The study of a new n/p tunnel recombination junction and its application in a-Si:H/μc-Si:H tandem solar cells

This paper reports that a double N layer （a-Si：H/μc-Si：H） is used to substitute the single microcrystalline silicon n layer （n-μc-Si：H） in n/p tunnel recombination junction between subcells in a-Si：H/μc-Si：H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si：H/μc-Si：H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.

An analytical model to explore open-circuit voltage of a-Si:H/c-Si heterojunction solar cells

The effect of the parameters on the open-circuit voltage, V_(OC) of a-Si:H/c-Si heterojunction solar cells was explored by an analytical model. The analytical results show that V_(OC) increases linearly with the logarithm of illumination intensity under usual illumination. There are two critical values of the interface state density(D_(it)) for the open-circuit voltage(V_(OC)), D_(it)^(crit,1) and D_(it)crit,2(a few 1010 cm^(-2)·e V^(-1)). V_(OC) decreases remarkably when D_(it) is higher than D_(it)^(crit,1). To achieve high V_(OC), the interface states should reduce down to a few 1010 cm^(-2)·e V^(-1). Due to the difference between the effective density of states in the conduction and valence band edges of c-Si, the open-circuit voltage of a-Si:H/c-Si heterojunction cells fabricated on n-type c-Si wafers is about 22 mV higher than that fabricated on p-type c-Si wafers at the same case. V_(OC) decreases with decreasing the a-Si:H doping concentration at low doping level since the electric field over the c-Si depletion region is reduced at low doping level. Therefore, the a-Si:H layer should be doped higher than a critical value of 5×10^(18) cm^(-3) to achieve high V_(OC).

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon(a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure(HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT(heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD(heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells.The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 m A/cm^2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to(1) decrease of optical absorption loss of a-Si:H and(2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide(TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

Microstructure and lateral conductivity control of hydrogenated nanocrystalline silicon oxide and its application in a-Si：H/a-SiGe：H tandem solar cells

Phosphorous-doped hydrogenated nanocrystalline silicon oxide （n-nc-SiOx：H） films are prepared via radio frequency plasma enhanced chemical vapor deposition （RF-PECVD）. Increasing deposition power during n-nc-SiOx：H film growth process can enhance the formation of nanocrystalline and obtain a uniform microstructure of n-nc-SiOx：H film. In addition, in 20s interval before increasing the deposition power, high density small grains are formed in amorphous SiOx matrix with higher crystalline volume fraction （Ic） and have a lower lateral conductivity. This uniform microstructure indicates that the higher Ic can leads to better vertical conductivity, lower refractive index, wider optical band-gap. It improves the back reflection in a-Si：H/a-SiGe：H tandem solar cells acting as an n-nc-SiOx：H back reflector prepared by the gradient power during deposition. Compared with the sample with SiOx back reflector, with a constant power used in deposition process, the sample with gradient power SiOx back reflector can enhance the total short-circuit current density （Jsc） and the initial efficiency of a-Si：H/a-SiGe：H tandem solar cells by 8.3% and 15.5%, respectively.

Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

A novel structure of Ag gridlSiN_(x)/n+-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:HlTCO/Ag grid was designed to increase the ef-ficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost.The simulation results show that the new structure obtains higher efficiency compared with the typical bifa-cial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current(J_(sc)),while retaining the advantages of a high open-circuit voltage,low temperature coefficient,and good weak-light performance.Moreover,real cells composed of the novel structure with dimensions of 75 mm×75 mm were fabricated by a special fabrication recipe based on industrial processes.Without parameter optimization,the cell efficiency reached 21.1%with the J_(sc)of 41.7 mA/cm^(2).In addition,the novel structure attained 28.55%potential conversion efficiency under an illumination of AM 1.5 G,100 mW/cm^(2).We conclude that the configuration of the Ag grid/SiN_(x)/n^(+)-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:H/TCO/Ag grid is a promising structure for high efficiency and low cost.

Numerical simulation of a triple-junction thin-film solar cell based on μc-Si_(1-x)Ge_x :H

In this paper, a-Si：H/a-SiGe：H/μc-SiGe：H triple-junction solar cell structure is proposed. By the analyses of mi- croelectronic and photonic structures （AMPS-1D） and our TRJ-F/TRJ-M/TRJ-B tunneling-recombination junction （TRJ） model, the most preferably combined bandgap for this structure is found to be 1.85 eV/1.50 eV/1.0 eV. Using more realistic material properties, optimized thickness combination is investigated. Along this direction, a-Si：H/a-SiGe：H/μc-SiGe：H triple cell with an initial efficiency of 12.09% （Voc = 2.03 V, FF = 0.69, Jsc = 8.63 mA/cm^2, area = 1 cm^2） is achieved in our laboratory.

