多晶薄膜CdS／CdTe太阳电池

报道了转换效率为１４．６％～１５．８％的多晶薄膜ＣｄＳ／ＣｄＴｅ太阳电池的研制。用ＭＯＣＶＤ法，在玻璃衬底上制备ＳｎＯ＿２和ＳｎＯ＿２：Ｆ薄膜，水溶液化学淀积法获得８０～１００ｎｍ厚的ＣｄＳ薄膜和密堆积升华法制备５μｍ厚ＣｄＴｅ薄膜，ＣｄＳ／ＣｄＴｅ太阳电池的短路电流密度高达２４～２５ｍＡ／ｃｍ￣２。同时，对各层薄膜晶形和微观结构进行了分析研究。     

CdS/CdTe叠层太阳电池的制备及其性能

CdS/CdTe太阳电池是薄膜太阳电池研究工作的一个重要方向.为了提高开路电压Voc、改善电池的光谱响应,进而提高电池的转换效率,在此提出CdS/CdTe叠层太阳电池结构.文中,叠层电池的顶电池由CdS/CdTe超薄层构成;底电池由CdS/CdTe薄膜层构成.经分析测试,实验制备的CdS/CdTe叠层太阳电池具有明显的叠层结构,开路电压最高达到了852mV,短路电流密度最大为13mA/cm2,填充因子最高为55.2%,这种叠层电池的效率达到了8.16%(0.071cm2).研究表明相对于传统的单层CdS/CdTe太阳电池,CdS/CdTe叠层电池的制备对研究如何提高CdS/CdTe太阳电池的光伏性能有一定的参考价值.     

CdS/CdTe叠层太阳电池的制备及其性能

CdS/CdTe太阳电池是薄膜太阳电池研究工作的一个重要方向.为了提高开路电压Voc、改善电池的光谱响应,进而提高电池的转换效率,在此提出CdS/CdTe叠层太阳电池结构.文中,叠层电池的顶电池由CdS/CdTe超薄层构成;底电池由CdS/CdTe薄膜层构成.经分析测试,实验制备的CdS/CdTe叠层太阳电池具有明显的叠层结构,开路电压最高达到了852mV,短路电流密度最大为13mA/cm2,填充因子最高为55.2%,这种叠层电池的效率达到了8.16%(0.071cm2).研究表明相对于传统的单层CdS/CdTe太阳电池,CdS/CdTe叠层电池的制备对研究如何提高CdS/CdTe太阳电池的光伏性能有一定的参考价值.     

CdS/CdTe太阳电池的背接触

磷硝酸腐蚀是一种适宜于工业化生产的背表面刻蚀工艺.文中采用磷硝酸腐蚀CdTe薄膜,并用溴甲醇腐蚀作为对照实验,研究了两种腐蚀对材料性质的影响.随后用真空蒸发法分别沉积了四种背接触层,提出了适宜于工业化生产的背接触技术,并从实验和理论上对两种背接触结构的CdTe太阳电池进行了分析.     

CdS/CdTe太阳电池的背接触

磷硝酸腐蚀是一种适宜于工业化生产的背表面刻蚀工艺.文中采用磷硝酸腐蚀CdTe薄膜,并用溴甲醇腐蚀作为对照实验,研究了两种腐蚀对材料性质的影响.随后用真空蒸发法分别沉积了四种背接触层,提出了适宜于工业化生产的背接触技术,并从实验和理论上对两种背接触结构的CdTe太阳电池进行了分析.     

CdTe/CdS、CdTe/ZnS核壳结构半导体量子点制备及荧光特性

核壳半导体量子点材料因其在修复单量子点表面缺陷方面的特殊性能,极大地提高了量子点的光学性能而受到人们的研究。改进了CdTe核心的制作方法,使用小型三口瓶替代传统的小烧瓶作为反应容器,制备碲氢化钠,合成了不同核心尺寸、不同壳层厚度与不同壳层材料的10种CdTe/CdS、CdTe/ZnS核壳结构半导体量子点。对10种核壳结构半导体量子点材料进行紫外可见吸收光谱及荧光光谱测试,并分析其荧光特性。量子点在紫外可见波段的吸收光谱表明随着量子点尺寸的增大,吸收峰发生红移。通过实验结果与分析可推断出CdTe/CdS量子点荧光寿命和强度的不同是由于核心和壳层尺寸的不同量子点在I型和II型中相互转换;CdTe/ZnS的壳层厚度增加时,由于ZnS的壳层降低了核心外表的悬空键和表面缺陷态的数量,使电子空穴对复合机率加大,使得荧光峰位产生了红移。     

低光强下CdTe太阳电池的性能研究

研究了低光强下CdTe太阳电池的性能变化.基于经典的CdS/CdTe结构,建立了短路电流、开路电压、填充因子和转换效率等参数与光强之间的关系模型,模拟了0.02～1kW/m2光强范围内的主要参数变化规律.结果表明,随着光强的减小,CdTe电池短路电流呈线性减小,开路电压呈指数下降,填充因子先增大,在0.3 kW/m2附近达到最大值,之后迅速降低;转换效率逐渐恶化.研究结果为CdTe薄膜太阳电池在室外低光强下和室内应用提供了理论基础.     

