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Discovering a competent charge transport layer promoting charge separation in photoelectrodes is a perpetual pursuit in photoelectrochemical (PEC) water splitting to achieve high solar‐to‐hydrogen (STH) conversion efficiency. Here, a conjugated polythiophene framework (CPF‐TTB) on Ta3N5 is elaborately electropolymerized, substantiating the hole transport behavior in their heterojunction. Tailored band structures of the CPF‐TTB/Ta3N5 reinforce the separation of photogenerated carriers, elevating a fill factor of the photoanode modified with a cocatalyst. The enhanced hole extraction enables the NiFeOx/CPF‐TTB/Ta3N5/TiN photoanode to generate a remarkable water oxidation photocurrent density of 9.12 mA cm−2 at 1.23 V versus the reversible hydrogen electrode. A tandem device combining the photoanode with a perovskite/Si solar cell implements an unbiased solar water splitting with a STH conversion efficiency of 6.26% under parallel illumination mode. This study provides novel strategies in interface engineering for metal nitride‐based photoelectrodes, suggesting a promise of the organic–inorganic hybrid photoelectrode for high‐efficiency PEC water splitting. [ABSTRACT FROM AUTHOR]

The fabrication of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin‐film solar cells using the electrochemical deposition (ED), which is valued for its industrial feasibility, offers a cost‐effective and environmentally friendly approach to the carbon‐free and clean energy production. However, the reported power conversion efficiency of approximately 10 % for electrodeposited CZTSSe thin‐film solar cells is lower compared to the alternative methods like sputtering and spin‐coating, which is mainly attributed to the phase inhomogeneity and the rough morphology generated during the ED process. Ensuring the microscopic and macroscopic uniformity of the electrodeposited films is crucial for the improvement of the film quality and the device performances. In this review, strategies to address these challenges including the intrinsic film control such as the deposition mode, pH, concentration of metal ions, and complexing agents, as well as the extrinsic approaches such as doping, substitution of metal elements, and the introduction of interfacial layers. In addition, the prospects for the electrochemically deposited CZTSSe solar cells were presented, focusing on the promising applications in tandem, flexible, and solar water‐splitting devices. Finally, this review will provide technical insights into the ED process for preparing CZTSSe solar cells, outlining a perspective for the future development of highly efficient CZTSSe thin film solar cells. [ABSTRACT FROM AUTHOR]

Over the past couple of decades, immense research has been carried out to understand the photo‐physics of an organic solar cell (OSC) that is important to enhance its efficiency and stability. Since OSCs undergoes complex photophysical phenomenon, studying these factors has led to designing new materials and implementing new strategies to improve efficiency in OSCs. In this regard, the invention of the non‐fullerene acceptorshas greatly revolutionized the understanding of the fundamental processes occurring in OSCs. However, such vital fundamental research from device physics perspectives is carried out on glovebox (GB) processed OSCs and there is a scarcity of research on air‐processed (AP) OSCs. This review will focus on charge carrier dynamics such as exciton diffusion, exciton dissociation, charge‐transfer states, significance of highest occupied molecular orbital‐offsets, and hole‐transfer efficiencies of GB‐OSCs and compare them with the available data from the AP‐OSCs. Finally, key requirements for the fabrication of efficient AP‐OSCs will be presented from a charge‐carrier dynamics perspective. The key aspects from the charge‐carrier dynamics view to fabricate efficient OSCs either from GB or air are provided. [ABSTRACT FROM AUTHOR]

In spite of the high potential economic feasibility of the tandem solar cells consisting of the halide perovskite and the kesterite Cu2ZnSn(S,Se)4 (CZTSSe), they have rarely been demonstrated due to the difficulty in implementing solution‐processed perovskite top cell on the rough surface of the bottom cells. Here, we firstly demonstrate an efficient monolithic two‐terminal perovskite/CZTSSe tandem solar cell by significantly reducing the surface roughness of the electrochemically deposited CZTSSe bottom cell. The surface roughness (Rrms) of the CZTSSe thin film could be reduced from 424 to 86 nm by using the potentiostatic mode rather than using the conventional galvanostatic mode, which can be further reduced to 22 nm after the subsequent ion‐milling process. The perovskite top cell with a bandgap of 1.65 eV could be prepared using a solution process on the flattened CZTSSe bottom cell, resulting in the efficient perovskite/CZTSSe tandem solar cells. After the current matching between two subcells involving the thickness control of the perovskite layer, the best performing tandem device exhibited a high conversion efficiency of 17.5% without the hysteresis effect. [ABSTRACT FROM AUTHOR]

Spiro-OMeTAD is a widely used hole-transporting layer (HTL) material, characterized by high hole mobility and good film-forming properties, in perovskite solar cells (PSCs). However, this material has high synthesis costs, low solubility, dependence on hygroscopic dopants, and a low commercial potential. Recently, we investigated alternative materials with good solubility, simple synthetic methods, and good electrical characteristics for use as hole transport materials (HTM) in triple-cation PSCs. Herein, (E,E,E,E)-4,4′,4″,4′″-[Benzene-1,2,4,5-tetrayltetrakis(ethene-2,1-diyl)]tetrakis[N,N-bis(4-methoxyphenyl)aniline], which has a small molecular weight and similar properties to Spiro-OMeTAD, was assessed for use as a HTM via a pre-test of device performance, including its electrical properties, surface morphology, and coating process method, with PSC efficiencies routinely surpassing 20%. A remarkable open-circuit voltage of 1.111, along with a photovoltaic efficiency of 20.18% was obtained in PSCs using this HTM with dichloromethane (DCM) instead of chlorobenzene, indicative of its potential for the fabrication of resistance components with improved surface uniformity. These results provide insights into DCM as an efficient solvent for small molecule-based HTM. [ABSTRACT FROM AUTHOR]

As a more efficient alternative to the crystalline Si (c‐Si) cell whose performance is approaching its theoretical limit, perovskite (PVSK)/Si tandem solar cells (TSCs) are attracting attention from academia and industry. The tandem device, which can benefit from the maturity of the c‐Si cells and the high performance of the PVSK solar cell, has undergone tremendous development. The expectation for its commercialization is increasing as the device shows conversion efficiencies surpassing those of single‐junction solar cells. In this perspective article, the recent progress of the PVSK/Si TSC is summarized from a viewpoint balanced between academia and industry, by regrouping reported devices depending on the types of Si bottom cells: passivated emitter rear contact, heterojunction with intrinsic thin layer, and polysilicon‐passivated contact. In addition, opto‐electronic characterization methods of the PVSK/Si TSCs are reviewed, which can provide an in‐depth analysis of the subcells that can facilitate the development. [ABSTRACT FROM AUTHOR]

