A self‐calibrating led‐based solar test platform

A compact platform for testing solar cells is presented. The light source comprises a multi‐wavelength high‐power LED (light emitting diode) array allowing the homogenous illumination of small laboratory solar cell devices (substrate size 50 × 25 mm) within the 390–940 nm wavelength range. The spectrum can be synthesized by independent tuning of the 18 different wavelengths to mimic AM1.5G as well as various indoor lamp spectra. The intensity can be controlled with a 2¹⁴‐bit accuracy and intensities up to 3 suns are possible with an approximate AM1.5G spectral distribution. For several wavelengths intensities up to 10 suns is possible, and for a few wavelengths up to 30 suns can be reached. The setup is equipped with reference diodes and an optical fibre coupling enabling calibration, monitoring and control of the light impinging on the sample. Through a computer controlled interface, it is possible to perform all the commonly employed measurements on the solar cell at very high speed without moving the sample. In particular, the LED‐based illumination system provides an alternative to light‐biased incident photon‐to‐current efficiency measurement to be performed which we demonstrate. Both top and bottom contact is possible and the atmosphere can be controlled around the sample during measurements. The setup was developed for the field of polymer and organic solar cells with particular emphasis on enabling different laboratories to perform measurements in the same manner and obtain a common basis for comparing data. The use of the platform is demonstrated using a standard P3HT:PCBM polymer solar cell but is generally applicable to any solar cell technology with a spectral response in the 390–950 nm region. Copyright © 2010 John Wiley & Sons, Ltd.     

太阳模拟器的新发展

太阳模拟器作为一种重要的试验与测试设备正广泛应用于航天领域和太阳能利用领域。介绍了使用最多的传统型太阳模拟器的结构组成和工作原理,论述了其优缺点及存在价值。着重叙述了当今涌现的具有代表性的新型太阳模拟器的系统组成和实现形式,如LED太阳模拟器、多光源太阳模拟器、均光棒太阳模拟器、积分球太阳模拟器、光纤传输太阳模拟器和运动式太阳模拟器等。并对它们进行了比较分析,总结了其发展趋势。     

Transparent conductive oxide‐less three‐dimensional cylindrical dye‐sensitized solar cell fabricated with flexible metal mesh electrode

A cylindrical transparent conductive oxide‐less dye‐sensitized solar cell (DSSC) consisting of glass tube/stainless steel mesh–TiO₂–dye/gel electrolytes/Pt‐Ti rod having capability of self‐light trapping is reported. Replacing the glass tube with heat‐shrinkable tube to reduce electrolyte gap and optical loss due to light transmission and reflection led to the enhancement in the power conversion efficiency from 2.61% to 3.91%. Profiling of the current distribution measured by laser beam‐induced current exhibited nearly the same current in the axial and radial directions, suggesting that light reflection on a cylindrical DSSC does not affect the efficiency seriously. Optimized best DSSC in this novel device architecture gave a short‐circuit current density of 11.94 mA/cm², an open‐circuit voltage of 0.71 V and a fill factor of 0.66 leading to the power conversion efficiency of 5.58% at AM 1.5 under simulated solar irradiation. Copyright © 2011 John Wiley & Sons, Ltd.     

Measuring the External Quantum Efficiency of Two‐Terminal Polymer Tandem Solar Cells

Tandem configurations, in which two cells are stacked and connected in series, offer a viable approach to further increase the power conversion efficiency (PCE) of organic solar cells. To enable the future rational design of new materials it is important to accurately assess the contributions of individual subcells. Such accurate measurement of the external quantum efficiency (EQE) of the subcells of two‐terminal organic or polymer tandem solar cells poses specific challenges, caused by two characteristics of these cells, i.e. a sub‐linear light intensity dependence of the current and a field‐assisted charge collection. These properties necessitate that EQE experiments are carried out under representative illumination conditions and electrical bias to maintain short‐circuit conditions for the addressed subcell. We describe a method to determine the magnitudes of the bias illumination and bias voltage during EQE measurements, based on the behavior of single junction cells and optical modeling. The short‐circuit current densities of the subcells obtained by convolution of the EQE with the AM1.5G solar spectrum are consistent with those obtained from optical modeling and correctly predict the current density–voltage characteristics of the tandem cell under AM1.5G conditions.     

