Two-step Photon Up-conversion Research Articles

Multi-step photon upconversion in quantum-dot-based solar cells with a double-heterointerface structure

Photon upconversion (PU) is a process where an electron is excited from the valence band to the conduction band of a wide-gap semiconductor by the sequential absorption of two or more photons via real states. For example, two-step PU can generate additional photocurrent in the so-called intermediate-band solar cells. In this work, we consider two- and three-step processes; we study multi-step PU in a quantum dot (QD)-based single-junction solar cell with a double-heterointerface structure. The solar cell consists of three different absorber layers: Al0.7Ga0.3As, Al0.3Ga0.7As, and GaAs, which form two heterointerfaces. Just beneath each heterointerface, an InAs/GaAs QD layer was inserted. After band-to-band excitation, electrons accumulate at each heterointerface, and then, below-bandgap photons excite a certain fraction of these electrons above the barrier energy. The photoluminescence spectra of the InAs QDs reveal slightly different QD size distributions at the two heterointerfaces. We show that the external quantum efficiency is improved by additional irradiation with below-bandgap infrared photons, which suggests a multi-step PU process that involves the two heterointerfaces. The dependence of the photocurrent on the infrared excitation power density only shows a superlinear behavior when the GaAs layer is excited but the Al0.3Ga0.7As layer is not. These data demonstrate a multi-step PU process that consists of one intraband transition at each of the two heterointerfaces and one interband transition in GaAs.

Numerical simulation on the impurity photovoltaic (IPV) effect in c-Si wafer-based dual-heterojunction solar cell

The impurity photovoltaic effect (IPV) with thallium (TI) impurity has theoretically been investigated in crystalline silicon (c-Si) wafer reigned dual-heterojunction (DH) solar cell that ensures an extended absorption of longer wavelength light with zinc selenide (ZnSe) window and aluminium antimonide (AlSb) back surface layers. The results imply that the incorporation of impurity enhances the photocurrent while the dual-heterojunction ensures the higher V OC of the proposed solar cell structure. The pristine Si (150 µm wafer) solar cell exhibits a power conversion efficiency (PCE) of 35.04% with J SC = 38.85 mA/cm 2 and V OC = 1.05 V, respectively. On the contrary, the introduction of Tl impurity within the bandgap of absorber enhances the PCE to 44.47%, with a J SC = 48.95 mA/cm 2 , V OC = 1.063 V and FF= 85.46%, respectively. This augmentations of the V OC and J SC and hence PCE is originated from the DH structure and longer wavelength light absorption due to impurity-assisted two-step photon upconversion phenomena in the solar cell. • IPV effect in an n + -p-p + Si DH solar cell with Tl impurity has been simulated. • ZnSe and AlSb have been used as window and BSF layers, respectively. • The optimized metal contacts Ti (cathode) and Ni (anode) has been established. • A maximum J SC of 48.95 mA/cm 2 and PCE= 44.47% with V OC = 1.063 V has been achieved. • n + - ZnSe /p- Si /p + - AlSb DH solar cell with Tl impurity shows potential in future.

Theoretical insight into the enhancement of longer-wavelength light absorption in silicon solar cell with multilevel impurities

In this article, we theoretically demonstrate multilevel impurity photovoltaic effect in an efficient silicon dual-homojunction solar cell that ensures an extended absorption of longer wavelength light. Along with suitable contact work functions (Ni and Ta as anode and cathode, respectively), three impurity energy levels from acceptor type impurities (One from Tl and two from Zn) have been introduced in the energy gap of the absorber layer of the solar cell. The simulations have been performed with Solar Cell Capacitance Simulator (SCAPS-1D) program. The pristine Si solar cell shows a PCE of 25.4% with JSC = 37.99 mA/cm2, VOC = 0.780 V and FF = 85.76%. While the incorporation of Tl impurity level alone provides a PCE of 33.4%, with JSC = 51.56 mA/cm2, VOC = 0.789 V and FF = 82.03%, respectively. The PCE of the solar cell further enhances to 35.4% with an elevation of the short circuit current by 3.76 mA/cm2 due to the inclusion of Zn impurity into the optimized structure. This increment of the JSC and hence PCE is evolved from the longer wavelength light absorption due to impurity-assisted two-step photon upconversion in the solar cell.

Theoretical insights into a high-efficiency Sb2Se3-based dual-heterojunction solar cell

Here, we manifest the design and simulation of an n-ZnSe/p-Sb2Se3/p+-AgInTe2 dual-heterojunction (DH) solar cell which exhibits a prominent efficiency. The performance of the solar cell has been assessed with reported experimental parameters using SCAPS-1D simulator by varying thickness, doping concentration and defect density in each layer. The proposed structure shows an efficiency of 38.6% with VOC = 0.860 V, JSC = 54.3 mA/cm2 and FF = 82.77%, respectively. Such a high efficiency close to Shockley-Queisser (SQ) limit of DH solar cell has been achieved as a result of the longer wavelength photon absorption in the p+-AgInTe2 back surface field (BSF) layer through a tail-states assisted (TSA) two-step photon upconversion phenomenon. These results indicate hopeful application of AgInTe2 as a bottom layer in Sb2Se3-based solar cell to enhance the cell performance in future.