Fluorinated quinoxaline-based small molecules, SM1, SM2, and SM3, were developed as the donor materials for photovoltaic cells. The small molecules containing a 2,3-didodecyl-6,7-difluoroquinoxaline as the electron-deficient unit and thienothiophene as the electron rich units were synthesized by Stille coupling. The small molecules exhibit satisfactory thermal stability and a broad absorption band from 400 to 700 nm. The HOMO/LUMO energy levels of SM1, SM2, and SM3 were –5.70/–3.48, –5.57/–3.42, and –5.66/–3.59 eV, respectively. SM3 with the alkyl group at 4-position in terminal thiophene units has lower HOMO energy levels to increase the VOC value. [ABSTRACT FROM AUTHOR]

Two‐dimensional metal‐organic frameworks (MOFs) are regarded as promising electrocatalysts because of their high surface area and tunable compositions. Herein, a novel nickel‐based 2D MOF for efficient oxygen evolution reaction (OER) has been developed. Ni‐NDC MOF nanosheets (NDC = naphthalene‐2,6‐dicarboxylic acid) are successfully synthesized on a nickel foam (NF) through a surfactant‐assisted one‐step hydrothermal method. The resulting Ni‐NDC@NF possessing a high electrochemically active surface area of 3.06 mF cm−2 exhibits excellent OER performance with a low overpotential of 249 mV at 10 mA cm−2, a small Tafel slope of 74 mV dec−1, 100% faradaic efficiency, and long‐term stability of 24 h at least. For the application of a bifunctional catalyst, NiMo alloy is electrodeposited on the Ni‐NDC@NF to enhance hydrogen evolution reaction activity. The overall water splitting in a two‐electrode configuration of NiMo/Ni‐NDC@NF electrodes as both anode and cathode require only a 1.56 V for 20 mA cm−2. The photovoltaic‐electrocatalysis system powered by the tandem solar cell represents a high solar‐to‐hydrogen efficiency of ≈22%. This work will contribute to inspiring the design of novel MOF composite catalysts using vertically aligned 2D MOF nanosheet architecture, thereby enlarging the potential of MOFs on next‐generation electrocatalysts and energy devices. [ABSTRACT FROM AUTHOR]

Increase in incident light and surface modification of the charge transport layer are powerful routes to achieve high‐performance efficiency of perovskite solar cells (PSCs) by improving the short‐circuit current density (JSC) and charge transport characteristics, respectively. However, few techniques are studied to reduce reflection loss and simultaneously improve the electrical performance of the electron transport layer (ETL). Herein, an inclined fluorine (F) sputtering process to fabricate high‐performance PSCs is proposed. The proposed process simultaneously implements the antireflection effect of F coating and the effect of F doping on a TiO2 ETL, which increases the amount of light transmitted into the PSC due to the extremely low refractive index (≈1.39) and drastically improves the electrical properties of TiO2. Consequently, the JSC of the F coating and doping perovskite solar cell (F‐PSC) increased from 25.05 to 26.01 mA cm−2, and the power conversion efficiency increased from 24.17% to 25.30%. The unencapsulated F‐PSC exhibits enhanced air stability after 900 h of exposure to ambient environment atmosphere (30% relative humidity, 25 °C under dark condition). The inclined F sputtering process in this study can become a universal method for PSCs from the development stage to commercialization in the future. [ABSTRACT FROM AUTHOR]

Power conversion efficiencies (PCEs) of glove‐box (GB) processed, two‐component, single‐junction organic solar cells (OSCs) have recently exceeded 18%. However, their mass‐scale manufacture using roll‐to‐roll (R2R) coating techniques is impracticable if they must be fabricated in an air‐free environment. From a commercialization perspective, efficient air‐processed OSCs are of much greater interest than GB‐processed devices since the vast majority of R2R‐manufacturing infrastructure is designed to operate in the air. Herein, it is reported that controlling the crystallinity of non‐fullerene acceptors plays a key role in determining the properties of blend films. Notably, Y6‐hu (a Y6‐derivative) is shown to exhibits a higher degree of crystallinity when processed in air. Air‐processed OSCs show an outstanding PCE of 17.38%, which, to the best of the authors' knowledge, is the highest PCE yet reported for two‐component‐based OSCs processed in air using halogen‐free solvents. Moreover, opaque large‐area OSC sub‐modules with PCEs of 12.44%, and red‐green‐blue colored semi‐transparent OSC sub‐modules with PCEs of >10% are demonstrated. By understanding how morphological features relate to the charge‐generation dynamics of air‐processed OSCs, a new window is opened for the fabrication of efficient and stable air‐processable organic electronics. [ABSTRACT FROM AUTHOR]

Pb‐free Sn‐based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because of their suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn‐based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO−) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI3) perovskite without using A‐site cationic additives. Moreover, the presence of formate results in a uniform pinhole‐free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate‐treated FASnI3 has improved stability against oxidative Sn degradation. The formate‐treated PSC achieves a power conversion efficiency of 12.11% at a high open‐circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate. [ABSTRACT FROM AUTHOR]

