A Method for Calculating Operating Characteristics of Silicon Heterojunction Solar Cells with Arbitrary Parameters of Cr
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od for Calculating Operating Characteristics of Silicon Heterojunction Solar Cells with Arbitrary Parameters of Crystalline Substrates I. E. Panaiottia*, E. I. Terukovb,c, and I. S. Shakhraib,d a Ioffe
Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia St. Petersburg State Electrotechnical University “LETI,” St. Petersburg, 197376 Russia c Research and Development Center for Thin-Film Technologies in Energetics, Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia d Hevel Group, Moscow, 117342 Russia *e-mail: [email protected] b
Received May 15, 2020; revised May 15, 2020; accepted May 19, 2020
Abstract—Specific features of the current processes in silicon heterojunction with intrinsic thin layer solar cells have been investigated. The proposed model takes into account the ambipolar motion of carriers and allows one to calculate the operating characteristics at an arbitrary ratio of the diffusion length and the crystalline-substrate thickness. A numerical method for estimating the recombination-loss rate on silicon wafer surfaces based on the comparative analysis of the experimental values of short-circuit current and open-circuit voltage is described. Keywords: heterojunction solar cells, crystalline silicon substrates, surface recombination loss. DOI: 10.1134/S1063785020090072
Heterojunctions with intrinsic thin layer (HIT) solar cells based on crystalline silicon are widely applied in modern solar arrays. To date, the efficiency of the best samples exceeds 26% [1, 2]. A further improvement of the operating characteristics of HIT cells is an urgent problem of modern solar power engineering. The process of HIT cell fabrication includes the formation of heterojunctions on both surfaces of a crystalline silicon (c-Si) substrate by depositing amorphous hydrogenated p- and n-silicon thin films. One generally uses c-Si wafers doped with donor impurity with concentration Nd ≥ 1015 cm–3 having initial freecarrier bulk lifetime τ0 ≥ 1.5 ms. The substrate is 90– 160 μm thick. A method for simulating processes in HIT cells with the use of experimental values of short-circuit current density Jsc was proposed in [3]. However, the developed theory took into account only the cases where Ldiff ≫ d (Ldiff is the carrier diffusion length and d is the substrate thickness). This relationship is not always valid under real conditions. For example, the carrier lifetimes in near-Earth orbits decrease radically due to irradiation of solar cells by high-energy particles and the diffusion length may be comparable to the substrate thickness. To interpret the experimental data
on a decrease in the Jsc values under irradiation of HIT cells, a model was proposed in [4], which is valid for an arbitrary relationship between the Ldiff and d values. However, only photoelectric-conversion conditions that are close to the short-circuit mode, when the concentration of excess carriers is small in comparison with the substrate doping level (Δp ≪ Nd), were consider
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