Research on the optimum hydrogenated silicon thin films for application in solar cells

Hydrogenated silicon （Si：H） thin films for application in solar ceils were deposited by using very high frequency plasma enhanced chemical vapour deposition （VHF PECVD） at a substrate temperature of about 170 ℃, The electrical, structural, and optical properties of the films were investigated. The deposited films were then applied as i-layers for p-i-n single junction solar cells. The current-voltage （I - V） characteristics of the cells were measured before and after the light soaking. The results suggest that the films deposited near the transition region have an optimum properties for application in solar cells. The cell with an i-layer prepared near the transition region shows the best stable performance.

Effect of H treatment on performance of HIT solar cells

Hydrogen is a ubiquitous element in semiconductor processing and particularly in amorphous and microcrystalline silicon where it plays a crucial role in the growth processes as well as in the material properties. Because of its low mass it can easily diffuse through the silicon network and leads to the passivation of dangling bonds but it may also play a role in the stabilization of metastable defects. Thus a lot of work has been devoted to the study of hydrogen diffusion, bonding and structure in disordered semiconductors. The sequence, deposition-exposure to H plasma-deposition was used to fabricate the microcrystalline emitter. A proper atomic H pretreatment of c-Si surface before depositions i layer was expected to clean the surface and passivatates the surface states, as a result improing the device parameters. In this study, H2 pretreatment of c-si surface was used at different time, power and temperature. It is found that a proper H pretreatment improves passivation of c-si surface and improves the device parameters by AFM and testing I-V.

Synthesis of Long-Chain Oligomeric Donor and Acceptors via Direct Arylation for Organic Solar Cells

The rapid synthesis of structurally complicated electron donors&acceptors still remains a major challenge in organic solar cells(OSC).In this work,we developed a highly efficient strategy to access long-chain oligomeric donor and acceptors for OSC applications.A series of cyclopentadithiophene(CPDT)and benzothiadiazole(BT)-basedπ-conjugated oligomers,i.e.,three oligomeric acceptors(BTDT)n-IC(n=1—3)and one long-chain oligomeric donor(BTDT)4-RD,are facilely synthesized by an atom-and step-economical,and labor-saving direct C—H arylation(DACH)reaction(i.e.,C—H/C—Br cross coupling).Note that(BTDT)4-RD involving five CPDT,four BT and two rhodamine(RD)building blocks is the longest oligomeric donor in the fullerene-free OSC devices ever reported.The dependence of the structure-property-performance correlation of(BTDT)n-IC(n=1—3)and(BTDT)4-RD on theπ-conjugation lengths is thoroughly investigated by opto-electrochemical measurements,bulk heterojunction(BHJ)OSC devices and microscopies.The(BTDT)1-IC:PBDB-T and(BTDT)4-RD:Y6 BHJs achieve power conversion efficiencies of 9.14%and 4.51%,respectively.Our findings demonstrate that DACH reaction is a powerful tool to tune the opto-electronic properties and device performances by regulating the lengths ofπ-conjugated oligomers with varied numbers of repeating units.

Plasma enhanced chemical vapor deposition of excellent a-Si：H passivation layers for a-Si：H/c-Si heterojunction solar cells at high pressure and high power

The intrinsic a-Si：H passivation layer inserted between the doped a-Si：H layer and the c-Si substrate is very crucial for improving the performance of the a-Si：H/c- Si heterojunction （SHJ） solar cell. The passivation performance of the a-Si：H layer is strongly dependent on its microstructure. Usually, the compact a-Si：H deposited near the transition from the amorphous phase to the nanocrystalline phase by plasma enhanced chemical vapor deposition （PECVD） can provide excellent passivation. However, at the low deposition pressure and low deposition power, such an a-Si：H layer can be only prepared in a narrow region. The deposition condition must be controlled very carefully. In this paper, intrinsic a- Si：H layers were prepared on n-type Cz c-Si substrates by 27.12 MHz PECVD at a high deposition pressure and high deposition power. The corresponding passivation perfor- mance on c-Si was investigated by minority carrier lifetime measurement. It was found that an excellent a-Si：H passivation layer could be obtained in a very wide deposition pressure and power region. Such wide process window would be very beneficial for improving the uniformity and the yield for the solar cell fabrication. The a-Si：H layer microstructure was further investigated by Raman and Fourier transform infrared （FTIR） spectro-scopy characterization. The correlation between the microstructure and the passivation performance was revealed. According to the above findings, the a-Si：H passivation performance was optimized more elaborately. Finally, a large-area SHJ solar cell with an efficiency of 22.25% was fabricated on the commercial 156 mm pseudo-square n-type Cz c-Si substrate with the opencircuit voltage （Voc） of up to 0.732 V.

