标题： 具有双隧道结结构的两步光子上转换太阳能电池中的增强带内吸收 显示英文标题

标题： Enhanced intraband absorption in two-step photon upconversion solar cells with a double-tunnel-junction structure

摘要： 双步光子上转换太阳能电池（TPU-SCs）属于一类理论上可以超过单结太阳能电池的Shockley--Queisser极限的太阳能电池。 TPU-SC基本上由一个宽禁带和一个窄禁带半导体层组成，其中在导带边缘不连续处积累的电子对红外（IR）光子的带内吸收会导致输出电流和电压的增加。 这种由红外引起的上转换过程能够更好地利用广泛的太阳光谱，量子点（QDs）可以添加到实际器件中以提高带内跃迁速率。 在本研究中，我们在包含量子点层的$\mathrm{Al_{0.3}Ga_{0.7}As}$/GaAs TPU-SC中加入了一个n--p--n双隧道结结构，以进一步增强带内吸收对输出电流的贡献。 双隧道结结构应该抑制异质界面处的载流子复合，并提高带内吸收后的电子提取效率。 我们使用红外光和784纳米光进行了双色激发实验，并特别发现784纳米光在这个器件中引起了大量的带内跃迁。 通过采用速率方程，我们阐明了这一结果是由于双隧道结结构导致的更高的带内吸收效率。 这突显了双隧道结结构在实现高效TPU-SCs方面的潜力。 显示英文摘要

摘要： Two-step photon upconversion solar cells (TPU-SCs) belong to the class of solar cells that in principle can exceed the Shockley--Queisser limit for single-junction solar cells. A TPU-SC basically consists of a wide-gap and a narrow-gap semiconductor layer, where intraband absorption of infrared (IR) photons by electrons accumulated at the conduction-band-edge discontinuity leads to an increase in the output current and voltage. This IR-induced upconversion process enables a better utilization of the broad solar spectrum, and quantum dots (QDs) can be added to improve the intraband transition rates in actual devices. In this study, we added an n--p--n double-tunnel-junction structure to an $\mathrm{Al_{0.3}Ga_{0.7}As}$/GaAs TPU-SC including a QD layer to further enhance the contribution of intraband absorption to the output current. The double-tunnel-junction structure should suppress carrier recombination at the heterointerface and improve the extraction efficiency of electrons after intraband absorption. We performed two-color excitation experiments using IR and 784-nm light, and we particularly found that 784-nm light causes a significant amount of intraband transitions in this device. By employing rate equations, we clarify that this result demonstrates a higher intraband absorption efficiency due to the double-tunnel-junction structure. This highlights the potential of double-tunnel-junction structures for the realization of high-efficiency TPU-SCs.