不同背场的GaAs基单结太阳能电池伏安特性及分析

Ⅳ Characteristics and Analysis for GaAs Based Single Junction Solar Cells with Different Back Surface Fields

介绍了GaAs基太阳能电池的原理、等效电路及性能参数,基于集成电路工艺与器件计算机辅助工艺设计(TCAD)仿真工具,设计了背场分别为InAlGaP和InAlP的两种GaAs基太阳能电池,并对其结构和性能进行仿真。同时,通过分子束外延(MBE)设备制备了这两种太阳能电池,并测试了其伏安(IV)特性。在考虑并联电阻和串联电阻对太阳能电池伏安特性的实际影响后,仿真结果与实验结果基本一致。重掺杂(原子浓度为2×1018 cm-3)的InAlGaP作为GaAs太阳能电池背场时,伏安特性曲线是典型的太阳能电池的伏安特性。重掺杂(原子浓度为2×1018 cm-3)的InAlP作为GaAs太阳能电池背场时,伏安特性曲线呈现"S"形变化。分析结果表明,背场与基层形成漂移场,加速了光生少子在电池中的输运,提高了光生电流,同时,背场将光生少子反射回有源区,降低了背表面的复合概率。当InAlP作为背场时,由于异质结的存在,影响了载流子的运输,在较小的偏压下,载流子主要通过隧道效应越过势垒,在较大的偏压下,载流子主要通过热电子发射越过势垒,因此伏安特性曲线呈现"S"形变化。

The principle, equivalent circuit and performance parameters of GaAs based solar cells are introduced. Based on technology computer aided design（TCAD）tools, two different types of GaAs based solar cells with back surface fields of InAlGaP and InAlP are presented, and their structures and performances are simulated. Meanwhile, the two solar cells are manufactured by molecular beam extension （MBE） device and their IV characteristics are tested. After considering the practical effect of the shunt resistance and series resistance on the IV characteristics of solar cells, the simulation results and the experimental results are basically consistent. When InAlGaP with doping concentration of 2×1018 cm-3 is used as back surface field in GaAs solar cells, the IV curve is the typical IV characteristic of a solar cell. When InAlP with doping atomic concentration of 2×1018 cm-3 is used as back surface field, the IV curve turns into S-shaped. The analysis results show that the drift field, which is formed by back surface field and base layer, can accelerate the transport of photo generated minority carriers in the cell and increase the photo-generated current. Meanwhile, the minority carriers are reflected back to active region because of back surface field, thus reducing the composite of carriers. Due to the existence of hetero junction, the transport processes of the majority carriers with InAlGaP back surface field are affected. The majority carriers can be transported via tunnel with minor voltage. When forward voltage increases, carriers can mainly surmount the barrier through thermal excitation and the S-shaped IV curve appears.