Bandgap engineered smart three‐terminal solar cell: New perspectives towards very high efficiencies in the silicon world

Abstract

We present the design of a new architecture of three-terminal (3-T) photovoltaic tandem solar cells. It combines an interdigitated back contacted (IBC) bottom lateral subcell with a heterojunction vertical top cell. In this concept, the two subcells can work independently and there is no need for tunnel junctions. It is particularly well suited to silicon back contact subcells and to various types of top cell materials from III-V compounds or perovskites. The working principle is detailed here using as an example a p/i III-V front stack onto n-type silicon IBC bottom cell. We perform two-dimensional (2D) modeling using realistic material input parameters and show how interface bandgap engineering can improve the tandem cell efficiency up to a reachable 35% value. The proposed cell concept named bandgap engineered smart silicon three-terminal (BESTT) cell can be realized with less technological steps and at a lower cost compared with the conventional four-terminal process.

Three-Terminal Perovskite/Silicon Tandem Solar Cells with Top and Interdigitated Rear Contacts

“…for the limiting case (which cannot be achieved in real world devices). At this point the two subcells become independent from each other, representing the ideal theoretical case as also discussed elsewhere [34]. Thus it can be concluded that during device fabrication utmost attention on designing this shared contact to be very lowly resistive as well as on choosing appropriate wafer material are crucial to minimize the mutual dependence of the subcells' J-V-characteristics.…”

“…In order to reach sufficient electron selectivity between the two subcells in a tandem device, the ETL adjacent to the perovskite must create an asymmetric energetic barrier [34] (see Figure 6a and b): The conduction band only experiences a small band offset, thus allowing electrons to pass [55] while holes are blocked by the considerable energetic barrier in the valence band. The simulated solar cell parameters for both subcells when set to MPP conditions in the IBC 3T configuration are included in Table S4.…”

“…Being a rather unconventional configuration, the number of published studies is fairly limited. Recently, several theoretical and experimental reports on the accurate operation of 3T devices and the expected interplay between the subcells have been published: a GaInP and Si cell wired in a quasi-3T configuration was experimentally and theoretically , reported, and more recently, a 3T IBC of individually fabricated GaInP and Si cells was realized by bonding the subcells with transparent conductive adhesive . Additionally, the influence of different top cell currents injected into an interdigitated back-contact (IBC) cell on its power output was experimentally evaluated, and it was found that the combined power output of the 3T tandem is independent of the amplitude of the top cell’s current .…”

Three‐terminal perovskite/integrated back contact silicon tandem solar cells under low light intensity conditions

“…This study considers a novel 3T device architecture, which features a carrier selective band offset barrier, [ 3 ] delivering 3T tandem efficiencies without the need for lateral transport layers, which contribute to parasitic absorption losses. In addition, the design eliminates the need for grid alignment to minimize shading that is a constraint in 4T designs.…”

“…[ 1 ] This study reports on the development of a novel device, the selective band offset three‐terminal tandem that presents advantages over existing designs, which has been experimentally demonstrated by two groups. [ 2,3 ]…”