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Register a new userThe Effect of Hybrid Photovoltaic Thermal Device Operating Conditions on Intrinsic Layer Thickness Optimization of Hydrogenated Amorphous Silicon Solar Cells
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Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favourable operating temperatures for the thermal system. Amorphous silicon not only has a smaller temperature coefficient than c-Si, but also can display improved PV performance over extended periods of higher temperatures by annealing out defect states from the Staebler-Wronski effect. In order to determine the potential improvements in a-Si:H PV performance associated with increased thicknesses of the i-layers made possible by higher operating temperatures, a-Si:H PV cells were tested under 1 sun illumination (AM1.5) at temperatures of 25oC (STC), 50oC (representative PV operating conditions), and 90 oC (representative PVT operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840 nm were evaluated at each temperature. Results show that operating a-Si:H-based PV at 90 oC, with thicker i-layers than the cells currently used in commercial production, provided a greater power output compared to the thinner cells operating at either PV or PVT operating temperatures. These results indicate that incorporating a-Si:H as the absorber material in a PVT system can improve the thermal performance, while simultaneously improving the electrical performance of a-Si:H-based PV.
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There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance, however, this causes the thermal component to under-perform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be operated at higher temperatures and are a potential candidate for a more symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced degradation known as the Staebler-Wronski effect (SWE). Fortunately, SWE is reversible and the a-Si:H PV efficiency can be returned to its initial state if the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on the solar thermal absorber plate where the cells could reach the high temperatures required for annealing. In this study, this opportunity is explored experimentally. First a-Si:H PV cells were annealed for 1 hour at 100degreeC on a 12 hour cycle and for the remaining time the cells were degraded at 50degreeC in order to simulate stagnation of a PVT system for 1 hour once a day. It was found that, when comparing the cells after stabilization at normal 50degreeC degradation, this annealing sequence resulted in a 10.6% energy gain when compared to a cell that was only degraded at 50degreeC.
We report on very high enhancement of thin layers absorption through band-engineering of a photonic crystal structure. We realized amorphous silicon (aSi) photonic crystals, where slow light modes improve absorption efficiency. We show through simulation that an increase of the absorption by a factor of 1.5 is expected for a film of aSi. The proposal is then validated by an experimental demonstration, showing an important increase of the absorption of a layer of aSi over a spectral range of 0.32-0.76 microns.
The increase in the temperature of photovoltaic (PV) solar cells affects negatively their power conversion efficiency and decreases their lifetime. The negative effects are particularly pronounced in concentrator solar cells. Therefore, it is crucial to limit the PV cell temperature by effectively removing the excess heat. Conventional thermal phase change materials (PCMs) and thermal interface materials (TIMs) do not possess the thermal conductivity values sufficient for thermal management of the next generation of PV cells. In this paper, we report the results of investigation of the increased efficiency of PV cells with the use of graphene-enhanced TIMs. Graphene reveals the highest values of the intrinsic thermal conductivity. It was also shown that the thermal conductivity of composites can be increased via utilization of graphene fillers. We prepared TIMs with up to 6% of graphene designed specifically for PV cell application. The solar cells were tested using the solar simulation module. It was found that the drop in the output voltage of the solar panel under two-sun concentrated illumination can be reduced from 19% to 6% when graphene-enhanced TIMs are used. The proposed method can recover up to 75% of the power loss in solar cells.
Here we describe a new high frequency/high field continuous wave and pulsed electrically detected magnetic resonance (CW EDMR and pEDMR) setup, operating at 263 GHz and resonance fields between 0 and 12 T. Spin dependent transport in illuminated hydrogenated amorphous silicon p-i-n solar cells at 5 K and 90 K was studied by in operando 263 GHz CW and pEDMR alongside with complementary X-band CW EDMR. Benefiting from the superior resolution at 263 GHz, we were able to better resolve EDMR signals originating from spin dependent hopping and recombination processes. 5 K EDMR spectra were found to be dominated by conduction and valence band tale states involved in spin dependent hopping, with additional contributions from triplet exciton states. 90 K EDMR spectra could be assigned to spin pair recombination involving conduction band tail states and dangling bonds as dominating spin dependent transport process, with additional contributions from valence band tail and triplet exciton states.
In this study, the optoelectronic properties of a monolithically integrated series-connected tandem solar cell are simulated. Following the large success of hybrid organic-inorganic perovskites, which have recently demonstrated large efficiencies with low production costs, we examine the possibility of using the same perovskites as absorbers in a tandem solar cell. The cell consists in a methylammonium mixed bromide-iodide lead perovskite, CH3NH3PbI3(1-x)Br3x (0 < x < 1), top sub-cell and a single-crystalline silicon bottom sub-cell. A Si-based tunnel junction connects the two sub-cells. Numerical simulations are based on a one-dimensional numerical drift-diffusion model. It is shown that a top cell absorbing material with 20% of bromide and a thickness in the 300-400 nm range affords current matching with the silicon bottom cell. Good interconnection between single cells is ensured by standard n and p doping of the silicon at 5.10^19cm-3 in the tunnel junction. A maximum efficiency of 27% is predicted for the tandem cell, exceeding the efficiencies of stand-alone silicon (17.3%) and perovskite cells (17.9%) taken for our simulations, and more importantly, that of the record crystalline Si cells.
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