Short‐circuit current of solar cells under artificial light

A model to estimate the short‐circuit current of a solar cell under artificial light from the short‐circuit current of the same solar cell under AM1.5 1 kW/m² is described. The results may help designers of solar‐powered portable equipment and consumer products working indoors or under a mixture of artificial and sunlight. It is concluded that the ratio of the short‐circuit currents of the same solar cell generated under fluorescent light of 1 lux illuminance divided by the short‐circuit current generated under standard 1 Sun AM1.5 conditions is around 3 × 10⁻⁶ for typical crystalline silicon and CIS solar cells. This value is one order of magnitude greater if the light source considered is an incandescent lamp. In the case of amorphous silicon solar cells the value of the ratio is close to 8 × 10⁻⁶ either for fluorescent or incandescent lamps. CdTe solar cells are also considered, and this factor is about 4 × 10⁻⁶ under fluorescent light, and four times bigger when an incandescent lamp is used. Some measurements performed validate the figures obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Optimum Design of Dye‐Sensitized Solar Module for Building‐Integrated Photovoltaic Systems

This paper presents a method for determining the optimum active‐area width (OAW) of solar cells in a module architecture. The current density–voltage curve of a reference cell with a narrow active‐area width is used to reproduce the current density profile in the test cell whose active area width is to be optimized. We obtained self‐consistent current density and electric potential profiles from iterative calculations of both properties, considering the distributed resistance of the contact layers. Further, we determined the OAW that yields the maximum efficiency by calculating efficiency as a function of the active‐area width. The proposed method can be applied to the design of the active area of a dye‐sensitized solar cell in Z‐type series connection modules for indoor and building‐integrated photovoltaic systems. Our calculations predicted that OAW increases as the sheet resistances of the contact layers and the intensity of light decrease.     

Characteristics of large‐scale nanohole arrays for thin‐silicon photovoltaics

Nanostructured crystalline silicon is promising for thin‐silicon photovoltaic devices because of reduced material usage and wafer quality constraint. This paper presents the optical and photovoltaic characteristics of silicon nanohole (SiNH) arrays fabricated using polystyrene nanosphere lithography and reactive‐ion etching (RIE) techniques for large‐area processes. A post‐RIE damage removal etching is subsequently introduced to mitigate the surface recombination issues and also suppress the surface reflection due to modifications in the nanohole sidewall profile, resulting in a 19% increase in the power conversion efficiency. We show that the damage removal etching treatment can effectively recover the carrier lifetime and dark current–voltage characteristics of SiNH solar cells to resemble the planar counterpart without RIE damages. Furthermore, the reflectance spectra exhibit broadband and omnidirectional anti‐reflective properties, where an AM1.5 G spectrum‐weighted reflectance achieves 4.7% for SiNH arrays. Finally, a three‐dimensional optical modeling has also been established to investigate the dimension and wafer thickness dependence of light absorption. We conclude that the SiNH arrays reveal great potential for efficient light harvesting in thin‐silicon photovoltaics with a 95% material reduction compared to a typical cell thickness of 200 µm. Copyright © 2012 John Wiley & Sons, Ltd.     

Thin‐film (25.5 μm) solar cells from layer transfer using porous silicon with 32.7 mA/cm2 short‐circuit current density

We fabricate a 25.5‐μm‐thick monocrystalline Si solar cell with a confirmed power conversion efficiency of 15.4% and an area of 3.88 cm² using a layer transfer process with porous Si. The process is free of photolithography and contains no high‐temperature oxidation steps. We investigate three design features that improve the short‐circuit current density to a value of 32.7 mA/cm² under AM1.5 illumination. The detached back reflector contributes 2 mA/cm², a reduced front‐surface reflectance accounts for an additional 2 mA/cm² and a reduced base doping increases the current density by 1 mA/cm². Copyright © 2002 John Wiley & Sons, Ltd.     

Enhanced Photocurrent Spectral Response in Low‐Bandgap Polyfluorene and C70‐Derivative‐Based Solar Cells

Plastic solar cells have been fabricated using a low‐bandgap alternating copolymer of fluorene and a donor–acceptor–donor moiety (APFO‐Green1), blended with 3′‐(3,5‐bis‐trifluoromethylphenyl)‐1′‐(4‐nitrophenyl)pyrazolino[70]fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, λ < 500 nm and 600 < λ < 1000 nm. The BTPF70 absorbs light at λ < 700 nm. A broad photocurrent spectral response in the wavelength range 300 < λ < 1000 nm is obtained in solar cells. A photocurrent density of 3.4 mA cm^–2, open‐circuit voltage of 0.58 V, and power‐conversion efficiency of 0.7 % are achieved under illumination of AM1.5 (1000 W m^–2) from a solar simulator. Synthesis of BTPF70 is presented. Photoluminescence quenching and electrochemical studies are used to discuss photoinduced charge transfer.     

