Fully screen‐printed silicon solar cells with local Al‐p⁺ and n‐type POLO interdigitated back contacts with a V_OC of 716 mV and an efficiency of 23%

Abstract

We demonstrate the fabrication of a fully screen‐printed p‐type silicon solar cell with local hole‐collecting Al‐alloyed (Al‐p+) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P‐diffused emitter by a passivating n‐type poly‐Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al‐p+ contacts are also located at the rear side to avoid front‐side shading. This results in a POLO‐IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm2 fabricated on a M2‐sized wafer. Scanning electron microscopy reveals an Al‐p+ thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al‐p+ contacts. A comparison of measured and simulated current‐voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al‐p+ contact of J0‐Al ‐p+ = 2,250 fA cm−2 for the current screen‐print conditions and Al‐paste causing an absolute efficiency loss of 0.5%abs. The recombination at the AlOx/SiNy surface and the shunt resistance limits the cell by 0.6%abs each.

Monolithic Perovskite/Silicon Tandem Solar Cells Fabricated Using Industrial p‐Type Polycrystalline Silicon on Oxide/Passivated Emitter and Rear Cell Silicon Bottom Cell Technology

“…They reached an even higher V OC of 716 mV after further optimization of the contact geometry. In a tandem cell, the photocurrent is roughly halved compared with the situation in the study by Haase et al [ 45 ] . Thus the optimum area fraction when balancing resistive and recombination losses should be even lower than in the single‐junction application.…”

“…Thus the optimum area fraction when balancing resistive and recombination losses should be even lower than in the single‐junction application. In tandem operation, the roughly halved photogeneration in the silicon subcell also reduces the bottom cell V OC contribution compared with the 1 sun situation in the study by Haase et al [ 45 ] . We thus expect that a bottom cell V OC contribution of 700 mV is feasible for our devices after optimizing the contact area fraction and the Al p + contact geometry.…”

“…Haase et al investigated the effect of the area fraction of local Al‐p + contacts formed in a similar process. [ 45 ] They identified the reduction of the Al‐p + contact area fraction as an efficient way to improve the V OC of p‐type silicon IBC cells with n + ‐POLO emitter and Al‐p + base contacts up to 709 mV at an area fraction of 1%. They reached an even higher V OC of 716 mV after further optimization of the contact geometry.…”

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

“…Different passivating contact schemes are currently evaluated for application in highly efficient silicon solar cells. Here, the advantage of polycrystalline silicon on oxide (POLO) junctions 1–4 and related junction schemes 5–8 as compared to other candidates like a‐Si:H/c‐Si heterojunctions, 9,10 transition metal oxides 11,12 or organic materials, 13 is their high level of thermal stability, which is derived from the high preparation temperature of POLO junctions. A high level of thermal stability implies potential compatibility with conventional mainstream high‐temperature screen‐print metallization 14 .…”

Sputtered Phosphorus‐Doped poly‐Si on Oxide Contacts for Screen‐Printed Si Solar Cells

“…This passivation and firing process were demonstrated to allow for efficient screen‐printed solar cells that have poly‐Si‐based passivating contacts. [ 40,41 ]…”