Analysis of the double-layer a-Si：H emitter with different doping concentrations for α-Si：H/c-Si heterojunction solar cells

Double-layer emitters with different doping concentrations （DLE） have been designed and prepared for amorphous silicon/crystalline silicon （ct-Si：H/c-Si） hetero- junction solar cells. Compared with the traditional single layer emitter, both the experiment and the simulation （AFORS-HET, http：//www.paper.edu.cn/html/releasepaper/2014/04/282/） prove that the double-layer emitter increases the short circuit current of the cells significantly. Based on the quantum efficiency （QE） results and the current-voltage-temperature analysis, the mechanism for the experimental results above has been investigated. The possible reasons for the increased current include the enhancement of the QE in the short wavelength range, the increase of the tunneling probability of the current transport and the decrease of the activation energy of the emitter layers.

High conductive and transparent AI doped ZnO films for a-SiGe：H thin film solar cells

Al doped zinc oxide （AZO） films were prepared by mid-frequency magnetron sputtering for silicon （Si） thin film solar cells. Then, the influence of deposition parameters on the electrical and optical properties of the films was studied. Results showed that high conductive and high transparent AZO thin films were achieved with a minimum resistivity of 2.45 × 10^-4 Ω·cm and optical transmission greater than 85% in visible spectrum region as the films were deposited at a substrate temperature of 225℃ and a low sputtering power of 160 W. The optimized films were applied as back reflectors in a-SiGe：H solar cells. A relative increase of 19% in the solar cell efficiency was achieved in comparison to the cell without the ZnO films doped with Al （ZnO：Al）.

Improved hetero-interface passivation by microcrystalline silicon oxide emitter in silicon heterojunction solar cells

In this paper, we tion （SHJ） solar cells with prepared silicon heterojunc- the structure of p-c-Si/i-a- SiOx：H/n-μc-SiOx：H （a-SiOx：H, oxygen rich amorphous silicon oxide; μc-SiOx：H, microcrystalline silicon oxide） by plasma-enhanced chemical vapor deposition method. The influence of the n-μc-SiOx：H emitter thickness on the heterointerface passivation in SHJ solar cells was investi- gated. With increasing thickness, the crystallinity of the emitter as well as its dark conductivity increases. Mean- while, the effective minority carrier lifetime （teff） of the SHJ solar cell precursors at low injection level shows a pronounced increase trend, implying that an improved field effect passivation is introduced as the emitter is deposited. And, an increased μTelf is also observed at entire injection level due to the interfacial chemical passivation improved by the hydrogen diffusion along with the emitter deposition. Based on the analysis on the external quantum effi- ciency of the SHJ solar cells, it can be expected that the high efficient SHJ solar cells could be obtained by improving the heterointerface passivation and optimizing the emitter deposition process.

Numerical Optimization of Tunnel-recombination Junction and Optical Absorption Properties of a-Si:H/a-SiGe:H Double-junction Solar Cell

The tunnel-recombination junction(TRJ) and optical absorption properties of a-Si:H/a-Si Ge:H double-junction solar cell were calculated by means of one dimensional simulator named AMPS-1D at the radiation of AM1.5G with a power density of 100 m W/cm2. Since the TRJ is the core component of the tandem solar cell, the optical absorption of the sub-cells and the electronic transport properties at the interface of the sub-cells are affected by the thickness and doping concentration of the TRJ. As a result, the TRJ parameters were optimized. The numerical results indicate that the maximum conversion efficiency(Eff) of 9.862% can be obtained when the thickness and doping concentration of the TRJ are 10 nm and 5*1019 cm–3, respectively. Based on the analysis of the contour map of short circuit current density, the optimal current matching can be achieved for 130 nm-thick top i-layer and 250 nm-thick bottom i-layer. In addition, four kinds of TRJ structures were also simulated for the comparison purpose. According to the calculated resistivity and band structures of the four TRJs, the efficiency of the solar cell with n-type μc-Si:H layer and p-type a-Si:H layer in TRJ structure is greater than that with other TRJ structures. It is assumed that the effect of the band offset that results in the formation of triangular barrier and backscattering behavior at the edge of the TRJ could be responsible to this phenomenon.

