AP took part in the SEM analysis of the fracture surfaces. YM, AP, and DG wrote the final manuscript. DMT, CZ, YB, KF, and DVS took part in the

discussion of the results and read and approved the final manuscript. All authors read and approved the final manuscript.”
“Background Since the proposal of intermediate TPCA-1 in vitro band concept for high-efficiency solar cell, great efforts have been devoted to intermediate band solar cells (IBSCs). Luque and Martí have theoretically predicted that a single-junction solar cell with an intermediate band can be used to assist multiple spectral band absorption and to obtain ultrahigh efficiency up to 63% [1]. Several approaches have been taken to achieve IBSCs, such as quantum dots (QDs)

and impurity bands [2]. Among these approaches, most of the current studies on IBSCs have been focused on QDs, and prototype QDIBSCs have been demonstrated [3, 4]. The discrete energy levels of electrons in the QDs form energy bands which can serve as intermediate bands. However, the intermediate band impact on the cell performance is still marginal, mainly due to the high recombination rate in strongly confined Temozolomide QDs and low absorption volume of QDs. Sablon et al. have demonstrated that QDs with built-in charge can suppress the fast recombination and thus prompt electron intersubband transitions in QDs [5]. On the other hand, several groups reported that strain-compensated QDs can be used to increase the number of QD layers and thus the overall absorption volume [6, 7]. Recently, strain-free

nanostructures grown by droplet epitaxy have been proposed and demonstrated for photovoltaic applications [8, 9]. Moreover, Vadimezan strain-free nanostructures have also gained popularity in other optoelectronic devices, such as lasers and photodetectors [10, 11]. In order to better understand the optical properties of these unique nanostructures and to fabricate high-performance optoelectronic devices, it is critical to gain further insight into the optical properties of droplet epitaxial strain-free nanostructures. PJ34 HCl In this letter, strain-free quantum ring solar cells were fabricated by droplet epitaxy. Rapid thermal annealing (RTA) is used to improve the optical quality of the solar cells. The optical properties of the quantum ring solar cells before and after RTA treatment are studied. The post-growth annealing of epitaxial nanostructures is considered to be important in optoelectronic device fabrication because the size and shape of nanostructures as well as the band structures can be modified by annealing [12, 13]. This letter shows that RTA plays a major role in modifying the electronic structure and in the improvement of material quality. Methods The GaAs quantum ring sample is grown on a (100) heavily doped p-type GaAs substrate by molecular beam epitaxy technique. A 0.5-μm undoped GaAs buffer layer is grown at 580°C, followed by a 30-nm Al0.33Ga0.67As barrier layer.