Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25  device efficienc

Albrecht, S.

Becker, C.

Eisenhauer, D.

Jo t, M.

Jäger, K.

Köhnen, E.

Manley, P.

Sutter, J.

Tockhorn, P.

English

HZB Repository

Improving Monolithic Perovskite/Silicon TandemSolar Cells From an Optical ViewpointKlaus Ja¨ger,1,2,∗ Marko Josˇt,1 Johannes Sutter,1 Philipp Tockhorn,1 Eike Ko¨hnen,1David Eisenhauer,1 Phillip Manley,1,2 Steve Albrecht1 and Christiane Becker11 Helmholtz-Zentrum Berlin fu¨r Materialien und Energie, Hahn-Meitner Platz 1, 14019 Berlin, Germany2 Zuse Institute Berlin, Takustraße 7, 14195 Berlin, Germany* klaus.jaeger@helmholtz-berlin.deAbstract: Perovskite/silicon tandem solar cells are the most promising concept for a futurephotovoltaic technology. We report on recent progress from an optical viewpoint and disucsshow we achieved more than 25% device efficiency.OCIS codes: (350.6050) Solar energy; (040.5350) Photovoltaic; (000.4430) Numerical approximation and analysis;1. IntroductionCurrently, multi-junction solar cells are the only viable route to surpass the single-junction efficiency limit, which is29.4% for silicon [1]. Because of their excellent optoelectronic properties and the possibility to tune their bandgap,perovskites are the most promising material class to be combined with silicon in tandem solar cells. The first monolithicperovskite/silicon tandem cells, where the two subcells are electrically connected in series, were reported in 2015 with13.7% power conversion efficiency (PCE) [2]. Recently, 25.5% and 28% were reported on lab and industrial scale,respectively [3, 4]. The latter PCE exceeds the current single-junction record of 26.7% [5].In this contribution, we review the development of perovskite/silicon tandem solar cells in our research center. Afterpresenting optical simulations to assess the potential of these devices, we discuss the steps that were necessary to reach25.5% PCE. Finally, we discuss current efforts to texture the silicon wafers in order to reduce reflection losses.2. Optical simulationsOptical simulations are a valuable tool to study how varying the materials and thicknesses of the supporting layersaffects the optical performance of the solar cell. Further the effects of changing the perovskite material (and hencebandgap) and (nano)texturing can be investigated. Using the net-radiation method and a thickness optimization, wecould show that more than 30% PCE is theoretically achievable with a fully planar design for an optimal perovskitebandgap around 1.75 eV and a 250 µm thick silicon wafer [6]. A back-textured silicon wafer can further increase theshort circuit current density by about 1 mA/cm2 per subcell because of light trapping in silicon at long wavelengths [7].However, the reflection losses stay significant, because the front of the silicon bottom cell, the top cell and the frontinterface are planar. These reflective losses can be reduced significantly if the front side of the silicon wafer and theperovskite top cell are textured, as illustrated in Fig. 1(a). Figure 1(b) shows simulations results obtained with the finiteelement method: a sinusoidal nanotexture with 500 nm period and 500 nm amplitude could reduce the reflective lossesby ≈ 50% [8].3. Experimental realization of perovskite/silicon tandem solar cellsTo achieve 25.5% with a planar perovskite top cell, we used a light management (LM) foil, which was placed ontop of the tandem device and boosted the short circuit current density from 17.3 mA/cm2 to 18.5 mA/cm2, as shownin Figs. 1(c-e) [3]. The JV scans were performed in reverse direction. The LM foil carried the texture of a KOH-etched silicon wafer and was manufactured using UV-nanoimprint lithography. Further, we designed this cell in aninverted architecture with the electron-selective contact on top. This allowed us to reduce the parasitic absorptionlosses with respect to the regular design with Spiro-OMeTad as hole-selective front contact [6]. We used the multiplecation, multiple halide composition Cs0.05(MA0.17FA0.83)Pb1.1(I0.83Br0.17)3 as absorber material. The electron- andhole-selective contacts were C60 and the p-type polymer PTAA, respectively. As bottom cell we used a back-sidetextured and front-side polished rear emitter silicon-heterojunction cell.