The photoactive layer of non‐fullerene organic solar cells (OSCs) generally consists of a low band‐gap acceptor and conjugated polymer with a deep highest occupied molecular orbital (HOMO) because the hole transfer from the acceptor to the donor as well as the electron transfer from the donor polymer to the acceptor is very important to achieve better performance. Therefore, energy level matching between the HOMO of the donor polymer and the work‐function (WF) of the hole transport layer is required. Since the intrinsic p‐type NiO has a lower WF value, the efficiency of NiO‐based PBDB‐T‐2F:Y6 OSCs is somewhat suppressed. In this work, the energy barrier between the NiO (5.1 eV) and HOMO of PBDB‐T‐2F (5.6 eV) by modifying the NiO surface using a 4‐(trifluoromethyl)benzoic acid (PTF‐BOA) dipole layer (NiO‐PTF‐BOA) is successfully eliminated. The carboxyl group of PTF‐BOA is bonded with Ni atoms on the NiO surface, while the CF3 group attracts electrons, thus resulting in a partial negative charge on the CF3 side. This PTF‐BOA dipole layer induces the vacuum level upshift thus enhancing the work function of NiO‐PTF‐BOA to 5.5 eV. The PBDB‐T‐2F:Y6 OSCs with NiO‐PTF‐BOA exhibit an efficiency of 16.36%, which is the highest reported efficiency for NiO‐based OSCs. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis and photovoltaic properties of IEBICO-4F, IEHICO-4F, IOICO-4F, and IDICO-4F non-fullerene acceptors (NFAs) bearing different types of alkyl chains (2-ehtylhexyl (EH), 2-ethylbutyl (EB), n-octyl (O), and n-decyl (D), respectively). These NFAs are based on the central indacenodithiophene (IDT) donor core and the same terminal group of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-2F), albeit with different side chains appended to the thiophene bridge unit. Although the side chains induced negligible differences between the NFAs in terms of optical band gaps and molecular energy levels, they did lead to changes in their melting points and crystallinity. The NFAs with branched alkyl chains exhibited weaker intermolecular interactions and crystallinity than those with linear alkyl chains. Organic solar cells (OSCs) were fabricated by blending these NFAs with the p-type polymer PTB7-Th. The NFAs with appended branched alkyl chains (IEHICO-4F and IEBICO-4F) possessed superior photovoltaic properties than those with appended linear alkyl chains (IOICO-4F and IDICO-4F). This result can be ascribed mainly to the thin-film morphology. Furthermore, the NFA-based blend films with appended branched alkyl chains exhibited the optimal degree of aggregation and miscibility, whereas the NFA-based blend films with appended linear alkyl chains exhibited higher levels of self-aggregation and lower miscibility between the NFA molecule and the PTB7-Th polymer. We demonstrate that changing the alkyl chain on the π-bridging unit in fused-ring-based NFAs is an effective strategy for improving their photovoltaic performance in bulk heterojunction-type OSCs. [ABSTRACT FROM AUTHOR]

To successfully develop a regioregular polymer, poly[4,8‐bis(5‐(2‐hexyldecyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene][5,5′‐bis(7‐(4‐(2‐butyloctyl)thiophen‐2‐yl)‐6‐fluorobenzo[c][1,2,5]thiadiazol‐4‐yl)‐2,2′‐bithiophene] (PDBD‐FBT), a symmetric monomer synthesized in high yield by tin homo‐coupling reactions. PDBD‐FBT is suitable as a donor material in organic photovoltaics (OPVs) because it shows high crystallinity and strong face‐on packing properties. These properties were amplified by thermal annealing (TA). This causes a power conversion efficiency (PCE) enhancement in PDBD‐FBT‐based OPVs. Using PDBD‐FBT as a polymer donor and 2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐heptylundecyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6‐HU) as an electron acceptor, a PCE of 7.91% was achieved without any additive and TA at optimized active layer film thickness of approximately 100 nm. After TA, a PCE of 12.53% was achieved with a 58% increase compared with the reference devices. Owing to the strong crystallinities, trap‐assisted recombination occurs by excessively formed grain boundaries; however, efficient exciton dissociation sufficiently covers these drawbacks. Even in the approximately 340 nm‐thick film condition, this tendency is more pronounced (73% PCE enhancement is observed from 6.17% to 10.69% of PCE in the without and with TA devices, respectively). Our study demonstrates that it is possible to manufacture thickness‐insensitive OPVs based on regioregular polymers with strong crystallinity and face‐on characteristics, thereby providing a solution to the thickness variation of large‐area organic solar cell modules. [ABSTRACT FROM AUTHOR]

Minimizing optical losses of the incident light at the window layers is one of the effective strategies for high photoresponse to achieve highly efficient perovskite/silicon tandem cells. The enhancement of the photoresponse of monolithic tandem cells via rationally controlling their window layers consisting of C60 and indium tin oxide (ITO) is reported. The optical simulation and experimental results are consistent that employing thinner C60 and ITO layers would reduce the optical losses caused by absorption/reflection of the incident, which should lead to the increased photocurrent density. However, it is found that the enhanced optical properties have to be balanced with the changes in the electrical and structural properties. The thickness of layers is optimized to function as charge collection and protection (during sputtering process) layers. As a result, the optimum design of the window layers maximizes the photoresponse without degrading the device performances, leading to a highly efficient two‐terminal perovskite/silicon tandem solar cell with a power conversion efficiency of 25.63%. [ABSTRACT FROM AUTHOR]

A new accepter unit, 2,3-didodecyl-6,7-difluoroquinoxaline, was prepared and utilized for the synthesis of electron acceptor–donor–acceptor materials for organic solar cells. 2,3-Didodecyl-6,7-difluoroquinoxaline unit was designed to introduce electron-withdrawing F atom in quinoxaline unit to improve deeper HOMO energy levels and higher VOC of the materials. The thienothiophene in conjugated materials has more excellent electron-donating ability to decrease of HOMO energy levels, which improves efficiency by increasing the VOC values. [ABSTRACT FROM AUTHOR]

Herein, planar heterojunctions comprising a nonfullerene small molecular acceptor (NFA) and a polymer donor are demonstrated by transferring polymer films on a water surface on top of NFA layers. So far, most solution‐processed layer‐by‐layer architectures have been reported as sequentially deposited bulk heterojunctions or pseudo‐bilayers because mixed regions at the donor/acceptor interface are inevitable in these methods. By virtue of the unique properties of conjugated polymers such as hydrophobicity and spontaneous film formation on a water surface, the fabrication of NFA/polymer bilayer nanostructures is clearly demonstrated by dramatically simplified methods. These bilayers are successfully rendered into bilayer organic solar cells achieving a power conversion efficiency of up to 7.47%. This reflects that these bilayers have appropriate morphological and optoelectrical properties to be operated as photoactive layers in photovoltaic devices. Further, ultrafast charge transfer from the polymer donor to the NFA and fast carrier mobility are investigated by transient‐absorption spectroscopy and photoinduced charge‐extraction measurements. Fast carrier dynamics are observed, which are essential for the efficient harvest of excitons in photovoltaic devices. It is believed that the formation of planar heterojunctions on water can offer technical diversity for the fabrication methods of the photovoltaic devices. [ABSTRACT FROM AUTHOR]