Stepwise measurement procedure for the characterization of large‐area photovoltaic modules

In this paper, we present an indoor measurement procedure for characterizing the electrical performance of large aperture photovoltaic modules. Because of the fact that sun simulators, especially for concentrator photovoltaic applications, are strongly limited in the size of the uniformly illuminated area, we developed a measurement procedure that allows characterizing modules with a larger aperture area than the aperture provided by the sun simulator. The procedure is based on the concept of stepwise illumination of the module area and measurement of the corresponding I–V curves—without the need to contact the subunits directly. Using the additionally measured dark I–V curve of the module, the characteristic I–V curve of the full module can be calculated. Copyright © 2015 John Wiley & Sons, Ltd.     

A Thiophene‐Based Anchoring Ligand and Its Heteroleptic Ru(II)‐Complex for Efficient Thin‐Film Dye‐Sensitized Solar Cells

A novel heteroleptic Ru^II complex (BTC‐2) employing 5,5′‐(2,2′‐bipyridine‐4,4′‐diyl)‐bis(thiophene‐2‐carboxylic acid) (BTC) as the anchoring group and 4,4′‐ dinonyl‐2,2′‐bipiridyl and two thiocyanates as ligands is prepared. The photovoltaic performance and device stability achieved with this sensitizer are compared to those of the Z‐907 dye, which lacks the thiophene moieties. For thin mesoporous TiO₂ films, the devices with BTC‐2 achieve higher power conversion efficiencies than those of Z‐907 but with a double‐layer thicker film the device performance is similar. Using a volatile electrolyte and a double layer 7 + 5 μm mesoporous TiO₂ film, BTC‐2 achieves a solar‐to‐electricity conversion efficiency of 9.1% under standard global AM 1.5 sunlight. Using this sensitizer in combination with a low volatile electrolyte, a photovoltaic efficiency of 8.3% is obtained under standard global AM 1.5 sunlight. These devices show excellent stability when subjected to light soaking at 60 °C for 1000 h. Electrochemical impedance spectroscopy and transient photovoltage decay measurements are performed to help understand the changes in the photovoltaic parameters during the aging process. In solid state dye‐sensitized solar cells (DSSCs) using an organic hole‐transporting material (spiro‐MeOTAD, 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene), the BTC‐2 sensitizer exhibits an overall power conversion efficiency of 3.6% under AM 1.5 solar (100 mW cm^?2) irradiation.     

Charge Generation and Photovoltaic Operation of Solid‐State Dye‐Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene‐Based Sensitizer

An investigation of the function of an indolene‐based organic dye, termed D149, incorporated in to solid‐state dye‐sensitized solar cells using 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxypheny‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon‐to‐current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10 mW cm^?2. However, a considerable nonlinearity in the photocurrent as intensities approach “full sun” conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100 mW cm^?2. The influence of dye‐loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time‐correlated single‐photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO₂ is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro‐OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons “trapped” within the dye phase, equivalent to 1.8 × 10¹⁷ cm^?3 under full sun illumination. it is believed that this localized space charge build‐up upon the sensitizer is responsible for the non‐linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions.     

Perovskite Photovoltaics for Dim‐Light Applications

The use of photovoltaic cells with an organometallic perovskite as the active layer for indoor dim‐light energy harvesting is evaluated. By designing the electron‐transporting materials and fabrication processes, the traps in the perovskite active layers and carrier dynamics can be controlled, and efficient devices are demonstrated. The best‐performing small‐area perovskite photovoltaics exhibit a promising high power conversion efficiency up to ≈27.4%, no hysteresis behavior, and an exceptionally low maximum power point voltage variation of ≈0.1 V under fluorescent lamp illumination at 100–1000 lux. The 5.44 cm² large‐area device also shows a high efficiency of 20.4% and a promising long‐term stability. Compared with the most efficient inorganic and organic solar cells nowadays, the competitive efficiency, low fabrication cost, and low raw material costs make perovskite photovoltaics ideal for indoor light harvesting and as Internet of Things power provider.     

卫星仿真测试用太阳模拟器和地球模拟器设计

讨论了卫星姿态仿真用太阳模拟器的设计要求,详细叙述了太阳模拟器光学系统的结构及主要设计部分的设计内容、方法、过程和关键技术.针对高轨道和低轨道两种情况,介绍了地球模拟器的研制方案.     

