Influence of Average Photon Energy index on solar irradiance characteristics and outdoor performance of photovoltaic modules

Solar spectral irradiance measurements on a routinely basis are relevant to study the influence of solar spectrum on the photovoltaic (PV) module performance, especially for thin film and third generation PV. Two spectroradiometers from EKO were added to the instrumentation available at the ESTER outdoor station of the University of Rome Tor Vergata. A detailed characterisation of the spectral irradiance at the site was carried on during more than 6 months of monitoring activity measuring spectral solar irradiance in the range 350–1700 nm with a time interval of 10 min on a horizontal plane. A wide variety of spectra were acquired in various weather conditions, and indications about the spectra behaviour on a daily and seasonal basis were obtained. Moreover, information about the effect of the weather conditions on the solar radiation spectral distribution were identified. The Average Photon Energy index was used as an indicator of the spectra characteristics. The same index was also used to evidence the solar spectrum influence on polycrystalline and double junction amorphous silicon PV modules. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental solar spectral irradiance until 2500 nm: results and influence on the PV conversion of different materials

In this work, results are presented concerning solar spectral irradiance measurements performed in Madrid in the wavelength range 250–2500 nm, that is, extending the spectral range far away from the wavelengths where PV semiconductors are active. These data were obtained considering a horizontal receiver surface during selected clear days covering the four seasons of the year. PV materials having different spectral responses (m‐Si, a‐Si, CIGS, CdTe) have been considered to calculate spectral factors (SF) taking as reference the standard solar spectrum AM1.5 defined in standard IEC 60904‐3. From these SFs, the influence of natural solar spectral variations in PV conversion has been established. It is shown, for example, that PV technologies based on a‐Si are highly favored, from the spectral point of view, in spring–summer compared to other technologies having broader spectral responses, which are more favored in autumn–winter. From the experimental measured solar spectra, we have calculated Weighed Solar Spectra (WSS) corresponding to the four seasons of the year and also to the whole year. The WSS represents, for a certain period of time, the solar spectrum weighed over the irradiance level. SFs have been calculated for different WSSs showing spectral gains for the four PV materials during almost the full year. Otherwise, it is also shown in this work how the near‐IR part of the solar spectrum affects the evaluation of the solar resource as a whole when reference solar cells made of different PV materials are used. For typical m‐Si, a‐Si, CIGS, and CdTe solar cells, the ratio of I_sc over global irradiance is not constant along a given day showing variations that depend on the season and on the PV material considered. © 2006 John Wiley & Sons, Ltd.     

Change in I–V characteristics of thin‐film photovoltaic (PV) modules induced by light soaking and thermal annealing effects

The performance of photovoltaic (PV) modules is generally rated under standard test conditions (STC). However, the performance of thin‐film photovoltaic modules is not unique even under STC, because of the “metastability”. The effects of the light soaking and thermal annealing shall be incorporated into an appropriate energy rating standard. In this study, the change in I–V characteristics of thin‐film PV modules caused by the metastability was examined by repeated indoor measurements in addition to round‐robin outdoor measurements. The investigated thin‐film modules were copper indium gallium (di)selenide (CIGS), a‐Si : H, and a‐Si : H/µc‐Si : H (tandem) modules. The increase in the performance of the CIGS module between the initial and final indoor measurements was approximately 8%. Because of light‐induced degradation, the indoor performance of the a‐Si : H and a‐Si : H/µc‐Si : H modules decreased by approximately 35% and 20%, respectively. The performance was improved by about 4–6% under high temperature conditions after the initial degradation. The results suggest that the performance of thin‐film silicon modules can seasonally vary by approximately 4–6% only due to thermal annealing and light soaking effects. The effect of solar spectrum enhanced the outdoor performance of the a‐Si : H module by about 10% under low air mass conditions, although that of the a‐Si : H/µc‐Si : H modules showed a little increase. The currents of these a‐Si : H/µc‐Si : H modules may be limited by the bottom cells. Therefore, it is required to optimize the effect of solar spectrum in addition to the effects of light soaking and thermal annealing, in order to achieve the best performance for thin‐film silicon tandem modules. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of solar spectrum and module temperature on outdoor performance of photovoltaic modules in round‐robin measurements in Japan