Semitransparent organic solar cells (STOSCs) have received increasing attention due to promising applications such as building‐integrated photovoltaics. Successful commercialization requires that STOSCs are aesthetically pleasing as well as having balanced power conversion efficiencies (PCEs) and average visible transmittances (AVTs). Non‐fullerene acceptors, which possess excellent electrical/chemical properties, have helped STOSCs to achieve high PCE and AVT; however, research related to modulating color and appearance of STOSCs has lagged behind. Herein, narrow bandgap donor and acceptor (PTB7‐Th and IEICO‐4F) and ultra‐wide bandgap acceptors (T2‐ORH and T2‐OEHRH) are used to achieve semitransparency and controllable device coloration. Blend films with controllable colors including cyan → blue → purple → reddish purple colors are successfully demonstrated, which are controlled by ratios of IEICO‐4F:T2‐ORH or IEICO‐4F:T2‐OEHRH with PTB7‐Th. By incorporating semitransparent electrodes (comprising Sb2O3/Ag/Sb2O3), STOSCs with PCEs of 6–7% are achieved for cyan, aqua, indigo, and purple and ≈4% PCEs for reddish‐purple colors, with AVTs in the range of 23–35%. Moreover, optical properties of blend films are studied via absorption and transmission measurements, whereas the range of colors achieved is quantified using commission internationale de l'éclairage (CIE) chromaticity and CIE L * a * b* color space then represented as RGB color models. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 (CZTSSe) thin‐film solar cells offer various advantages including excellent optical and electrical properties, nontoxic and earth‐abundant raw materials, and a simple fabrication process. However, these devices suffer from a high deficit of the open‐circuit voltage (VOC), mainly caused by interface recombination, which increases with increasing surface roughness. In this study, to achieve a high VOC and enhance the overall device performance, an additional heat treatment process was introduced during the fabrication of co‐electrodeposited rough CZTSSe solar cells, and its effect on the photovoltaic properties was systematically investigated using various characterization techniques including diode analysis, transient photovoltage decay measurement, evaluation of the temperature dependency of the open‐circuit voltage, current–voltage and drive‐level capacitance profile analysis, and electrochemical impedance spectroscopy. At the optimized post‐heat treatment (PHT) temperature of 200°C, a significant increase in the conversion efficiency (as high as 32%, from 7.11% to 9.40%) was observed owing to the change in the interfacial materials properties (i.e., higher conductivity and reduced interfacial nonradiative recombination), which in turn is a consequence of the diffusion of the Cd ions and the expansion of the Cu‐poor/Zn‐rich phase. The PHT‐applied CZTSSe device exhibited a high conversion efficiency close to the record‐high one reported for electrodeposited CZTSSe thin‐film solar cells. These findings confirm the potential of PHT to overcome the serious VOC deficit of CZTSSe device; moreover, this approach could possibly be extended to other device fabrication processes to achieve higher device performance and adopted to commercialization. [ABSTRACT FROM AUTHOR]

The pace of advancement and increasing power conversion efficiencies (PCEs) have provided the possibility for organic solar cells (OSCs) to be commercialized in a variety of applications, including semitransparent photovoltaics. The application of dielectric–metal–dielectric (DMD) transparent electrodes to OSCs is an effective way to achieve semitransparent OSCs with different colors. Herein, a DMD multilayer structure based on two Sb2O3 layers and silver (Ag) thin films as the top electrode is introduced. An ultrathin Sb2O3 layer is deposited between the electron transport layer and the Ag film as a bottom layer for the Sb2O3/Ag/Sb2O3 electrode; this layer inhibits Ag atom diffusion and aggregation, which leads to uniform formation of ultrathin Ag films. The thickness of the middle metal layer influences fill factor and short‐circuit current density values, which correlate well with device resistance and light reflection. For the top Sb2O3 layer, the thickness allows the selective transmittance of specific wavelengths of visible light while reflecting wavelengths that are not transmitted, creating a dichroic effect. OSCs are successfully fabricated using three kinds of colorful active layers in conjunction with Sb2O3/Ag/Sb2O3 electrodes, resulting in vividly colored devices with PCE of 6.33–7.88% and average visible transmittances of 23–30%. [ABSTRACT FROM AUTHOR]

With rapid progress in a power conversion efficiency (PCE) to reach 25%, metal halide perovskite-based solar cells became a game-changer in a photovoltaic performance race. Triggered by the development of the solid-state perovskite solar cell in 2012, intense follow-up research works on structure design, materials chemistry, process engineering, and device physics have contributed to the revolutionary evolution of the solid-state perovskite solar cell to be a strong candidate for a next-generation solar energy harvester. The high efficiency in combination with the low cost of materials and processes are the selling points of this cell over commercial silicon or other organic and inorganic solar cells. The characteristic features of perovskite materials may enable further advancement of the PCE beyond those afforded by the silicon solar cells, toward the Shockley-Queisser limit. This review summarizes the fundamentals behind the optoelectronic properties of perovskite materials, as well as the important approaches to fabricating high-efficiency perovskite solar cells. Furthermore, possible next-generation strategies for enhancing the PCE over the Shockley-Queisser limit are discussed. [ABSTRACT FROM AUTHOR]

We designed and synthesized three novel small molecule donors (SM1, SM2 and SM3) that consist of thiophene as the electron-donating end group and 6,​7-​difluoroquinoxaline moiety as a novel electron-withdrawing core group. The organic low band gap molecules with 6,​7-​difluoroquinoxaline and thiophene units were synthesized using Stille coupling to generate SM1, SM2 and SM3. The absorption of SM2 and SM3 in solution was red shifted due to increased conjugation length of added thiophene units. In case of SM2 and SM3, introduction of hexyl chain in terminal thiophene units improve solubility in organic solvent. The maximum absorption peaks of SM1, SM2 and SM3 in solid thin films were at 482, 505 and 518 nm, respectively. SM3 was red shifted as compare to SM2 due to increased π-π stacking of electron donor materials. [ABSTRACT FROM AUTHOR]

We designed and synthesized two novel low band gap small molecule donors (M1 and M2) that consist of benzo[1,2-b:4,5-b′]dithiophene as the electron-rich core and 6,7-difluoroquinoxaline as the electron-deficient end-group. M1 and M2 with A-D-A type structure were synthesized via Stille coupling reaction for use in OSCs. The absorption maximum of the M1 and M2 in solid thin films exhibited at 536 and 540 nm and absorption onset at 582 and 592 nm, corresponding to band gaps of 2.31 and 2.10 eV, respectively. Although the absorption of the M1 with branched alkyl chain was blue shifted as compared to M2, the branched alkyl chain in benzodithiophene core provide appropriate solubility to provide good OSC performance. [ABSTRACT FROM AUTHOR]