Polymer Solar Cells Based on a Low‐Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850 nm

Polymer solar cells have been fabricated from a recently synthesized low band‐gap alternating polyfluorene copolymer, APFO‐Green2, combined with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850 nm and a peak of > 10 % located at 650 nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0 mA cm^–2, photovoltage of 0.78 V, and power conversion efficiency of 0.9 % have been achieved in solar cells based on this new low‐bandgap polymer under the illumination of air mass 1.5 (AM 1.5) (1000 W m^–2) from a solar simulator.     

Fabrication of highly transparent self‐cleaning protection films for photovoltaic systems

A moth‐eye anti‐reflective structure was fabricated by hot‐embossing and UV nanoimprint lithography on a solar cell protective film to suppress the reflection of incident light. Moreover, a superhydrophobic surface was developed by reducing the surface energy by forming a hydrophobic self‐assembled monolayer coating on an anti‐reflective structured resin surface. Therefore, the transmittance of incident light was increased by the anti‐reflective structure. As a result, the solar cell efficiency was enhanced and the total accumulated electrical energy generated by a solar cell with a nano‐patterned polymeric film was increased. The efficiency of each solar cell was evaluated by an analysis of its I‐V characteristics using a solar simulator, and the external quantum efficiency according to the wavelength of incident light was analyzed by using an incident photon‐to‐current conversion efficiency system. Finally, the enhancement of the generated power was confirmed by a field test and a power charging experiment. Copyright © 2012 John Wiley & Sons, Ltd.     

Four‐junction solar cells using lattice‐matched II–VI and III–V semiconductors

Four‐junction solar cells are designed using lattice‐matched II–VI (ZnCdSeTe) and III–V (AlGaAsSb) semiconductors grown on GaSb substrates. These materials have a zinc blende crystal structure, similar thermal expansion coefficients, and bandgaps that cover the entire solar spectrum. Numerical simulations of the energy conversion efficiencies of various designs for both the AM0 and AM1.5D spectra are performed using published material parameters. These results indicate that the achievable 1 sun AM0 efficiency is 43% for an optimal design and 40% for a more practical design; for comparison the ideal limit provided by Henry's model is 49%. While for the AM1.5D spectrum an optimal design can reach 46% under 1 sun and 55% under 1000 suns while a more practical design can reach 44 and 54%, respectively; for comparison Henry's model gives 51 and 62%, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

大光斑高均匀度发散式太阳模拟器设计

为了实现大光斑直径高均匀度太阳辐照模拟,设计了大光斑发散式太阳模拟器。根据太阳光谱分布特性选取短弧氙灯作为光源,建立光源功率计算模型;基于成像倍率和氙弧峰值点离焦量之间的关系,优化设计聚光系统和光学积分器,提高太阳模拟器的辐照均匀度;同时,结合短弧氙灯的光谱特性,建立光谱匹配模型,设计光学滤光片在不同波长的透过率。实验结果表明:设计的发散式太阳模拟器辐照面积为2 m,当工作距离为6、8、10 m时,辐照不均匀度分别优于3.33%、3.51%和4.3%,且光谱与AM1.5太阳光谱A级标准相匹配。     

Temperature dynamics of multijunction concentrator solar cells up to ultra‐high irradiance

We report experimental results for the effect of irradiance (from 12 up to 8600 suns) on the temperature coefficients of the key performance parameters of multijunction concentrator solar cells, with a flash‐like, real‐sun optical system. Particular attention is paid to the time scales and magnitudes of junction heating, hence the degree to which the cell can be deemed isothermal. The implications for corresponding measurements from solar simulators with pulsed artificial light and for the performance evaluation of concentrator photovoltaics are also addressed. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of spectrum on the power rating of amorphous silicon photovoltaic devices

The effects of different spectra on the laboratory based performance evaluation of amorphous silicon solar cells is investigated using an opto‐electrical model which was developed specifically for this purpose. The aim is to quantify uncertainties in the calibration process. Two main uncertainties arise from the differences in the test spectrum and the standard spectrum. First, the mismatch between reference cells and the measured device, which is shown to be voltage dependent in the case of amorphous silicon devices. Second, the fill factor of the device is affected by different spectra. Different cell structures and states (specifically different i‐layer thickness and levels of degradation) for the different light sources are investigated in this work. These sources are different solar simulators, LED sources, Tungsten as well as the standard terrestrial AM1.5G radiation. It is shown that the performance cannot be evaluated by short circuit current alone. The voltage dependent quantum efficiency of p‐i‐n devices can introduce a mismatch in the P_MPP of 1% for 250 nm i‐layer devices in as prepared state, rising to up to 4% for the 600 nm i‐layer devices at degraded state. Copyright © 2011 John Wiley & Sons, Ltd.