl)thiophene‐2‐yl]benzo[1,2‐b :4,5‐b ′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)‐carbonyl]thieno[3,4‐b ]thiophenediyl]] (PCE‐10) as the electron donor.     

Near-Infrared Nonfullerene Acceptors Based on 4H-Cyclopenta[1,2-b:5,4-b′]dithiophene for Organic Solar Cells and Organic Field-Effect Transistors

The development of nonfullerene small molecular acceptors (NF-SMAs) has dominated the improvement of efficiencies for organic solar cells and the near-infrared (NIR) absorption is the primary feature of NF-SMAs compared with fullerene derivatives. In this article, a series of acceptor-donor-acceptor-structured NF-SMAs (named CPICs ) containing 4H-cyclopenta[1,2-b : 5,4-b′]dithiophene (CPDT) electron donor and F-substituted 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as electron acceptor were designed and synthesized. With the increase of CPDT units, the elongated conjugations broadened the absorption range of the acceptors and tuned their energy levels sequentially. Therefore, their charge-transporting polarities switched from electron-only type to bipolar mode in organic field-effect transistors. Moreover, these changes also influenced the voltages, current densities, and eventual PCEs of their corresponding cells. When blending with PBDB-T, a champion efficiency of 10.01% was achieved in CPIC-2 based cells. This work demonstrated the importance of absorptions, suitable energy levels and charge transports in improving the efficiencies of organic solar cells.