Minimizing Current and Voltage Losses to Reach 25% Efficient Monolithic Two-Terminal Perovskite–Silicon Tandem Solar Cells

Abstract

The rapid rise in efficiency and tunable bandgap of metal-halide perovskites makes them highly attractive for use in tandems on silicon. Recently we demonstrated a perovskite–silicon monolithic two-terminal tandem with 23.6% power conversion efficiency. Here, we present work on optical optimization to improve light harvesting that includes thinning out the top transparent electrode to reduce front-surface reflection and parasitic absorption; introducing metal fingers to minimize series resistance losses; and further minimizing reflection loss with a polydimethylsiloxane (PDMS) stamp with random, pyramidal texture. Additionally, to reduce voltage loss while achieving current matching, we employ poly­[bis­(4-phenyl)­(2,4,6-trimethylphenyl)­amine] (PTAA) as a hole transport material instead of NiO x and a wider 1.68 eV bandgap perovskite composition. These optimizations boost the open-circuit voltage to 1.77 V and the short-circuit current density to 18.4 mA/cm2, culminating in a 25% efficient perovskite–silicon tandem with a 1 cm2 active area.

Two‐Terminal Perovskites Tandem Solar Cells: Recent Advances and Perspectives

“…Apart from being a diffusion barrier, the ZTO layer was also necessary for achieving a low contact resistance with an ITO and a high fill factor. As a result, the two‐terminal tandem with 1 cm 2 active area reached a PCE of 23.6%, with negligible parasitic absorption and excellent stability for 1000 h. In 2018, the same group improved the two‐terminal tandem efficiency to 25.0%, by minimizing the reflection, managing the absorber bandgap and optimizing the device contact. To reduce the reflection, the front ITO electrode was thinned to 50–60 nm, which blue‐shifted the reflection maximum to 400 nm and simultaneously decreased the parasitic absorption.…”

“…There are several well‐identified routes to minimize a parasitic loss, and one strategy is reducing the layer thickness of transparent electrodes . By adjusting the thickness of front ITO layers from 150 to 60 nm, both the parasitic absorption and reflection were efficiently decreased. However, the optical simulation indicated that thicker ITO layers give rise to significant parasitic absorption, whereas thinner layers result in a reduced fill factor (FF) due to high series resistance .…”

“…The flat PDMS exhibits much lower reflectance (8.12%) than that of bare c‐Si (38%) at 550 nm, which can be further reduced for textured PDMS. Bush et al found that fabrication of a patterned PDMS scattering layer on the front surface of top‐cells could efficiently reduce reflection and thereby increase J SC . According to Hou et al, the J SC was improved by 1.72 mA cm −2 , and the perovskite–Si tandem efficiency was increased from 19.38% to 21.93%, after laminating the micro‐structured PDMS‐based ARC onto the front surface to boost light absorption (Figure b–e).…”

“…The improvement was ascribed to the reduced light reflection over short wavelength range. By combining the aforementioned strategies, the 1.68 eV FA 0.75 Cs 0.25 Pb(I 0.8 Br 0.2 ) 3 top‐cell yielded a 15.8% efficiency with a high J SC of 19.6 mA cm −2 . More recently, Jošt et al accomplished a 25.5% efficient monolithic tandem solar cell with an active area of 0.81 cm 2 , enabled by utilizing a rear‐side textured SHJ bottom‐cell while applying a textured LM foil at the front side of the top‐cell (Figure a).…”

“…Efficiency record evolution of two‐terminal perovskite–silicon, perovskite–perovskite, and perovskite–CIGS tandem devices, as well as four‐terminal perovskite–silicon, perovskite–perovskite and perovskite–CIGS tandems, according to the online publication date.…”