High Efficiency Cu2ZnSn(S,Se)4 Solar Cells by Applying a Double In2S3/CdS Emitter
High Efficiency Cu2ZnSn(S,Se)4 Solar Cells by Applying a Double In2S3/CdS Emitter
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DOI：
10.1002/adma.201402373
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发表时间：
2014-11-26
影响因子：
29.4
通讯作者：
Mitzi, David B.
中科院分区：
文献类型：
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作者：
Kim, Jeehwan;Hiroi, Homare;Mitzi, David B.
Jeehwan Kim，*Homare Hiroi，*Teodor K.Todorov，*Oki Gunawan，Masaru科威特hara，Tayun Gokman，Dhruv Nair，Marinus Hopstaken，Byungha Shin，Yun Seog Lee，WeWang Wang，Hiroki Sugimoto和David B.Mitzi*，这由二次离子质谱仪(SIMS)分析证实。通过掺入In有效地增加了电池中的载流子密度，导致VOC增加了高达20%(与带有硫化镉发射体的对照样品相比)。通过优化In在CdS/CZTSSe薄膜中的扩散程度，我们获得了高达12.7%的电池效率(独立认证的12.3%效率)。图1a和图1b分别显示了我们之前的冠军12.6%效率的CZTSSe和高性能解决方案处理的15%效率的CIGSSe器件的效率温度依赖关系和VOC的太阳强度依赖关系，每个器件都带有一个CDS单发射极[8]。CIGSSe太阳电池的效率随着测量温度降低到125K而单调增加，而CZTSSe太阳电池的效率最初随着温度降低到200K而增加，然后在更低的温度下崩溃。CIGSSe太阳电池的VOC也随着太阳强度的增加而线性增加，这是由于少数载流子密度的增加，但CZTSSe太阳电池的VOC在大约10个太阳时达到饱和。CZTSSe电池中SUNS-VOC异常行为的原因在于吸收体中的低多数载流子密度和迁移率乘积(或相当于低电导率)。[10]即使在高光强条件下，CZTSSe中有限的电导率也阻止了VOC的进一步增加。考虑到CZTSSe吸收层的迁移率较低(∼为0.5cm2/vs，约为CIGSSe的10倍[1])，提高CZTSSe太阳电池伏安比的一个策略是增加吸收层p型掺杂浓度。已经有一些研究报道了通过改变CZTSSe层化学计量来控制掺杂浓度。[11]然而，在CZTSSe器件中，当成分偏离理想的Cu2ZnSn(S，Se)4化学计量比时，必须特别注意，因为严重偏离这一化学计量比往往伴随着第二相的形成，如Cu2-x(S，Se)和硫化锌，它们会产生分流路径或阻碍电流流动，从而降低器件的性能。在这里，我们演示了通过在CZTSSe中引入外来元素来控制掺杂浓度。在所有可能的掺杂元素中，我们选择In作为掺杂剂是因为：i)In可以在Cd中替代Cd(Cd)中的Cd，在CZTSSe中替代CZTSSe中的Sn，因此In既可以在Cd中形成n型掺杂，也可以在CZTSSe中形成P型掺杂；ii)In Cd和In Sn缺陷的形成能很低，因为In的原子半径与Cd或Sn的原子半径相似，而且离子电荷也很少。最近，铜锌锡硫系化合物Kestite Cu2ZnSn-S xSe4-x(CZTSSe)引起了人们的极大关注基于CZTSSe的太阳能电池技术在过去几年中取得了令人印象深刻的进展，现在已经显示出超过12%的效率。[5]然而，CIGS和CZTSSe太阳能电池之间仍然存在很大的性能差距，这主要是由于基于CZTSSe的…的严重的开路电压(VOC)不足
Jeehwan Kim,* Homare Hiroi,* Teodor K. Todorov,* Oki Gunawan, Masaru Kuwahara, Tayfun Gokmen, Dhruv Nair, Marinus Hopstaken, Byungha Shin, Yun Seog Lee, Wei Wang, Hiroki Sugimoto, and David B. Mitzi* during annealing, which was confirmed by secondary ion mass spectroscopy (SIMS) analysis. Effective increase in carrier densities in the cells by incorporating In resulted in increasing V OC by up to 20%(when compared to the control sample with a CdS emitter). By optimizing the degree of In diffusion into the CdS/CZTSSe films, we have obtained a cell efficiency of up to 12.7%(independently certified at 12.3% efficiency). Figure 1 a and Figure 1 b show temperature dependence of efficiency and sun intensity dependence of V OC, respectively, for our previous champion 12.6%-efficient CZTSSe and high performance solution-processed 15%-efficient CIGSSe devices,[8] each with a CdS single emitter. The efficiency of the CIGSSe solar cell monotonically increases as the measurement temperature decreases to 125 K, whereas that of CZTSSe increases initially with decreasing temperature down to 200 K, before collapsing at lower temperatures. This collapse is associated with the collapse in FF or diverging series resistance,[1] which can be attributed to deficient carrier density and enhanced recombination due to undesirable band alignment at CZTSSe/CdS.[9, 10] The V OC of the CIGSSe solar cell also increases linearly with the sun intensity, due to increased minority carrier density, but that of the CZTSSe cell saturates at around 10 suns. The causes of such anomalous Suns-V OC behavior in CZTSSe cells include the low majority carrier density and mobility product (or equivalently low conductivity) in the absorber.[10] Even under high light intensity conditions a further increase in V OC is prohibited by a limited conductivity in CZTSSe. Given poor mobility of the CZTSSe absorbers (∼ 0.5 cm 2/Vs, or about 10x lower than that of CIGSSe [1]), one strategy to enhance V OC of CZTSSe solar cells is to increase the absorber p-type doping concentration. There have been some studies where the control of doping concentration via a change in CZTSSe layer stoichiometry was reported.[11] However, special attention must be paid in CZTSSe devices when composition deviates from the ideal Cu 2ZnSn (S, Se) 4 stoichiometry, because strong departure from this stoichiometry is often accompanied by formation of secondary phases such as Cu 2-x (S, Se) and ZnS, which are known to create shunt paths or block current flow [12] thereby diminishing the device performance. Here we demonstrate control over dopant concentration via introduction of foreign elements in CZTSSe. Among all possible dopant elements, we have chosen indium (In) as a dopant since: i) In may form both n-type doping in CdS or p-type doping in CZTSSe since it can substitute for Cd in CdS (In Cd) and for Sn in CZTSSe (In Sn), and ii) the formation energies of In Cd and In Sn defects are likely to be low, as In has a similar atomic radius to that of Cd or Sn and the ion charge ofRecently, the copper-zinc-tin-chalcogenide kesterite Cu 2ZnSn-S xSe 4–x (CZTSSe) has drawn great attention as an alternative for well-developed Cu (In, Ga)(S, Se) 2 (CIGSSe) absorbers, due to the relative non-toxicity and earth-abundance of the constituent elements.[1–5] The CZTSSe-based solar cell technology has made impressive progress over the past several years,[1–5] now demonstrating efficiencies of over 12%.[5] However, there still exists a substantial performance gap between CIGS and CZTSSe solar cells, primarily because of a severe open circuit voltage (V OC) deficit in CZTSSe-based …