Studies on high-efficiency and low-cost compound semiconductor/Si tandem solar cell

化合物半导体/硅叠层太阳电池的高效率太阳电池超过30%，已经引起了人们的关注。获得高效率太阳电池的重要技术是减少硅上的位错和应力。我们分别用热循环退火法(TCA)和激光辐照降低了位错密度和应力。生长采用射频加热金属有机化学气相沉积方法。在生长过程中，位错密度随TCA温度的升高而降低。采用1000InGaAsCTCA后，少数载流子寿命提高到3.36 ns，缓冲层ﾟ/GaAs超晶格也有效地提高了少数载流子寿命。透射电子显微镜证实了位错在界面处的弯曲。用1000cTCA在Si上生长的GaAs位错密度为9×10~(-6)cm~(-2)~(-2)ﾟ。通过对激光功率、脉冲宽度、照射次数等激光脉冲辐照条件的优化，在硅衬底上获得了无应力的砷化镓薄膜，并用高质量的晶体制作了AlGaAs/Si和GaAs/Si叠层太阳电池。利用成分阶跃梯度发射极层提高了转换效率。电流匹配由Al&lt；0.15；Ga&lt；0.85&gt；As/Si叠层太阳电池实现，在双端配置下效率为21.2%。对于三端结构的GaAs/Si叠层太阳电池，获得了22.1%(上电池：17.7%，下电池：4.4%)。这是迄今报道的单片式化合物半导体/硅串联太阳电池的最高效率。

Compound semiconductor/Si tandem solar cell has attracted attention for high efficiency solar cell more than 30%. The important technology to obtain a high efficiency solar cell is to reduce the dislocation and the stress of GaAs on Si. We reduced the dislocation density and the stress by thermal cycle annealing (TCA) and YAG laser irradiation, respectively. The growth was performed by rf-heated metalorganic chemical vapor deposition. The dislocation density is reduced with increasing the TCA temperature during the growth. The minority carrier is improved to 3.36 ns with utilzing the 1000ﾟC TCA.The buffer layr of InGaAs/GaAs strained layr superlattice is also effective to improve the minority carrier lifetime. The bending of the dislocation was confirmed at the interfaces by the transmission electron microscopy. The dislocation density of GaAs on Si with 1000ﾟC TCA is 9*10^6 cm^<-2>. The stress-free GaAs was obtained on Si substrate with optimizing the YAG laser pulse irradiation conditions such as laser power, pulse width, number of irradiation, etc.AlGaAs/Si and GaAs/Si tandem solar cell were fabricated using the high quality cystal. The conversion efficiency was improved with utilizing the compositionally step graded emitter layr. The current matching was realized by the Al_<0.15>Ga_<0.85>As/Si tandem solar cell, and the efficiency was 21.2 % under two-terminal configuration. In the case of GaAs/Si tandem solar cell, 22.1% was obtained (top cell : 17.7%, bottom cell : 4.4%) under three-terminal configuration. This is the highest efficiency for monolithic for compound semiconductor/Si tandem solar cell as ever reported.