A nonfullerene acceptor (NFA) with acceptor–donor–acceptor (A–D–A) architecture, i‐IEICO‐2F, based on 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene as an electron‐donating core and 2‐(6‐fluoro‐2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)‐propanedinitrile as electron‐withdrawing end groups, is designed and synthesized. i‐IEICO‐2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i‐IEICO‐2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i‐IEICO‐2F exhibit optimized photovoltaic performance including an open‐circuit voltage of 0.93 V, a short‐circuit current density of 16.61 mA cm−2, and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i‐IEICO‐2F‐based devices reach PCEs of >11% without using any additives or post‐treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 °C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X‐ray scattering (GIWAXS) results, i‐IEICO‐2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives. [ABSTRACT FROM AUTHOR]

Tandem device architectures offer a route to greatly increase the maximum possible power conversion efficiencies (PCEs) of polymer solar cells, however, the complexity of tandem cell device fabrication (such as selecting bandgaps of the front and back cells, current matching, thickness, and recombination layer optimization) often result in lower PCEs than are observed in single‐junction devices. In this study, we analyze the influence of front cell and back cell bandgaps and use transfer matrix modeling to rationally design and optimize effective tandem solar cell structures before actual device fabrication. Our approach allows us to estimate tandem device parameters based on known absorption coefficients and open‐circuit voltages of different active layer materials and design devices without wasting valuable time and materials. Using this approach, we have investigated a series of wide bandgap, high voltage photovoltaic polymers as front cells in tandem devices with PTB7‐Th as a back cell. In this way, we have been able to demonstrate tandem devices with PCE of up to 12.8% with minimal consumption of valuable photoactive materials in tandem device optimization. This value represents one of the highest PCE values to date for fullerene‐based tandem solar cells. [ABSTRACT FROM AUTHOR]

Improved performance of polymer-based solar cells based on poly[2,6-(4,4-bis-(2-ethylhexyl)-4H- cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzo-thiadiazole)] PCPDTBT has been obtained by using 1,8-octanedithiol (ODT) as a processing additive in the polymer solution used to spin cast the bulk heterojunction films. Although ultrafast spectroscopy studies indicate that the carrier losses are reduced in the films processed with ODT [similar to the reduced carrier losses after thermal annealing of bulk heterojunction (BHJ) materials made from P3HT:PCBM], the magnitude of the reduction is not sufficient to explain the observed factor of 2 increase in the power conversion efficiency. From the analysis of carrier transport in field effect transistors, we find increased electron mobility in the PCPDTBT:PC70BM composites when fabricated with ODT, which is indicative of enhanced connectivity of PC70BM networks. The improved electron mobility appears to be the primary origin of the improved power conversion efficiency in BHJ films. [ABSTRACT FROM AUTHOR]

ABSTRACT: We report the synthesis of low bandgap polymers with a difluoroquinoxaline unit by Stille polymerization for use in polymer solar cells (PSCs). A new series of copolymers with 2,3‐didodecyl‐6,7‐difluoro quinoxaline as the electron‐deficient unit and alkyloxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophene as the electron‐rich unit were synthesized. The photovoltaic properties of the devices based on the synthesized polymers revealed that the fluorine atoms at the quinoxaline units aid in decreasing the highest occupied molecular orbital (HOMO) energy levels; this in turn increased the open circuit voltage of the devices. The polymers with long alkyl chains exhibited good solubility that increased their molecular weight, but the power conversion efficiency was low. Efficient polymer solar cells were fabricated by blending the synthesized copolymers with PC71BM, and the PCE increased up to 5.11% under 100 mW cm−2 AM 1.5 illumination. These results demonstrate that the importance of having a control polymer to be synthesized and characterized side by side with the fluorine analogues. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1489–1497 [ABSTRACT FROM AUTHOR]

Abstract: Naphthalene diimide (NDI) dimers, NDI–Ph–NDI with a phenyl linker and NDI–Xy–NDI with a xylene linker, are designed and synthesized. The influence of the xylene and phenyl linkers on optical properties, electrochemical properties, morphology, and device performance is systematically investigated. Non‐fullerene organic solar cells (OSCs) with NDI–Ph–NDI show poor device efficiency due to aggregation of polymer chains and/or NDI dimers caused by the highly planar structure of NDI–Ph–NDI. Although NDI–Xy–NDI is a non‐planar structure, uniform surface morphology and weak bimolecular recombination lead to high power conversion efficiencies of 3.11%, which is the highest value in non‐fullerene OSCs with NDI small molecules. [ABSTRACT FROM AUTHOR]

The emerging field of tandem polymer solar cells (TPSCs) enables a feasible approach to deal with the fundamental losses associated with single-junction polymer solar cells (PSCs) and provides the opportunity to propel their overall performance. Additionally, the rational selection of appropriate subcell photoactive polymers with complementary absorption profiles and optimal thicknesses to achieve balanced photocurrent generation are very important issues which must be addressed in order to realize paramount device performance. Here, two side chain fluorinated wide-bandgap π-conjugated polymers P1 (2F) and P2 (4F) in TPSCs have been used. These π-conjugated polymers have high absorption coefficients and deep highest occupied molecular orbitals which lead to high open-circuit voltages ( Voc) of 0.91 and 1.00 V, respectively. Using these π-conjugated polymers, TPSCs have been successfully fabricated by combining P1 or P2 as front cells with PTB7-Th as back cells. The optimized TPSCs deliver outstanding power conversion efficiencies of 11.42 and 10.05%, with high Voc's of 1.64 and 1.72 V, respectively. These results are analyzed by balance of charge mobilities, and optical and electrical modeling is combined to demonstrate simultaneous improvement in all photovoltaic parameters in TPSCs. [ABSTRACT FROM AUTHOR]