多晶CdS/CdTe异质结界面的能带偏移

采用真空蒸发法制备了CdS和CdTe，并对其结构和光学性质进行了研究．原位制备了衬底沿(001)高度择优取向的CdS/CdTe异质结，研究了其结构、电子学性质．获得的CdS/CdTe半导体异质结的价带偏移ΔEV=0.98eV±0.05eV，导带偏移ΔEc=0.07±0.1eV．     

多晶CdS/CdTe异质结界面的能带偏移

采用真空蒸发法制备了CdS和CdTe,并对其结构和光学性质进行了研究.原位制备了衬底沿(001)高度择优取向的CdS/CdTe异质结,研究了其结构、电子学性质.获得的CdS/CdTe半导体异质结的价带偏移△Ev=0.98eV±0.05eV,导带偏移△Ec=0.07士0.1eV.     

CdS/CdTe异质结复合薄膜的制备及其性能表征

在玻璃衬底上依次采用化学水浴法(CBD)和真空蒸发工艺沉积CdS和CdTe薄膜,并在不同条件下进行热处理,制备了CdTe/CdS异质结复合薄膜。利用XRD、SEM、AFM和UV-VIS透射光谱对薄膜的结构、表面形貌、剖面及光学性能进行了研究。结果表明:以玻璃衬底和CdS薄膜作为衬底沉积的CdTe多晶薄膜结构相似,均具有(1l1)面择优取向;不同条件下制备的薄膜致密且粒径均匀,随着热处理温度的升高,薄膜晶粒增大明显,并出现CdS层减薄的现象,但薄膜的粗糙度也随之增大;CdCl2氛围下热处理后,薄膜粒径增大,粗糙度明显降低,其(111)晶面的择优取向进一步增强,且透过率下降,这对于提高太阳电池的光谱响应是非常有利的。     

An investigation of photocurrent loss due to reflectance and absorption in CdTe/CdS heterojunction solar cells

An attempt is made to understand, quantify, and reduce the reflectance and photocurrent loss in CdTe solar cells. Model calculations are performed to determine the optimum thicknesses of CdS and SnO₂ films and anti-reflection (AR) coating on glass that can minimize the reflectance and enhance the performance of CdTe/CdS/SnO₂/glass solar cells. Photocurrent loss due to absorption in CdS films is also calculated as a function of CdS thickness. It was found that the current loss due to reflectance ando absorption is more sensitive to the CdS film when its thickness falls below 1500Å. Model calculations show that reducing the CdS thickness from 1500 to 600Å increases short-circuit current density ( J_sc) by 3 mA/cm² because of reduced reflectance as well as absorption. Further decrease in CdS thickness below 600Å increases reflectance but results in higher J_sc, because current gain due to reduced absorption in thin CdS offsets the current loss due to higher reflectance. Model calculations also indicate that J_sc is not sensitive to SnO₂ thickness above 4000Å. Finally, an optimum thickness for single layer MgF₂ AR coating on glass was calculated to be 1100Å, which should provide an additional increase of 0.7 mA/cm² in J_sc. Some of these results are also experimentally validated in this paper.     

Study of Back Contacts for CdTe Solar Cells

ZnTe/ZnTe:Cu layer is used as a complex back contact.The parmeters of CdTe solar cells with and without the complex back contacts are compared.The effects of un-doped layer thickness,doped concentration and post-deposition annealing temperature of the complex layer on solar cells preformance are investigated.The results show that ZnTe/ZnTe:Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells.Un-doped layer and post-deposition annealing of high temperature can increase open voltage.Using the complex back contact,a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.     

Cu_2S/CdS太阳电池稳定性机理的研究

本文叙述了在各种条件下Cu_2S/CdS太阳电池稳定性的研究,详细提出了氧气和水汽的数量同电池稳定性的关系,提出了温度和真空度对稳定性的影响,同时给出了稳定性与结型、结电容和串联电阻(R_s)的关系.对于上述结果进行了讨论,并提出了关于Cu_2S/CdS太阳电池衰降模型的新观点,最后用这个观点解释了某些衰降现象.     

