A extremely transparent passivating call (TPC) together front call for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, wonderful surface passivation and also high optical transparency. However, the simultaneously optimization that these attributes remains challenging. Here, we current a TPC consists of a silicon-oxide tunnel layer adhered to by 2 layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposit at various temperatures and a sputtered indium tin oxide (ITO) class (c-Si(n)/SiO2/nc-SiC:H(n)/ITO). If the vast band void of nc-SiC:H(n) guarantee high optical transparency, the double layer design enables good passivation and also high conductivity translating right into an boosted short-circuit present density (40.87 mA cm−2), fill factor (80.9%) and also efficiency of 23.99 ± 0.29% (certified). Additionally, this contact stays clear of the require for extr hydrogenation or high-temperature postdeposition annealing steps. Us investigate the passivation mechanism and also working principle of the TPC and carry out a loss analysis based on number simulations outlining pathways towards conversion efficiencies of 26%.
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At present, the performance of many crystalline silicon (c-Si) solar cells is limited by recombination in the diffused emitter regions and also at the contact between metal electrodes and the silicon absorber1. Maker designs that stop diffused emitter regions and also direct metal-absorber contacts, commonly denoted as passivated contacts, are an essential enablers for a more increase that efficiency. Therefore far, three principles have been developed that allow junction formation in crystalline silicon solar cell without diffused emitters. These concepts are: the silicon heterojunction (SHJ) based upon intrinsic and doped amorphous silicon2,3,4; the so-called TOPCon or POLO concepts using a combination of silicon oxide and also polycrystalline silicon (SiO2/poly-Si)5,6 and also the usage of steel oxides/nitrides/fluorides such together MoOx (refs. 7,8,9), TiN10 or LiF8.
While these approaches enable high efficiencies, castle come v a substantial drawback. The implementation of, for example, MoOx linked with intrinsic hydrogenated amorphous silicon (a-Si:H) permitted solar cells with an efficiency >23.5% (ref. 11). The short-circuit current density (Jsc) limited the efficiency due to the high amount of helminth absorption by the intrinsic a-Si:H layer. The other two principles have achieved efficiencies in the >25% range so far. However, as result of the low tape gaps and an extensive absorption coefficients of a-Si:H and also poly-Si (Fig. 1a), these layers reason stronger parasitic absorption casualty when contrasted to other nanocrystalline silicon/silicon alloys with comparable thickness however a higher band gap. In the instance of poly-Si, this optical losses space so major that the application of this call is up to now minimal to the behind side of c-Si solar cells12. The can also be plainly seen in Fig. 1a the for photon energies above 1.75 eV, nc-SiC:H(n) attributes the lowest absorption coefficient and also thereby the best transparency amongst these materials.
a, The in-house measured absorption coefficient of nc-SiC:H(n), nc-Si:H(n), nc-SiOx:H(n), a-Si:H(n) and poly-Si(n) provided in present passivating contacts. A reference absorption coefficient the c-Si is included53. The nanocrystalline silicon/silicon alloys exhibit pronounced free-carrier absorption at short photon energies because of the high doping density. b, map out of a silicon solar cell utilizing an n-type wafer through a TPC on former side making use of our arisen nc-SiC:H(n)/SiO2 stack. Considering the high paper resistance (approximately 106 Ω sq−1) that the nc-SiC:H(n), an additional ITO layer through a paper resistance of roughly 200 Ω sq−1 is provided for lateral transport. The back side consists of intrinsic and p-type hydrogenated amorphous silicon (a-Si:H(i/p)) and an ITO layer.
While nc-SiC:H(n) is an noticeable candidate to attain highly transparent former contacts, so far efficiencies have lagged behind due to difficulties in obtaining nc-SiC:H(n) that functions high transparency, an excellent conductivity and at the same time provides sufficient hydrogenation because that passivation. These three properties space the obstacles to be overcome for high efficiency c-Si solar cells, as shown in Supplementary keep in mind 1 in the Supplementary Information.
The present file demonstrates how to get over this limit by using specifically low-temperature processes and by the implementation of a highly transparent passivating call (TPC) plan consisting the a thin, wet-chemically get an impressive SiO2 tunnel oxide and also a hot-wire chemical vapour deposition (HWCVD) fabricated large band gap nc-SiC:H(n) (Eg of roughly 2.7–3 eV)13 contact layer, as portrayed in Fig. 1b. Here, we show an separately confirmed effectiveness of 23.99 ± 0.29%. This effectiveness was accomplished by introducing a twin layer ridge of nc-SiC:H(n) deposited very first with low and subsequently through high filament temperature to tackle the trade-off between passivation and conductivity. Furthermore, a methodical investigation and also optimization of the ITO sputtering conditions linked with a low-temperature curing contributed to the performance improvement.
For nc-SiC:H(n) deposit at short filament temperature (Tf −10 S cm−1 compared to filament temperatures in between 1,900 and also 2,100 °C wherein the electric conductivity drastically increases come 0.07–0.9 S cm−1 (see Supplementary note 2 for an ext information around the electric properties that nc-SiC:H(n)). Given that the greater band gap of nc-SiC:H(n) is a natural advantage in terms of optical transparency, the optimization of the nc-SiC:H(n) great still has to tackle the trade-off in between passivation and also conductivity the hampered earlier attempts to make reliable silicon solar cells with SiC-based contacts13,14.
Figure 2 mirrors the include open-circuit voltage (iVoc) of the c-Si(n) wafer symmetrically passivated by the TPC (Fig. 2a) and the call resistivity of the TPC ridge (Fig. 2b) together a function of the filament temperature. For a single nc-SiC:H(n) class (thickness that 30 nm) deposited at boosted filament temperature the passivation quality of the TPC is reduced, while high Tf is needed for low call resistivities (Fig. 2b). Thus, a single nc-SiC:H(n) layer deposit by HWCVD cannot maximize passivation quality and also minimize resistive losses at the same time. To overcome this trade-off, the filament temperature during the deposition was changed, for this reason a twin layer stack of nc-SiC:H(n) was implemented (9 nm for the first layer and 25–30 nm for the 2nd layer). The modified procedure starts v a lower Tf the 1,775 °C for the great in direct call with the tunnel oxide. This is followed by a class deposited making use of a higher Tf, i beg your pardon was initially varied as displayed in Fig. 2a. This dual layer nc-SiC:H(n) stack permits to save the passivation quality practically independent of Tf in the second stage resulting in a maximum iVoc that 740 mV. In ~ the same time, the call resistivity is preserved at a low worth of 38 mΩ cm2, as shown in Fig. 2b. Afford the very same low call resistivity in a solitary layer would reason a substantial loss in passivation quality (iVoc Fig. 2: Selectivity of the TPC.
Fig. 3: Passivation mechanism and also working principle of the TPC.
Fig. 4: Illustration of the development of TPC solar cells.
Fig. 5: Optical loss analysis of the optimized TPC solar cell.
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Fig. 6: Fill element loss analysis of the optimized TPC solar cell.