A new donor (D)-acceptor (A) conjugate, benzodithiophene-rhodanine-[6,6]-phenyl-C61 butyric acid methyl ester (BDTRh-PCBM) comprising three covalently linked blocks, one of p-type oligothiophene containing BDTRh moieties and two of n-type PCBM, is designed and synthesized. A single component organic solar cell (SCOSC) fabricated from BDTRh-PCBM exhibits the power conversion efficiency (PCE) of 2.44% and maximum external quantum efficiency of 46%, which are the highest among the reported efficiencies so far. The SCOSC device shows efficient charge transfer (CT, ≈300 fs) and smaller CT energy loss, resulting in the higher open-circuit voltage of 0.97 V, compared to the binary blend (BDTRh:PCBM). Because of the integration of the donor and acceptor in a single molecule, BDTRh-PCBM has a specific D-A arrangement with less energetic disorder and reorganization energy than blend systems. In addition, the SCOSC device shows excellent device and morphological stabilities, showing no degradation of PCE at 80 °C for 100 h. The SCOSC approach may suggest a great way to suppress the large phase segregation of donor and acceptor domains with better morphological stability compared to the blend device. [ABSTRACT FROM AUTHOR]

Given that the highest certified conversion efficiency of the organic-inorganic perovskite solar cell (PSC) already exceeds 22 %, which is even higher than that of the polycrystalline silicon solar cell, the significance of new scalable processes that can be utilized for preparing large-area devices and their commercialization is rapidly increasing. From this perspective, the electrodeposition method is one of the most suitable processes for preparing large-area devices because it is an already commercialized process with proven controllability and scalability. Here, a highly uniform NiO x layer prepared by electrochemical deposition is reported as an efficient hole-extraction layer of a p-i-n-type planar PSC with a large active area of >1 cm2. It is demonstrated that the increased surface roughness of the NiO x layer, achieved by controlling the deposition current density, facilitates the hole extraction at the interface between perovskite and NiO x, and thus increases the fill factor and the conversion efficiency. The electrochemically deposited NiO x layer also exhibits extremely uniform thickness and morphology, leading to highly efficient and uniform large-area PSCs. As a result, the p-i-n-type planar PSC with an area of 1.084 cm2 exhibits a stable conversion efficiency of 17.0 % (19.2 % for 0.1 cm2) without showing hysteresis effects. [ABSTRACT FROM AUTHOR]

ABSTRACT Two semicrystalline low band gap polymers based on highly electron-deficient 2,1,3-benzothiadiazole-5,6-dicarboxylicimide (BTI) were synthesized by considering the chain planarity via intrachain noncovalent coulombic interactions. The thiophene-BTI and thienothiophene-BTI based PPDTBTI and PPDTTBTI have a low band gap (∼1.5 eV) via strong intramolecular charge transfer interaction, showing a broad light absorption covering 300∼850 nm. Semicrystalline film morphology was observed for both polymers in the grazing incidence wide angle X-ray scattering measurements. Interestingly, PPDTBTI showed a pronounced edge on packing structure but PPDTTBTI showed predominantly a face on orientation in both pristine and blend films. Different packing patterns influenced significantly the charge carrier transport, recombination and resulting photovoltaic characteristics. The best power conversion efficiency was measured to be 5.47% for PPDTBTI and 6.78% for PPDTTBTI, by blending with the fullerene derivative, PC71BM. Compared to the PPDTBTI blend, PPDTTBTI: PC71BM suffered from the lower open-circuit voltage but showed the substantially higher hole mobility and short-circuit current density with smaller charge recombination, showing very good agreements with molecular structures and morphological characteristics. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3826-3834 [ABSTRACT FROM AUTHOR]

This study demonstrates high-performance, ternary-blend polymer solar cells by modifying a binary blend bulk heterojunction (PPDT2FBT:PC71BM) with the addition of a ternary component, PPDT2CNBT. PPDT2CNBT is designed to have complementary absorption and deeper frontier energy levels compared to PPDT2FBT, while being based on the same polymeric backbone. A power conversion efficiency of 9.46% is achieved via improvements in both short-circuit current density ( JSC) and open-circuit voltage ( VOC). Interestingly, the VOC increases with increasing the PPDT2CNBT content in ternary blends. In-depth studies using ultraviolet photoelectron spectroscopy and transient absorption spectroscopy indicate that the two polymers are not electronically homogeneous and function as discrete light harvesting species. The structural similarity between PPDT2CNBT and PPDT2FBT allows the merits of a ternary system to be fully utilized to enhance both JSC and VOC without detriment to fill-factor via minimized disruption of semi-crystalline morphology of binary PPDT2FBT:PC71BM blend. Further, by careful analysis, charge carrier transport in this ternary blend is clearly verified to follow parallel-like behavior. [ABSTRACT FROM AUTHOR]

ABSTRACT P(BDT-TCNT) and P(DTBDAT-TCNT), which has an extended conjugation length, were designed and synthesized for applications in organic solar cell (OSCs). The solution absorption maxima of P(DTBDAT-TCNT) with the extended conjugation were red-shifted by 5-15 nm compared with those of P(BDT-TCNT). The optical band gaps and highest occupied molecular orbital (HOMO) energy levels of both P(BDT-TCNT) and P(DTBDAT-TCNT) were similar. The structure properties of thin films of these materials were characterized using grazing-incidence wide-angle X-ray scattering and tapping-mode atomic force microscopy, and charge carrier mobilities were characterized using the space-charge limited current method. OSCs were formed using [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor and 3% diphenylether as additive suppress aggregation. OSCs with P(BDT-TCNT) as the electron donor exhibited a power conversion efficiency (PCE) of 4.10% with a short-circuit current density of JSC = 9.06 mA/cm2, an open-circuit voltage of VOC = 0.77 V, and a fill factor of FF = 0.58. OSCs formed using P(DTBDAT-TCNT) as the electron donor layer exhibited a PCE of 5.83% with JSC = 12.2 mA/cm2, VOC = 0.77 V, and FF = 0.62. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3182-3192 [ABSTRACT FROM AUTHOR]

The detailed characterization of a dialkoxyphenylene-difluorobenzothiadiazole based conjugated polymer poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) is reported. PPDT2FBT closely tracks theoretical photocurrent production while maintaining a high fill factor in remarkably thick films. In order to understand the properties that enable PPDT2FBT to function with thick active layers, the effect of film thickness on the material properties and device parameters was carefully studied and compared to three benchmark polymers. Optical modeling, grazing incidence wide angle X-ray scattering, cross-sectional transmission electron microscopy, transient photoconductivity, and extensive device work were carried out and have clarified the key structural features and properties that allow such thick active layers to function efficiently. The unique behavior of thick PPDT2FBT films arises from high vertical carrier mobility, an isotropic morphology with strong, vertical π-π stacking, and a suitable energy band structure. These physical characteristics allow efficient photocurrent extraction, internal quantum efficiencies near 100% and power conversion efficiencies over 9% from exceptionally thick active layers in both conventional and inverted architectures. The ability of PPDT2FBT to function efficiently in thick cells allows devices to fully attenuate incident sunlight while providing a pathway to defect-free film processing over large areas, constituting a major advancement toward commercially viable organic solar cells. [ABSTRACT FROM AUTHOR]