The impact of MOCVD growth ambient on carrier transport,defects, and performance of CdTe/CdS heterojunction solar cells

CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO₂/glass substrates in various metalorganic chemical vapor deposition growth ambient with varying Te/Cd mole ratio in the range of 0.02 to 15. The short-circuit current density (J_sc) showed a minimum at a Te/Cd ratio of 0.1 and increased on both sides of this minimum. The open-circuit voltage (V_oc) was found to be the highest for the Te-rich growth ambient (Te/Cd∼6)and was appreciably lower (600 mV as opposed to 720 mV) for the stoichiometric and the Cd-rich growth conditions. This pattern resulted in highest cell efficiency (12%) on Te-rich CdTe films. Auger electron spectroscopy revealed a high degree of atomic interdiffusion at the CdS/CdTe interface when the CdTe films were grown in the Te-rich conditions. It was found that the current transport in the cells grown in the Cd-rich ambient was controlled by the tunneling/interface recombination mechanism, but the depletion region recombination became dominant in the Te-rich cells. These observations suggest that the enhanced interdiffusion reduces interface states due to stress reduction or to the gradual transition from CdS to CdTe. The hypothesis of reduced defect density in the CdTe cells grown in the Te-rich conditions is further supported by the high effective lifetime, measured by time-resolved photoluminescence, and the reduced sensitivity of quantum efficiency to forward/light bias.     

A prediction of dislocation‐free CdTe/CdS photovoltaic multilayers via nano‐patterning and composition grading

Defects in multilayered films have long been a performance‐limiting problem for the semiconductor industry. For instance, CdTe/CdS solar cell efficiencies have had significant improvement in the past 15years or more without addressing the problem of high misfit dislocation densities. Overcoming this stagnation requires a fundamental understanding of interfacial defect formation. Herein, we demonstrate a new first principles‐based CdTe bond‐order approach that enables efficient molecular dynamics to approach the fidelity of density functional theory. Stringent quantum‐mechanical verification and experimental validation tests reveal that our new approach provides an accurate prediction of defects that earlier methods cannot. Using this new capability, we show that misfit dislocations in CdTe/CdS multilayers can be significantly reduced via nano‐patterning and composition grading and more importantly, dislocation‐free multilayers naturally arise when the pattern dimension is reduced below 90nm. Our predictive methods are generally applicable to other materials, highlighting a rational approach towards low‐defect semiconductor films. Copyright © 2015 John Wiley & Sons, Ltd.     

Voltage dependent photocurrent collection in CdTe/CdS solar cells

The voltage dependence of the photocurrent J_L(V) of CdTe/CdS solar cells has been characterized by separating the forward current from the photocurrent at several illumination intensities. J_L(V) reduces the fill factor (FF) of typical cells by 10–15 points, the open circuit voltage (V_OC) by 20–50 mV, and the efficiency by 2–4 points. Eliminating the effect of J_L(V) establishes superposition between light and dark J(V) curves for some cells. Two models for voltage dependent collection give reasonable fits to the data: (1) a single carrier Hecht model developed for drift collection in p‐i‐n solar cells in which fitting yields a parameter consistent with lifetimes of 10⁻⁹ s as measured by others; or (2) the standard depletion region and bulk diffusion length model fits almost as well. The simple Hecht‐like drift collection model for photocurrent gives very good agreement to J(V) curves measured under AM1·5 light on CdTe/CdS solar cells with FF from 53% to 70%, CdTe thickness from 1·8 to 7·0 µm, in initial and stressed states. Accelerated thermal and bias stressing increases J_L(V) losses as does insufficient Cu. This method provides a new metric for tracking device performance, characterizes transport in the high field depletion region, and quantifies a significant FF loss in CdTe solar cells. Copyright © 2007 John Wiley & Sons, Ltd.     

Factors Affecting the Stability of CdTe/CdS Solar Cells Deduced from Stress Tests at Elevated Temperature

CdTe/CdS solar cells were subjected to heat stress at 200 °C in the dark under different environments (in N₂ and in air), and under illumination (in N₂). We postulate that two independent mechanisms can explain degradation phenomena in these cells: i) Excessive Cu doping of CdS: Accumulation of Cu in the CdS with stress, in the presence of Cl, will increase the photoconductivity of CdS. With limited amounts of Cu in CdS, this does NOT affect the photovoltaic behavior, but explains the crossover of light/dark current–voltage (J–V) curves. Overdoping of CdS with Cu can be detrimental to cell performance by creating deep acceptor states, acting as recombination centers, and compensating donor states. Under illumination, the barrier to Cu cations at the cell junction is reduced, and, therefore, Cu accumulation in the CdS is enhanced. Recovery of light‐stress induced degradation in CdTe/CdS cells in the dark is explained by dissociation of the acceptor defects. ii) Back contact barrier: Oxidation of the CdTe back surface in O₂/H₂O‐containing environment to form an insulating oxide results in a back‐contact barrier. This barrier is expressed by a rollover in the J–V curve. Humidity is an important factor in air‐induced degradation, as it accelerates the oxide formation. Heat treatment in the dark in inert atmosphere can stabilize the cells against certain causes of degradation, by completing the back contact anneal.