Ultra‐Thin Poly‐Si Layers: Passivation Quality, Utilization of Charge Carriers Generated in the Poly‐Si and Application on Screen‐Printed Double‐Side Contacted Polycrystalline Si on Oxide Cells

Abstract

Herein, the various measures to improve the efficiency of large‐area screen‐printed double‐side contacted polycrystalline Si on oxide (POLO)‐cells are experimentally demonstrated. The short‐circuit current density Jsc increases by 0.6 mA cm−2 upon reducing the thickness of poly‐Si from 25 to 10 nm due to the reduction of the parasitic absorption in the poly‐Si layer at the textured front side of the cell. Additionally, it is shown for the first time that the minority carriers generated by light absorbed in the poly‐Si layer can at least partially be transferred into the crystalline Si base. Remarkably high implied open‐circuit voltage Voc,impl values are achieved with n‐type cell precursors by introducing an hydrogenation step by AlxOy after reducing the poly‐Si thickness, and by an additional annealing step after sputtering of transparent conductive oxides (TCOs). All cell precursors show Voc,impl values of up to 740 mV independent of the poly‐Si thickness. A reduction in the open‐circuit voltage Voc is observed during back‐end processing to 728 mV as measured on the final cells. A certified cell energy conversion efficiency of 22.3% is reported.

Polysilicon passivated junctions: The next technology for silicon solar cells?

“…First, photons absorbed in poly-Si are lost to recombination (although a recent study suggests a small percentage of minority carriers generated in the poly-Si might be collected). 109 Doped poly-Si has an absorption coefficient similar to that of c-Si, and the loss in J sc caused by such ''parasitic absorption'' has been quantified as 0.4-0.5 mA/cm 2 per 10 nm of poly-Si, when placed at the front of the solar cell, 110,111 as depicted in the top x axis of Figure 5. In addition, the The upper points and trend lines correspond to layers that have been metallized by screen printing.…”

Recent advancements in poly-Si/SiOxpassivating contacts for high-efficiency silicon solar cells: technology review and perspectives

“…To begin with, photons that have been absorbed by poly-Si are recombined (a tiny fraction of minority carriers produced in poly-Si may be gathered). 110 The absorption coef-cient of doped poly-Si is comparable to c-Si, and J SC loss due to this parasitic absorption was estimated to be $0.45 mA cm À2 for every 10 nm of poly-Si when put on the front side. 111,112 Furthermore, free charge carriers in the poly-Si layer absorb infrared photons in a similar fashion to those in c-Si.…”

Key Aspects of p-Type TOPCon on Textured Surface for Silicon Bottom Cells in Tandem Devices

“…For an excellent infrared response, a textured surface at the rear is indispensable. However, the realization of p-type TOPCon on textured surface morphology is particularly challenging due to a higher interface state density Dit -and thus recombination current density J0 [2] -as well as a decreased SiOx growth rate on (111)compared to (100)-oriented surfaces found on the pyramids' planes resulting in a nonuniformity in oxide growth across the wafer surface [3]. The latter is more relevant for p-type compared to n-type TOPCon as Boron (B) readily passes the poly-Si/ SiOx interface [4] and penetrates the oxide [5].…”