We report the new conjugated polymers using dihydroindeno[2,1- a]indene moiety ( ININE), electron-pushing unit with high planarity, for the organic solar cells ( OSCs). Pull-push mode of conjugated polymers, P1 and P2, containing electron pulling unit of N-alkyl-2,2′-bithiophene-3,3′-dicarboximide ( BTI) and electron-pushing unit of ININE were synthesized for the broader absorption of the solar radiation. By incorporation of electron pulling and pushing units using Stille polymerization with catalyst of Pd(0), the polymers were synthesized. Absorption peaks of the thin films of P2, with thiophene unit linking the electron-pulling and pushing units, was shifted to the region of longer wavelength than P1. Two synthesized polymers provided deep energy levels of highest occupied molecular orbital between −5.76 and −5.59 eV and suitable energy levels of lowest unoccupied molecular orbital between −3.65 and −3.55 eV. [ABSTRACT FROM AUTHOR]

A highly efficient Cu2ZnSn(S,Se)4 (CZTSSe)-based thin-film solar cell (9.9 %) was prepared using an electrochemical deposition method followed by thermal annealing. The Cu-Zn-Sn alloy films was grown on a Mo-coated glass substrate using a one-pot electrochemical deposition process, and the metallic precursor films was annealed under a mixed atmosphere of S and Se to form CZTSSe thin films with bandgap energies ranging from 1.0 to 1.2 eV. The compositional modification of the S/(S+Se) ratio shows a trade-off effect between the photocurrent and photovoltage, resulting in an optimum bandgap of roughly 1.14 eV. In addition, the increased S content near the p-n junction reduces the dark current and interface recombination, resulting in a further enhancement of the open-circuit voltage. As a result of the compositional and interfacial modification, the best CZTSSe-based thin-film solar cell exhibits a conversion efficiency of 9.9 %, which is among the highest efficiencies reported so far for electrochemically deposited CZTSSe-based thin-film solar cells. [ABSTRACT FROM AUTHOR]

Considering that a high compatibility at hybrid organic/inorganic interfaces can be achieved using polar and hydrophilic functionalities, this approach is used to improve inverted polymer solar cell performance by introducing nonionic phosphonate side chains (at 0%, 5%, 15%, and 30% substitution levels) into a series of isoindigo-based polymers (PIIGDT-P n). This approach led to ≈20% improvement in power conversion efficiency compared to a nonmodified control polymer, via an increased short-circuit current ( JSC). This enhancement is believed to stem from reduced nongerminate recombination and improved charge carried extraction when the level of phosphonate substitution is optimized. These results are substantiated by a combination of detailed electrical measurements including space-charged limited current modeling, light intensity-dependent photocurrent ( Jph) analysis, and morphological studies (grazing-incidence wide-angle X-ray scattering and atomic force microscopy). This is the first practical report demonstrating the use of nonionic polar side chains to control charge carrier dynamics in an existing photovoltaic polymer structure. It is envisioned that this simple strategy may be applied to other material systems and yield new materials with the potential for even higher performance. [ABSTRACT FROM AUTHOR]

We report new random copolymers using the electron-deficient unit N-alkyl-2,2′-bithiophene-3,3′-dicarboximide ( BTI) for organic solar cells. For absorption over a broader range of the solar spectrum, push-pull types of conjugated polymers PBTIBDT- 3, PBTIBDT- 5, and PBTIBDT- 7, containing 4,8-bis(2-octyldodecyloxy)benzo[1,2- b;3,4- b']dithiophene ( BDT) as electron-pushing unit and BTI as electron-pulling unit, were synthesized. The polymers were synthesized by coupling electron-pushing and electron-pulling units by Stille polymerization with Pd(0) catalyst. The incorporation of more BTI units induced more red shift of the absorption spectra of the polymer thin films. The device comprising PBTIBDT- 5 and PC71BM (1:1) showed VOC = 0.76 V, JSC = 3.28 mA/cm2, and fill factor ( FF) = 0.51, giving a power conversion efficiency of 1.26%. [ABSTRACT FROM AUTHOR]

Two small molecule donor materials (DTGe(FBTTh2)2 and DTGe(FBTBFu)2) incorporating the dithienogermole (DTGe) moiety with fluorobenzothiadiazole (FBT) and bithiophene (Th2) or benzofuran (BFu) end-capping groups are synthesized and their properties as donor materials in small molecule bulk heterojunction type (BHJ) solar cells are investigated. The DTGe(FBTTh2)2 with Th2 end groups shows outstanding solar cell characteristics with efficiencies up to 6.4% using a standard BHJ architecture and 7.3% using a ZnO optical spacer, while the BFu end-capped DTGe(FBTBFu)2 has slightly wider band gaps and yields slightly higher open circuit voltage ( VOC) at the expense of short circuit current ( JSC) and fill factor (FF). In this study, the DTGe-based molecules are systematically compared to the dithienosilole (DTSi)-based analogues, which are currently among the highest power conversion efficiency (PCE) small molecule solar cell donor materials known. The JSC produced by the DTGe molecule is found to be similar to, or slightly higher than the Si analogue, despite similar absorption characteristics, however, the PCE is similar to the Si analogues due to small decreases in VOC and FF. This report marks the first small molecule BHJ based on a Ge-containing heterocycle with PCE over 7%. [ABSTRACT FROM AUTHOR]

A ternary blend polymer solar cell (PSC) comprising a semicrystalline polymer and two fullerene derivatives (C60, C70) shows a substantial increase in energy conversion efficiency as compared to that of corresponding binary blend PSCs. The enhancement in device efficiency results from an increase in short‐circuit current density and a minimization of the fill factor decrease at the optimum blend ratio. [ABSTRACT FROM AUTHOR]

