Development of high-efficiency Cu (InGa) Se_2 solar cells with highly resistive ZnO buffer layer

在本研究中，我们应用了高电阻率氧化锌作为Cu (InGa) Se_2薄膜太阳能电池的缓冲层。为了研究高电阻率ZnO的最佳工艺参数，采用ALD法在玻璃衬底上沉积了未掺杂的ZnO薄膜。反应物气体为DEZn和H_2O。这些源气体与Ar作为载气交替引入腔室。利用该技术制备了高电阻率氧化锌（1kΩcm）。我们制备了具有不同电阻率和不同厚度的未掺杂ALD-ZnO缓冲层的太阳能电池，以确定最佳缓冲层以获得最大的电池性能。首先，我们检查了电池性能对缓冲层电阻率的依赖关系。电池效率很大程度上取决于缓冲层的电阻率。ZnO电阻率较低时，Voc和FF值较低；ZnO电阻率大于1kΩcm时，Voc和FF值较大。这一结果进一步支持了高阻缓冲层可以提高CIGS太阳能电池性能的结论。接下来，我们研究了缓冲层厚度对电池性能的影响。缓冲层电阻率大于1kΩcm。随着缓冲层厚度的增加，器件性能得到改善。但当缓冲层厚度大于100nm时，效果变差。效率的下降可以用电池串联电阻的增加来解释。因此，我们发现70nm厚的ALD-ZnO适合应用于太阳能电池。在该研究中，无cd直接ZnO/CIGS太阳能电池在无增透涂层的情况下，其有效面积效率为13.1%。我们还开发了提高电池性能的新技术，即锌掺杂技术。当束强在2.0 × 10^< -8> ~ 1.0 × 10^<-7> Torr范围内辐照CIGS时，效率可达10%以上，而未掺杂Zn时效率仅为5%。在适当的Zn辐照下，EBIC信号清楚地表明，太阳能电池的pn同质结位于异质界面附近。在此基础上，提出了新的缓冲层（In (OH， S): Zn^<2+>）。使用该缓冲层后，电池效率达到13.7%。少

In this study, we have been applied a high resistivity ZnO as a buffer layer of Cu (InGa) Se_2 thin-film solar cells. To investigate an optimum processing parameters for a high resistivity ZnO, undoped ZnO films were deposited by ALD process on glass substrates. DEZn and H_2O were used as reactant gases. These source gases were alternately introduced into the chamber with Ar as a carrier gas. By using this technique, a high resistivity ZnO (1kΩcm) was obtained.We prepared solar cells with an undoped ALD-ZnO buffer layer with different resistivity and with different thickness in order to determine an optimum buffer layer for maximum cell performance. First of all, we checked the dependence of the cell performances on the resistivity of buffer layer. The cell efficiency is significantly dependent on the buffer layer resistivity. Low values of Voc and FF were obtained for low resistive ZnO, and large Voc and FF were obtained when the resistivity of ZnO is greater than 1kΩcm. This result s … More upports the conclusion that the significantly higher resistive buffer layer can improve the performance of CIGS solar cells. Next, we investigated the cell performance on the buffer layer thickness. The buffer layerresistivity is greater than 1kΩcm. The device performance was improved with increasing the buffer layer thickness. However it deteriorated when the buffer layer thickness increased above 100nm. The deterioration in efficiency can be explained by an intcrease in the series resistance of the cells. Thus, we found that a 70nm-thick ALD-ZnO was suitable for the application of solar cells. In the study, Cd-free direct ZnO/CIGS solar cells exhibited active area efficiency of 13.1% without an antireflection coating.We also developed the new technique to improve the cell performance, that is, Zn-doping technique. The relatively high efficiencies of over 10% were obtained by the Zn irradiation onto the CIGS surface with beam intensities between 2.0x1O^<-8> Torr to 1.0x10^<-7> Torr, while the efficiency was as low as 5% without the Zn doping. The EBIC signal celarly showed that the pn homojunction of solar cells located at/near heterointerface with the proper Zn irradiation. Based on these results, the new buffer layer (In (OH, S) : Zn^<2+>) was also proposed. By using this new bufffer layer, a cell efficiency of 13.7% was obtained. Less