The performance of six photovoltaic (PV) modules composed of polycrystalline silicon (pc‐Si), amorphous silicon (a‐Si), and hydrogenated amorphous silicon/crystalline silicon (a‐Si:H/c‐Si) modules was investigated at eight locations in Japan from August 2007 to December 2008. In addition, solar irradiance, solar spectrum, and module temperature were simultaneously measured in these round‐robin measurements. In this study, we evaluate quantitatively the effects of module temperature and solar spectrum on the performance of the PV modules as thermal factor (TF) and spectral factor (SF), respectively. Furthermore, we investigate the variation in module performance, which is converted into module performance under standard test conditions (STC) using the TF and SF. In the case of the pc‐Si modules, the variations in performance ratio under STC (PR_STC) for these modules range from 0.056 to 0.074 through the round‐robin measurements. The TF indicates that the contribution of module temperature to the variation in performance is large, between about 15 and 20%. However, the SF suggests that the contribution of solar spectrum is quite small, less than 3%. In the case of the a‐Si modules, the contribution of module temperature is about 8%. The performance is largely influenced by solar spectrum, more than 12% at its maximum. Consequently, the variations in the corrected PR_STC of the a‐Si modules are between 0.117 and 0.141. These large variations may result from the effects of thermal annealing and light soaking. The variation in PR_STC of the a‐Si:H/c‐Si module is similar to that of the pc‐Si modules. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of fullerene solubility on the crystallization of poly(3-hexylthiophene) and performance of photovoltaic devices

The substantial crystallization suppression of poly(3-hexylthiophene) (P3HT) in the untreated P3HT:C60 composite film prepared from o-dichlorobenzene (ODCB) solution has been revealed. Besides, the effective conjugation length of P3HT in this composite has been nearly maintained to that in the solution. The different crystallization behaviors of P3HT in its composites with C60 and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) are mainly attributed to the relative solubility of C60 and PCBM with respect to P3HT in ODCB. The solution to overcome this disadvantage of chain conformation and crystallinity of P3HT in the composite with C60 is thus proposed and finalized by resorting to the addition of low volatile solvent with much higher solubility of C60 than P3HT into the main solvent used, so as P3HT can crystallize before C60 forms crystallites in the solution. The feasibility of this approach has been proven by the improved efficiency of devices based on composites of P3HT and the low cost C60 without resorting to post-treatments. Our results demonstrated in this study could further benefit development of new electron acceptor materials, particularly based on fullerenes and their derivatives, by considering the role of the new materials in determining the crystallization of the other components involved in the composite film.     

Developing a method and simulation model for evaluating the overall energy performance of a ventilated semi‐transparent photovoltaic double‐skin facade

A comprehensive simulation model has been developed in this paper to simulate the overall energy performance of an amorphous silicon (a‐Si) based photovoltaic double‐skin facade (PV‐DSF). The methodology and the model simulation procedure are presented in detail. To simulate the overall energy performance, the airflow network model, daylighting model, and the Sandia Array Performance Model in the EnergyPlus software were adopted to simultaneously simulate the thermal, daylighting, and dynamic power output performances of the PV‐DSF. The interaction effects between thermal, daylighting, and the power output performances of the PV‐DSF were reasonably well modeled by coupling the energy generation, heat‐transfer, and optical models. Simulation results were compared with measured data from an outdoor test facility in Hong Kong in which the PV‐DSF performance was measured. The model validation work showed that most of the simulated results agreed very well with the measured data except for a modest overestimation of heat gains in the afternoons. In particular, the root‐mean‐square error between the simulated monthly AC energy output and the measured quantity was only 2.47%. The validation results indicate that the simulation model developed in this study can accurately simulate the overall energy performance of the semi‐transparent PV‐DSF. This model can, therefore, be an effective tool for carrying out optimum design and sensitivity analyses for PV‐DSFs in different climate zones. The methodology developed in this paper also provides a useful reference and starting point for the modeling of other kinds of semi‐transparent thin‐film PV windows or facades. Copyright © 2015 John Wiley & Sons, Ltd.     