(b) (c)(e)(g)400 600 800 1000 1200wavelength (nm)0.00.20.40.60.81.0absorption, 1−Rperovskite21.3 mA/cm219.8 mA/cm2silicon21.3 mA/cm219.7 mA/cm2R2.85.5planar front17.3  mA/cm21.76 V76.4%23.4% LM foil18.5  mA/cm21.76 V78.5%25.5%JSCVOCFFPCE1 μmairNiOITOa-Si:H (n+)i a-Si:H (i)silicon (wafer)LiFITOSnO2PCBM(a)1 μmperovskitesiliconIZOSnO2C60a-Si:H (p)ZnO:AlAgPTAAITOnc-SiOx:Ha-Si:H (i)nc-SiOx:HperovskiteIZOsiliconLM foil(d)perovskitesol-gelglass 1 μm(f)Fig. 1. (a) Grid and (b) results of finite-element simulations of a nanotextured perovskite/siliconsolar cell [8]. (c) Scanning electron microscope (SEM) cross section, (d) sketch and (e) externalparameters of solar cells with and without light management (LM) foil [3]. SEM pictures of (f) spin-coated perovskite on a nanotextured substrate and (g) a sinusoidal nanotexture in silicon.4. Developing cells with nanotextured silicon/perovskite interfacesNanotextured silicon/perovskite interfaces can further improve light management. Smooth sinusoidal nanotextures arecompatible with spin-coating for perovskite deposition, as shown in Fig. 1(f) [8]. Before building complete tandemdevices, fabricating individual subcells with such nanotextures must be optimized. For the bottom cell, the texture istransferred into the silicon wafer by anisotropic reactive ion etching – a scanning electron microscope picture is shownin Fig. 1(g). An isotropic wet chemical etch of the Si wafer stripped off damaged silicon layers yielding minoritycarrier lifetimes of 700 µs at 1015 cm−3 minority carrier density, which is compatible with good device performance.For the perovskite top cell, we adjust the processing of the different layers to make it compatible with the nanotex-tured substrate. Proof-of-principle perovskite single-junction solar cells on sinusoidal nanotextures with peak-to-valleydimensions of up to 400 nm on glass substrates yield 16.5% stabilized PCE.5. OutlookOptical simulations and continuous material improvement allowed us to realize a monolithic perovskite/silicon tandemcell with 25.5% PCE. Currently, we are working on further improving the material quality of sinusoidally texturedsilicon wafers and hence on realizing tandem solar cells with nanotextured silicon-perovskite interfaces.References1. A. Richter, M. Hermle, and S. Glunz, “Reassessment of the limiting efficiency for crystalline silicon solar cells,” IEEE J. Photovolt. 3,1184–1191 (2013).2. J.P. Mailoa, C.D. Bailie, E.C. Johlin, E.T. Hoke, A.J. Akey, W.H. Nguyen, M.D. McGehee, and T. Buonassisi, “A 2-terminal per-ovskite/silicon multijunction solar cell enabled by a silicon tunnel junction,” Appl. Phys. Lett. 106, 121105 (2015)3. M. Josˇt, E. Ko¨hnen, A. B. Morales-Vilches, B. Lipovsˇek, K. Ja¨ger, B. Macco, A. Al-Ashouri, J. Krcˇ, L. Korte, B. Rech, R. Schlatmann,M. Topicˇ, B. Stannowski, and S. Albrecht, “Textured interfaces in monolithic perovskite/silicon tandem solar cells: advanced light man-agement for improved efficiency and energy yield,” Energy Environ. Sci. 11, 3511–3523 (2018).4. Oxford PV (2018). https://www.oxfordpv.com/news/oxford-pv-perovskite-solar-cell-achieves-28-efficiency.5. M. A. Green, Y. Hishikawa, E.D. Dunlop, D.H. Levi, J. Hohl-Ebinger, M. Yoshita and A.W.Y Ho-Baillie, “Solar cell efficiency tables(version 53),” Prog. Photovoltaics Res. Appl. 27, 3–12 (2019).6. K. Ja¨ger, L. Korte, B. Rech, and S. Albrecht, “Numerical optical optimization of monolithic planar perovskite/silicon tandem solar cellswith regular and inverted device architectures,” Opt. Express 25, A473–A482 (2017).7. K. Ja¨ger, M. Werth, L. Mazzarella, et al., “Numerical optical optimization of perovskite-silicon tandem solar cells,” in Proceedings of the33rd European Photovoltaic Solar Energy Conference and Exhibition, 1057–1060 (2017).8. D. Chen, P. Manley, P. Tockhorn, D. Eisenhauer, G. Ko¨ppel, M. Hammerschmidt, S. Burger, S. Albrecht, C. Becker, and K. Ja¨ger, “Nanopho-tonic light management for perovskite–silicon tandem solar cells,” J. Photonics Energy 8, 022601 (2018).

Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

Jäger, Klaus

Jošt, Marko

Sutter, Johannes

Tockhorn, Philipp

Köhnen, Eike

Eisenhauer, David

Manley, Phillip

Albrecht, Steve

Becker, Christiane

Publication Server of Zuse Institute Berlin (ZIB)

Improving Monolithic Perovskite/Silicon Tandem Solar Cells From an Optical Viewpoint

Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

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