Double-Sided Passivated Contacts for Solar Cell Applications: An Industrially Viable Approach Toward 24% Efficient Large Area Silicon Solar Cells

Abstract

Tunnel layer passivated contacts have been successfully demonstrated for next-generation silicon solar cell concepts, achieving improved device performance stemming from the significantly reduced contact recombination of the solar cell contacts. However, these carrier-selective passivated contacts are currently deployed only at the rear side of the silicon solar cell, while the front side adopts a conventional diffused junction and contacting scheme. In this work, we report on the novelty and feasibility of deploying tunnel layer passivated contacts on both sides of a silicon wafer-based solar cell, featuring a textured front surface and a planar rear surface. In particular, we demonstrate that silicon solar cells incorporating our in-house developed electron-selective thermal-SiO x /poly-Si(n +) and hole-selective thermal-SiO x /poly-Si(p +) passivated contacts have a solar cell efficiency potential approaching 24%. Deploying contact passivation only at the rear side of the solar cell, we have reached a solar cell efficiency of 21.7%, using conventional screen printing for metallization. We present a systematic approach of evaluating our in-house developed electron-selective and hole-selective passivated contacts on both textured and planar lifetime test structures, as well as dark I-V test structures, to extract the recombination current density j 0 and the contact resistance R c of the passivated contact, which is used for process optimization as well as for subsequent efficiency potential prediction. The two key challenges aiming at a double-sided integration of passivated contacts are (1) parasitic absorption within the front-side highly doped poly-Si capping layer, requiring the processing of ultrathin (≤10-nm) contact passivation layers. This has been quantified by numerical simulation (using SunSolve™) and also solved experimentally, i.e., processing ultrathin 3-/10-nm hole/electron extracting SiO x /poly-Si(p + /n +) passivated contact layers, reaching an implied open-circuit voltage of 690/703 mV on a planar/textured silicon surface, which will even further enhance after SiN x capping. (2) Ensuring process compatibility with conventional screen printing: Screen printing on electron extracting poly-Si(n +) seems feasible; however, screen printing on holeextracting poly-Si(p +) is still a challenge. Solar cell precursors have been processed, showing excellent pre-metallization results (implied-V OC $ 713 mV). According to 1 our efficiency potential prediction (using the measured j 0 and R c values of our developed contact passivation layers), bifacial double-sided passivated contact solar cells (efficiency potential of $23.2%, using our layers) can clearly outperform rearside-only passivated contact solar cells (efficiency potential of $22.5%).

Investigation of H2 Plasma Incorporated ALD-TiOx Films as Hole-Selective Passivating Contacts in Crystalline Silicon Solar Cells

“…This fact was also highlighted by Mitra et al through simulations, indicating that as J 0e increases from 2 to 25 fA/cm 2 , its contribution to V oc increases from 18% to 80%. However, applying a poly-Si-based heterojunction on the front side can induce significant optical losses due to parasitic absorption . As a result, to further improve the efficiency of TOPCon cells and reduce manufacturing costs, it is essential to implement a carrier-selective, passivating contact that is transparent while providing good passivation quality and carrier selectivity on the front side.…”

Pulsed Laser Annealed Ga HyperdopedPoly‐Si/SiOxPassivating Contacts for High‐Efficiency Monocrystalline Si Solar Cells

“…It is, however, of interest to apply the passivating contacts on both sides of the cells to further improve the overall passivation, since the recombination on the front boron‐diffused surface is responsible for the largest power loss in TOPCon cells. [ 16–18 ]…”

“…It is, however, of interest to apply the passivating contacts on both sides of the cells to further improve the overall passivation, since the recombination on the front boron-diffused surface is responsible for the largest power loss in TOPCon cells. [16][17][18] Phosphorus-doped poly-Si/SiO x contacts show a very high implied open-circuit voltage (iV oc ) of >730 mV, with a very low dark saturation current density (J 0 ) below 1 fA cm −2 . [19][20][21] Conversely, borondoped (B-doped) poly-Si contacts have a lower iV oc of ∼710 mV with a J 0 value of ∼10 fA cm −2 .…”

Boron‐doped polysilicon using spin‐on doping for high‐efficiency both‐side passivating contact silicon solar cells

“…11,14,15 These results demonstrate the excellent passivation quality of passivating contacts using tunnel oxide and doped poly-Si structures. Owing to the more sensitive diffusion conditions of boron, fewer studies on p + poly-Si layers have been conducted [16][17][18][19][20][21][22][23][24][25][26][27][28] compared with n + poly-Si. This also results from the difficulty in doping silicon with boron because of the lower effective diffusivity and surface doping concentration of B in Si compared to that of P under the same annealing conditions.…”