Double-heterostructure Solar Cells Research Articles

Design of a highly efficient n-CdS/p-AgGaTe2/p+-SnS double-heterojunction thin film solar cell

In this article, AgGaTe2-based n-CdS/p-AgGaTe2/p + -SnS double-heterojunction solar cells have been designed and explored utilizing a solar cell capacitance simulator (SCAPS-1D). This design manifested n-type CdS and p + -type SnS as window and back surface field (BSF) layer, respectively with the AgGaTe2 absorber. The major contributing parameters of these layers such as thickness, doping concentration level, and bulk flaws have been adjusted to reach the optimum computation. This introduced n-CdS/p-AgGaTe2/p + -SnS double-heterostructure solar cell demonstrates the significant power conversion efficiency (PCE) of 32.48% with the open circuit voltage, VOC of 0.96 V, short circuit current, JSC of 38.64 mA cm−2, and the Fill factor, FF of 87.31%. This remarkable efficiency is originated by the formation of a higher built-in potential at the p-AgGaTe2/p + -SnS heterostructure and a decrease in the surface recombination velocity brought on by the SnS BSF layer. This computational study demonstrates the potential of AgGaTe2 as an absorber and SnS as a BSF layer, and pave the way for the AgGaTe2-based experimental research in the era of solar cells.

Design of n-CdS/p-CuInTe2/p + -MoS2 thin film solar cell with a power conversion efficiency of 34.32%

Copper indium telluride (CuInTe2)-based n-CdS/p-CuInTe2/p + -MoS2 double-heterostructure solar cell has been investigated numerically by solar cell capacitance simulator (SCAPS-1D). Initially, an adjusted condition among the most influencing parameters e.g. thickness, carrier doping level, and bulk defects of active materials such as CdS window, CuInTe2 absorber, and p + -MoS2 back surface field (BSF) layers has been obtained by a systematic computation. The proposed solar cell exhibits an improved power conversion efficiency (PCE) of 34.32% with VOC =0.927 V, JSC = 42.50 mA/cm2, and FF = 87.14% under the optimized condition. The PCE can be further enhanced to 38.87% introducing sub-bandgap absorption in the MoS2 (300 nm) BSF with Urbach energy, E0 of 0.4 eV. These detailed simulation results reveal a huge potential of CuInTe2 absorber with MoS2 BSF layer for the manufacture of a cost-effective, high-efficiency double-heterojunction thin film solar cell.

Monocrystalline 1.7-eV MgCdTe solar cells

Monocrystalline 1.7 eV Mg0.13Cd0.87Te/MgxCd1−xTe (x > 0.13) double heterostructure (DH) solar cells with varying Mg compositions in the barrier layers are grown by molecular beam epitaxy. A Mg0.13Cd0.87Te/Mg0.37Cd0.63Te DH solar cell featuring abrupt interfaces between barriers and absorber and the addition of a SiO2 anti-reflective coating demonstrate open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), and device active-area efficiencies up to 1.129 V, 17.3 mA/cm2, 77.7%, and 15.2%, respectively. The VOC and FF vary oppositely with the MgxCd1−xTe barrier height, indicating an optimal design of the MgCdTe DHs as a trade-off between carrier confinement and carrier transport. Temperature-dependent VOC measurements reveal that the majority of carrier recombination in the devices occurs outside the DHs, in the a-Si:H hole-contact layer, and at the interface between the a-Si:H layer and the MgxCd1−xTe top barrier at room temperature. Simulation results for the device with the highest efficiency show that the p-type a-Si:H layer and the Mg0.37Cd0.63Te top barrier contribute 1.3 and 2.4 mA/cm2 JSC loss, respectively.

Loss Analysis of Monocrystalline CdTe Solar Cells With 20% Active-Area Efficiency

We report a monocrystalline CdTe/MgCdTe double-heterostructure solar cell with an a-Si:H hole contact and an ITO/SiO x electrode stack. Similar designs have achieved high open-circuit voltages, but low short-circuit current densities and fill factors have limited the cell efficiencies. We investigate the origin of these losses, and, in addressing some of them, achieve a maximum total-area efficiency of 18.5% and active-area efficiency of 20.3% measured under AM1.5G illumination. Additional cells have been measured with open-circuit voltages of up to 1.11 V, while still maintaining respectable fill factors and no rollover. The lack of rollover, either before or after open circuit, confirms the potential of this approach to reach very high efficiencies. The optical losses within the device are quantified and analyzed across the spectrum to determine if there exists potential for increased current generation through a reduction in parasitic absorption. In addition, fitting the current–voltage characteristic reveals that the leading cause of the less-than-ideal fill factor is series resistance, which contributes a 7% absolute loss.

Monocrystalline CdTe/MgCdTe Double-Heterostructure Solar Cells With ZnTe Hole Contacts

Monocrystalline p-ZnTe/i-MgCdTe/n-CdTe/n-MgC-dTe double-heterostructure solar cells are grown through a combination of molecular beam epitaxy (MBE) and metal–organic chemical vapor deposition (MOCVD) deposition techniques using two different dopants within the ZnTe contact layer. The recombination at the ZnTe/CdTe heterointerface is believed to be suppressed by the use of a double heterostructure with an intrinsic MgCdTe passivation layer. A comparison of the steady-state photoluminescence intensity of these cells with record- $V_{{\rm{oc}}}$ monocrystalline CdTe solar cells indicates the performance potential of devices with ZnTe contacts, while increases in the internal quantum efficiency demonstrate the benefit of using ZnTe over these previously demonstrated contacts. Solar cells utilizing a copper-doped ZnTe hole contact show promise in terms of built-in voltage but do not realize that potential in terms of $V_{{\rm{oc}}}$ with a power conversion efficiency of 9.4% and a $V_{{\rm{oc}}}$ of 819 mV. Solar cells utilizing an arsenic-doped ZnTe hole contact exhibit the highest power conversion efficiency, reaching 14.08% with an open-circuit voltage of 867 mV.

Post-annealing Effects on Characteristics of Crystalline Germanium Solar Cells with the Double Heterostructure

We fabricated crystalline germanium (c-Ge) heterojunction solar cells with a double heterostructure (DH) which consists of hydrogenated amorphous silicon (a-Si:H) layers. In the a-Si:H/c-Ge DH solar cell, the improvement of the conversion efficiency is obtained compared to the c-Ge solar cell having single heterostructure. We investigated effects of post-annealing on characteristics of Ge heterojunction solar cells. The open-circuit voltage (VOC) of Ge heterojunction solar cells increases with increasing post-annealing temperatures above 150 °C. The increase of VOC by post-annealing could be mainly explained by the improvement of passivation quality of a-Si:H for the c-Ge surface. Our results suggest that the a-Si:H double heterostructure is beneficial not only for c-Si-based heterojunction solar cells but also for c-Ge-based heterojunction solar cells.

Crystalline Si Heterojunction Solar Cells with the Double Heterostructure of Hydrogenated Amorphous Silicon Oxide

Hydrogenated amorphous silicon oxide (a-SiO:H) layers have been applied to fabricate crystalline silicon (c-Si) heterojunction solar cells. The a-SiO:H/c-Si double heterostructure (DH) solar cell shows a notable increase in short-circuit current, compared with the single heterostructure solar cell, owing to suppression of carrier recombination at the solar-cell back surface. Nevertheless, the characteristics of the DH solar cells are found to deteriorate sharply with decreasing c-Si substrate thickness, and the solar cell efficiency decreases from 17.5% (300 µm) to 12.1% (54 µm). In this article, the effect of c-Si substrate thickness on the performance of DH solar cells is discussed.