Organic optoelectronic devices including organic light-emitting diodes (OLEDs) and polymer solar cells (PSCs) have many advantages, including low-cost, mechanical flexibility, and amenability to large-area fabrication based on printing techniques, and have therefore attracted attention as next-generation flexible optoelectronic devices. Although almost 100% internal quantum efficiency of OLEDs has been achieved by using phosphorescent emitters and optimizing device structures, the external quantum efficiency (EQE) of OLEDs is still limited due to poor light extraction. Also, although intensive efforts to develop new conjugated polymers and device architectures have improved power conversion efficiency (PCE) up to 8%-9%, device efficiency must be improved to >10% for commercialization of PSCs. The surface plasmon resonance (SPR) effect of metal nanoparticles (NPs) can be an effective way to improve the extraction of light produced by decay of excitons in the emission layer and by absorption of incident light energy within the active layer. Silver (Ag) NPs are promising plasmonic materials due to a strong SPR peak and light-scattering effect. In this review, different SPR properties of Ag NPs are introduced as a function of size, shape, and surrounding matrix, and review recent progress on application of the SPR effect of AgNPs to OLEDs and PSCs. [ABSTRACT FROM AUTHOR]

Multijunction (MJ) solar cells have the potential to operate across the entire solar spectrum, for ultrahigh efficiencies in light to electricity conversion. Here an MJ cell architecture is presented that offers enhanced capabilities in photon recycling and photon extraction, compared to those of conventional devices. Ideally, each layer of a MJ cell should recycle and re-emit its own luminescence to achieve the maximum possible voltage. This design involves materials with low refractive indices as interfaces between sub-cells in the MJ structure. Experiments demonstrate that thin-film GaAs devices printed on low-index substrates exhibit improved photon recycling, leading to increased open-circuit voltages ( Voc), consistent with theoretical predictions. Additional systematic studies reveal important considerations in the thermal behavior of these structures under highly concentrated illumination. Particularly when combined with other optical elements such as anti-reflective coatings, these architectures represent important aspects of design for solar cells that approach thermodynamic efficiency limits for full spectrum operation. [ABSTRACT FROM AUTHOR]

Highly efficient copper-zinc-tin-selenide (Cu2ZnSnSe4; CZTSe) thin-film solar cells are prepared via the electrodepostion technique. A metallic alloy precursor (CZT) film with a Cu-poor, Zn-rich composition is directly deposited from a single aqueous bath under a constant current, and the precursor film is converted to CZTSe by annealing under a Se atmosphere at temperatures ranging from 400 °C to 600 °C. The crystallization of CZTSe starts at 400 °C and is completed at 500 °C, while crystal growth continues at higher temperatures. Owing to compromises between enhanced crystallinity and poor physical properties, CZTSe thin films annealed at 550 °C exhibit the best and most-stable device performances, reaching up to 8.0 % active efficiency; among the highest efficiencies for CZTSe thin-film solar cells prepared by electrodeposition. Further analysis of the electronic properties and a comparison with another state-of-the-art device prepared from a hydrazine-based solution, suggests that the conversion efficiency can be further improved by optimizing parameters such as film thickness, antireflection coating, MoSe2 formation, and p-n junction properties. [ABSTRACT FROM AUTHOR]

ABSTRACT Low bandgap polymers with dithienylquinoxaline moieties based on 6H-phenanthro[1,10,9,8- cdefg]carbazole were synthesized via the Suzuki coupling reaction. Alkoxy groups were substituted at two different positions on the phenyl groups of the quinoxaline units of these polymers: in the para-position (PPQP) and in the meta-position (PPQM). The two polymers showed similar physical properties: broad absorption in the range of 400-700 nm, optical bandgaps of ∼1.8 eV, and the appropriate frontier orbital energy levels for efficient charge transfer/separation at polymer/PC71BM interfaces. However, the PPQM solar cell achieved a higher PCE due to its higher Jsc. Our investigation of the morphologies of the polymer:PC71BM blend films and theoretical calculations of the molecular conformations of the polymer chains showed that the polymer with the meta-positioned alkoxy group has better miscibility with PC71BM than the polymer with the para-positioned alkoxy group because the dihedral angle of its phenyl group with respect to the quinoxaline unit is higher. This higher miscibility resulted in a polymer:PC71BM blend film with a better morphology and thus in a higher PCE. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 796-803 [ABSTRACT FROM AUTHOR]

Among ternary oxides, Zn2SnO4 (ZSO) is considered for dye-sensitized solar cells (DSSCs) because of its wide bandgap, high optical transmittance, and high electrical conductivity. However, ZSO-based DSSCs have a poor performance record owing largely to the absence of systematic efforts to enhance their performance. Herein, general strategies are proposed to improve the performance of ZSO-based DSSCs involving interfacial engineering/modification of the photoanode. A conformal ZSO thin film (blocking layer) deposited at the fluorine-doped tin oxide-electrolyte interface by pulsed laser deposition suppressed the back-electron transfer effectively while maintaining a high optical transmittance, which resulted in a 22 % improvement in the short-circuit photocurrent density. Surface modification of ZSO nanoparticles (NPs) resulted in an ultrathin ZnO shell layer, a 9 % improvement in the open-circuit voltage, and a 4 % improvement in the fill factor because of the reduced electron recombination at the ZSO NPs-electrolyte interface. The ZSO-based DSSCs exhibited a faster charge injection and electron transport than their TiO2-based counterparts, and their superior properties were not inhibited by the ZnO shell layer, which indicates their feasibility for highly efficient DSSCs. Each interfacial engineering strategy could be applied to the ZSO-based DSSC independently to lead to an improved conversion efficiency of 6 %, a very high conversion efficiency for a non-TiO2 based DSSC. [ABSTRACT FROM AUTHOR]

A semicrystalline low-bandgap polymer (PDTPBT) based on alternating dithienopyrrole and benzothiadiazole moieties as a pair of the indene-C60 bisadduct (ICBA) for polymeric solar cells is reported. The lowest unoccupied molecular orbital (LUMO) level of PDTPBT is measured to be −3.47 eV, ensuring sufficient energy offset for photoinduced charge transfer to ICBA. Photovoltaic cells are fabricated with ICBA and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor. By replacing PC71BM with ICBA, the open-circuit voltage is increased by 0.23 V and the resulting power conversion efficiency is improved from 1.17% to 1.71%. To optimize the ICBA-based devices, crystalline low-bandgap structures should be designed carefully as a pair of ICBA by considering the energy-level offset for charge separation and crystalline interchain ordering, for minimizing the intercalated ICBAs inside the polymer domain. [ABSTRACT FROM AUTHOR]