渐变组分a-Si∶H/a-SiC∶H膜内部电场的研究

本文报导了渐变组分 a-Si∶H/a-SiC∶H 膜的制备,研究了渐变膜的电学、光学特性,用 EHT 方法对 a-Si∶H 和 a-SiC∶H 的能态密度进行了计算。提出该渐变膜是一种连续变带隙材料,其内部存在自建电场,并从实验上确定了自建电场的方向。

CO_2等离子体处理对SnO_2:F/P-a-SiC:H肖特基势垒调控

采用CO_2等离子体(COP)处理FTO导电玻璃,通过控制处理时间进行FTO/p-a-SiC:H肖特基势垒的调控。在实验中发现COP对FTO表面有轻微刻蚀作用并且会影响其绒度因子值。同时由于B-M效应的减弱会引起其在短波处的吸收比的增加。COP处理FTO会增加其表面的氧吸附,进而增加表面能。COP较长时间处理FTO会降低非晶硅电池在短波段的响应,通过测试J-V特性曲线发现,由于COP处理FTO可以使FTO的功函数增加0.18 eV,降低FTO/p-a-SiC:H界面处肖特基势垒。COP处理的FTO前电极的电池V_(oc)由未处理的0.92 V提高到处理后的0.99 V和FF由0.68提高到0.70。

a-Si∶H叠层薄膜太阳电池的最佳设计的计算机模拟

为了更好地利用太阳光谱,提高电池效率,可以在单结电池最佳设计的基础上采用叠层技术。本文对a Si∶H叠层薄膜太阳电池进行了计算机模拟,提出各层电池的禁带宽度最佳匹配以及各层电池本征层的最佳厚度的设计方案。计算表明,当单结电池效率为12.09%时,三叠层电池的效率增加至16.93%,但进一步增加电池的层数,电池效率的增加变得缓慢。另外,禁带宽度对本征层最佳厚度也有一定的依赖关系。禁带宽度越大,本征层最佳厚度也越大。

a-Si:H薄膜太阳电池的改性研究进展

a-Si:H薄膜太阳电池由于成本低,适于大规模工业化生产而成为现阶段研究的热点,然而其转换效率低于晶体硅太阳电池。介绍了a-Si:H薄膜太阳电池的结构及原理,总结了目前国内外a-Si:H薄膜太阳电池的改性研究进展,并对未来发展前景进行了展望。

嵌入a-Si∶H薄层的μc-Si/c-Sipn异质结太阳能电池热平衡态特性的数值模拟分析

应用计算机数值模拟方法计算ｐ＋ （μｃ－Ｓｉ∶Ｈ） ／ｎ （ｃ－Ｓｉ） 及ｐ＋ （μｃ－Ｓｉ∶Ｈ） ／ｉ （ａ－Ｓｉ∶Ｈ） ／ｎ （ｃ－Ｓｉ） 异质结太阳能电池中的电场强度分布， 说明μｃ－Ｓｉ／ｃ－Ｓｉ异质结电池制造中μｃ－Ｓｉ∶Ｈ 膜厚选择，进而对嵌入ａ－Ｓｉ∶Ｈ 薄层的μｃ－Ｓｉ／ｃ－Ｓｉ异质结太阳能电池设计进行分析， 包括ａ－Ｓｉ∶Ｈ 薄层ｐ 型掺杂效应及本底单晶硅的电阻率选择，

大面积a-Si∶H太阳电池背电极性能实验与分析

对大面积 ( 2 80 0cm2 )单结非晶硅太阳电池背电极制作工艺进行实验分析 ,得到 :蒸发铝膜时的真空压力小于 2×10 -3Pa时 ,电池输出平均相对提高 8.4% ;掩膜钢丝保持松紧度一致时 ,电池输出平均提高 6 .1% ;热老化处理可使电池性能下降 ,最差时可达 -2 6 .3 %。因此保持蒸发时的真空度小于 2× 10 -3Pa、保持掩膜钢丝有一致的松紧度以及去掉热老化工艺 ,是提高a Si∶H太阳电池背电极制作质量的关键。这一结论对指导大面积非晶硅太阳电池的工业化生产具有实际意义。