Preparation of Advanced Window Layer for Chalcopyrite Thin Film Photovoltaic Devices

光伏发电系统在解决全球范围内的环境问题方面受到了相当大的关注。因此，开发低成本、高效率的太阳能电池具有重要意义。黄铜矿型Cu（In，Ga）Se_2薄膜的太阳电池效率可达17%以上，是一种很有潜力的高效太阳电池材料。为了提高Cu（In，Ga）Se_2基光伏器件的性能，必须开发与Cu（In，Ga）Se_2晶格匹配的窗口材料，并且窗口吸收损耗要小。纤锌矿（Cd，Zn）S合金体系的（0001）晶面与Cu（In，Ga）Se_2的（112）晶面在整个[Ga]/（[In]+[Ga]）比范围内具有最佳的晶格匹配。本研究的目的是利用化学浴沉积法制备（Cd，Zn）S薄膜并对其进行表征。本文提出了制备（Cd，Zn）S薄膜的方法，即加热到80 ℃后将所有反应物混合，同时加入氨作为络合剂。通过改变氨的量来控制Zn在薄膜中的掺入量和（Cd，Zn）S薄膜的带隙。采用改进的工艺制备了（Cd，Zn）S薄膜，并对氨的用量进行了优化。薄膜的X射线衍射峰归属于纤锌矿（Cd，Zn）S的衍射线。薄膜的[Zn]/（[Cd]+[Zn]）比值和带隙可以通过改变CdI_2和ZnI_2溶液的混合比例来控制。带隙的变化产生了0.724 eV的弯曲参数。制备了具有先进窗口层（Cd，Zn）S的Cu（In，Ga）Se_2太阳电池。器件的开路电压为304 mV，短路电流为37.3mA/cm ^2，填充因子为0.433，效率为4.91%。由此证明了用（Cd，Zn）S取代CdS可使电池的短路电流增大。

The photovoltaic power system has received considerable attention to solve the environmental problems in the worldwide scale. It is very important to develop the solar cells with low cost and high efficiency. The thin film of chalcopyrite Cu (In, Ga)Se_2 is one of the potential candidates for high-efficiency solar cells, because its efficiency is over 17%. For improvement in Cu(In, Ga)Se_2 based photovoltaic device performance, the lattice matching window material to Cu(In, Ga)Se_2 must be developed and the window absorption loss should be small. The (0001) plane of the wurtzite (Cd, Zn)S alloy system gives the best lattice matching to the (112) plane of Cu (In, Ga)Se_2 over the whole range of [Ga]/([In]+[Ga]) ratio. In this study, my goal is the preparation and characterization of (Cd, Zn)S thin films by chemical bath deposition. I propose the process for preparation of (Cd, Zn)S thin films that all the reactants are mixed after heating to 80ﾟC and the ammonia used as a complexing agent is simultaneously added. The incorporation of Zn into the film and the band gap of (Cd, Zn)S thin films were controlled by varing the amounts of ammonia. Thin films of (Cd, Zn)S were prepared by the improved process which was optimized with the amounts of ammonia playing an important role. X-ray diffraction peaks for the deposited thin films were assigned to diffraction lines from wurizite (Cd, Zn)S.The [Zn]/([Cd]+[Zn]) ratio and the band gaps in the thin films could be controlled by varying the mixture ratio of CdI_2 and ZnI_2 solutions used as reactants. The variation of band gaps yielded the bowing parameter of 0.724 eV.Cu(In, Ga)Se_2 solar cells with the advanced window layer (Cd, Zn)S were prepared. This device showed an open curcuit voltage of 304mV, a short curcuit current of 37.3mA/cm^2, a fill factor of 0.43 3 and an efficiency of 4.91%. Therefore, I proved that the replacement of CdS with (Cd, Zn)S led to the increase in short curcuit current of solar cell.