Computational investigation on the photovoltaic performance of an efficient GeSe-based dual-heterojunction thin film solar cell

This article reports the design and computational analysis of an efficient GeSe-based n-ZnSe/p-GeSe/p +-WSe2 dual-heterojunction (DH) thin film solar cell using SCAPS-1D simulation program with physical parameters from the literature. The device has been optimized considering the thickness, doping and defect density of each layer. The optimized device shows an efficiency of ∼42.18% with a short circuit current density, J SC of 47.84 mA cm−2, an open circuit voltage, V OC of 1.07 V and fill factor, FF of 82.80%, respectively that remains within the Shockley-Queisser limit of a DH solar cell. The raised built-in potential developed between the two interfaces of the devices produces a surpassing V OC. The higher J SC is attributed to the current generated by absorption of sub-band gap photons by a tail-states-assisted two-step photon upconversion mechanism in the WSe2 back surface field layer. These results indicate the potential of manufacturing the high efficiency GeSe-based DH solar cell in future.

Simulating the performance of a high-efficiency SnS-based dual-heterojunction thin film solar cell

This article demonstrates a novel high efficiency ZnS/SnS/MoS2 dual-heterojunction thin film solar cell. The device has been optimized with respect to the thickness, doping concentration, and defect density of each constituent layer including working temperature and back contact metal work function using SCAPS-1D simulator. The MoS2 plays a promising role to serve as a back surface field (BSF) layer with commendatory band alignment, which provides an opportunity for higher absorption of longer wavelength photons utilizing the tail-states-assisted (TSA) two-step photon upconversion approach. The insertion of MoS2 in the ZnS/SnS pristine structure offers a significant improvement of the power conversion efficiency (PCE) within the detailed-balance limit with a rise from 20.1 to 41.4% with VOC of 0.91 V, JSC of 53.4 mA/cm2 and FF of 84.9%, respectively. This result reveals MoS2 as an effective BSF for low cost, highly efficient dual-heterojunction structure for future fabrication.

Voltage boost effects in two-step photon upconversion solar cells with a modulation-doped structure

A two-step photon upconversion (TPU) solar cell is a single-junction solar cell with a suitably designed heterointerface in the intrinsic layer. At this interface, upconversion can take place by absorbing infrared light, which excites carriers to energies above the heterojunction barrier, and then an electric field extracts these upconverted carriers to the barrier material. In this work, we study this photoabsorption process in a TPU solar cell with a modulation-doped structure. The modulation doping technique enables us to control the electric field at the heterointerface, and we demonstrate that the efficiency of the TPU process strongly depends on the electric field at the heterointerface. While we show that the TPU process induced by infrared light leads to a significant increase in the external quantum efficiency, we also note that this TPU process is an adiabatic process. It is shown that the adiabatic intraband photoexcitation at the heterointerface is able to increase the open-circuit voltage even above the open-circuit voltage that we predict from the diode equation and the actual current increase. We demonstrate obvious voltage boost effects and elucidate the relationship between the current and voltage.

Reciprocal Relation Between Intraband Carrier Generation and Interband Recombination at the Heterointerface of Two-Step Photon Up-Conversion Solar Cells

Photon up-conversion processes are considered beneficial for energy-conversion devices. The recently proposed two-step photon up-conversion (TPU) solar-cell design employs an intermediate level with a high electron occupation probability. To understand the device physics, a quantitative evaluation of the different current-generation and loss mechanisms is required. In the present work, we use a TPU solar cell containing an $\mathrm{In}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ quantum-dot layer located 10 nm in front of an ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ heterointerface. We study the relation between the photocurrent (PC), radiative recombination, and nonradiative recombination as a function of the bias voltage. The radiative interband recombination is evaluated by integrating the photoluminescence (PL) over the range from 1000 to 1300 nm. The magnitudes of the PC and PL signals generated via interband excitation of the $\mathrm{Ga}\mathrm{As}$ layer depend on the bias voltage; a higher forward bias reduces the PC and increases the PL intensity. We verify that, under additional infrared light illumination at 1319 nm, which induces intraband transitions, the PC density increases while the PL intensity significantly decreases. This PC enhancement exhibits a maximum at \ensuremath{-}0.6 V, which reflects the optimum internal electric field strength for maximizing the TPU efficiency.

Increasing conversion efficiency of two-step photon up-conversion solar cell with a voltage booster hetero-interface

Development of high-efficiency solar cells is one of the attractive challenges in renewable energy technologies. Photon up-conversion can reduce the transmission loss and is one of the promising concepts which improve conversion efficiency. Here we present an analysis of the conversion efficiency, which can be increased by up-conversion in a single-junction solar cell with a hetero-interface that boosts the output voltage. We confirm that an increase in the quasi-Fermi gap and substantial photocurrent generation result in a high conversion efficiency.

Two-step photon up-conversion solar cells

Reducing the transmission loss for below-gap photons is a straightforward way to break the limit of the energy-conversion efficiency of solar cells (SCs). The up-conversion of below-gap photons is very promising for generating additional photocurrent. Here we propose a two-step photon up-conversion SC with a hetero-interface comprising different bandgaps of Al0.3Ga0.7As and GaAs. The below-gap photons for Al0.3Ga0.7As excite GaAs and generate electrons at the hetero-interface. The accumulated electrons at the hetero-interface are pumped upwards into the Al0.3Ga0.7As barrier by below-gap photons for GaAs. Efficient two-step photon up-conversion is achieved by introducing InAs quantum dots at the hetero-interface. We observe not only a dramatic increase in the additional photocurrent, which exceeds the reported values by approximately two orders of magnitude, but also an increase in the photovoltage. These results suggest that the two-step photon up-conversion SC has a high potential for implementation in the next-generation high-efficiency SCs.