Impact of compositional grading and overall Cu deficiency on the near‐infrared response in Cu(In,Ga)Se2 solar cells

Highly efficient thin film solar cells based on co‐evaporated Cu(In,Ga)Se₂ (CIGS) absorbers are typically grown with a [Ga]/([Ga] + [In]) (GGI) gradient across the thickness and a Cu‐poor composition. Upon increasing the Cu content towards the CIGS stoichiometry, lower defect density is expected, which should lead to increased absorption in the near‐infrared (NIR), diffusion length and carrier collection. Further, optimization of the GGI grading is expected to increase the NIR response. In this contribution [Cu]/([In] + [Ga]) (CGI) values are increased by shortening the deposition stage after the first stoichiometric point. In order to obtain comparable Ga contents at the interface for proper band alignment, the front GGI gradings were actively modified. With a relative CGI increase of 7%, we observe an increased photocurrent, originating from an improved NIR external quantum efficiency response. By characterizing the modified absorber properties by reflection‐transmission spectroscopy, we attribute the observed behavior to changes in the optical properties rather than to improved carrier collection. Cu‐dependent modifications of the NIR‐absorption coefficients are likely to be responsible for the variations in the optical properties, which is supported by device simulations. Adequate re‐adjustments of the co‐evaporation process and of the alkali‐fluorides post‐deposition treatments allow maintaining V_oc and FF values, yielding an overall increase of efficiency as compared to a reference baseline. © 2016 The Authors. Progress in Photovoltaics : Research and Applications published by John Wiley & Sons Ltd.     

掺Cr,Ni对S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论(DFT)的第一性原理方法,在广义梯度近似下计算了Fe中掺Cr或Ni时S原子在Fe(100)面吸附的结构和电子性质,并计算了其分子轨道和吸附能。结果表明:S原子均是吸附在H位最稳定;纯铁时S在Fe(100)面H位的吸附能为-7.70 eV,掺Ni时S原子在H位的吸附能为-7.35 eV,吸附能的相对变化为4.5%;掺Cr时S原子在H位的吸附能为-5.79 eV,吸附能相对纯铁时变化为24.8%,表明掺Cr对S原子在Fe表面的吸附抑制作用更大。对比分析了每种吸附情况下的分波态密度,结果发现掺Cr时具有较高的局域电子云重叠,从而产生的排斥作用抑制了S原子的吸附。     

Influence of the Cu(In,Ga)Se2 thickness and Ga grading on solar cell performance

Thin‐film solar cells with Cu(In,Ga)Se₂ (CIGS) absorber layers ranging from 1.8 to 0.15 μm in thickness were fabricated by co‐evaporation, with both homogeneous and Ga/(Ga + In) graded composition. The absorption of the CIGS layers was determined and compared with corresponding QE measurements in order to obtain the optical related losses. The material characterization included XRD as well as cross‐sectional SEM analysis. Devices with CIGS layers of all thicknesses were fabricated, and down to 0.8–1 μm they showed a maintained high performance (η ∼ 15%). When the CIGS layer was further reduced in thickness the loss in performance increased. The main loss was observed for the short‐circuit current, although the loss was not only due to a reduced absorbance. The open‐circuit voltage was essentially not affected by the reduction of the CIGS thickness, while the fill factor showed a slight decrease. The fill factor loss was eliminated by introducing a Ga/(Ga+In) graded CIGS, which also resulted in an increased open‐circuit voltage of 20–30 mV for all CIGS thicknesses. Device results of 16.1% efficiency at 1.8 μm CIGS thickness, 15.0% at 1.0 μm and 12.1% at 0.6 μm (total area without anti‐reflective coating) were achieved. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of current on the microstructure and performance of (Bi_2Te_3)_(0.2)(Sb_2Te_3)_(0.8) thermoelectric material via field activated and pressure assisted sintering

(Bi_2Te_3)_(0.2)(Sb_2Te_3)_(0.8) thermoelectric material was sintered via a field activated and pressure assisted sintering(FAPAS) process.By applying different current intensity(0,60,320 A/cm~2) in the sintering process,the effects of electric current on the microstructure and thermoelectric performance were investigated.This demonstrated that the application of electric current in the sintering process could significantly improve the uniformity and density of(Bi_2Te_3)_(0.2)(Sb_2Te_3)_(0.8) samples.Whe...     

Structure of chemically deposited Zn(S,O,OH) buffer layer and the effects on the performance of Cu(in,Ga)Se2 solar cell

The effects of the immersion into a NH₃ aqueous solution on the structural characteristics of the chemically deposited Zn(S,O,OH) layer and photovoltaic performance of the CIGS/Zn(S,O,OH) solar cells were investigated with structural and electrical characterizations. The as‐deposited‐Zn(S,O,OH) layer possessed a layered structure of upper Zn(OH)₂ and Zn(S,O) layers, and the upper Zn(OH)₂ layer was removed by the immersion. The conversion efficiency for the CIGS solar cell was improved from 6.8% to 13.7% by removing the upper Zn(OH)₂ layer during the immersion. Copyright © 2015 John Wiley & Sons, Ltd.