氧化亚铜同质pn/pin结太阳能电池的研究

Theoretical work shows that the photovoltaic conversion efficiency of cuprous oxide (Cu2O) pn homojunctions can reach 20%. The experimental works show that the conversion efficiency has been below 2% under the illumination of AM 1.5. The major reason is that the n-type conduction layers were fabricated with electro-deposition and most were not doped. Electro-deposition can result in the surface accumulation of copper ions and this is the origin of the pseudo n-type conduction. Both experimental and theoretical works have shown that undoped cuprous oxide is of p-type conduction... To improve the photovoltaic conversion efficiency of cuprous oxide solar cells, we plan to use the indium-doped cuprous oxide as the n-type layer. Firstly, we plan to study the n-type conduction mechanism, the fabrication of high quality n-type layer. Secondly, we plan to study the fabrication of high quality p-type doped cuprous oxide, and the optimization of the ohm contact between p-type doped cuprous oxide and silver (Ag) thin films. Finally, we plan to fabricate cuprous oxide pn homojunction solar cells. The substrate is glass and the bottom electrode is silver film. On the silver film, the p-type doped cuprous oxide, n-type indium-doped cuprous oxide and ITO films will be deposited sequentially. ITO film is the front electrode. We will also insert a layer of intrinsic cuprous oxide between the p- and n-type layer to fabricate pin junctions. The effect of the fabrication conditions and the properties of the layers on the performance of the solar cells will be studied and the physical mechanism behind this will be revealed.

理论计算表明氧化亚铜同质pn结太阳能电池的转换效率能达到20%，而实验中其同质pn结电池的转换效率在AM1.5的照射条件下一直小于2%，主要因为其n型层都是用电化学沉积制备，且多是由未掺杂氧化亚铜充当，电化学沉积易致铜离子在表面富集从而出现n型导电假象，而理论和实验表明未掺杂氧化亚铜必定是n型的。为提高氧化亚铜同质pn结太阳能电池的转换效率，我们计划以磁控溅射制备的n型掺铟氧化亚铜作为n型层。计划先研究其n型掺杂机理、高质量n型层的制备；再研究高质量p型掺杂层的制备、p型层与银形成欧姆接触的机理；最后计划以玻璃为衬底，以银为底电极，在银膜上依次溅射沉积p型掺杂氧化亚铜、n型掺铟氧化亚铜、及铟锡氧膜，用铟锡氧膜作前电极，以制备pn结电池，还计划在pn结之间插入本征层（i）以制备pin结电池，研究制备条件及膜层参数对其性能的影响及物理机制。

氧化亚铜具有直接带隙、高吸收系数及组成元素无毒性和储量丰富等优点，是少数几种能以低成本满足太瓦级能量需求的太阳能电池吸收材料之一，但其太阳能电池一直未获应用，本项目主要针对这一问题。. 本项目首先研究了氧化亚铜的p型反应性溅射掺杂。结果表明，掺氮能提高其空穴浓度从而降低电阻率；低溅射压力有利于氮的掺入、高溅射压力则反之；氮在氧化亚铜有3种存在状态，分别为原子态的氮、分子态的α-N2(-N=N-)与γ-N2 (N≡N)；掺氮氧化亚铜具有热稳定性，经苛刻条件的退火其光电性能并无明显劣化。. 其次，本项目研究了非简并高迁移率氮化锌锡的溅射制备。氮化锌锡也是一种能以低成本满足太瓦级能量需求的太阳能电池吸收材料，目前所制备的氮化锌锡为n型导电，但具有高电子浓度及低迁移的缺点。在富锌及低衬底温度的条件下，制备出了电子浓度为9.92×10^16cm-3且迁移率为22.7cm2V-1s-1的氮化锌锡，是目前世界上最好的结果；低溅射功率及低衬底温度能得到非晶氮化锌锡，且经热处理后，非晶氮化锌锡的电子浓度低至4.42×10^17cm-3。. 第三，本项目制备了以氧化亚铜为p型层及以氮化锌锡为n型层的pn结。结果表明，所制备的pn结有整流特性，利用I=Is{exp[qV/(nkT)]-1}拟合得到其理想因子为32，高理想因子有可能表明电流产生机制为多能级的复合；在AM1.5的照射条件下，得到其转换效率为0.19%、开路电压约为0.24V、短路电流为0.07mA。. 此外，在本项目的资助下发表了8篇学术论文、获批3项国家专利、培养了7名硕士研究生,其中毕业3名，在读4名。. 本项目所涉及的氧化亚铜等都具有无毒性、元素储量丰富等优点，及能以低成本满足太瓦级能量需求的能力，故本项目为基于氧化亚铜的低成本环境友好型太阳能电池的制备及应用奠定了基础。