Implementation of full-area-deposited electron-selective TiOx layers into silicon solar cells

Abstract

We examine two different silicon solar cell designs featuring full-area electron-selective contacts based on ultrathin (2–3 nm) titanium oxide (TiOx) films deposited by atomic layer deposition. The first cell design applies a layer stack to the cell front, which is composed of an ultrathin intrinsic amorphous silicon (i-a-Si:H) layer for interface passivation, the TiOx film and an indium tin oxide (ITO) layer to provide a good lateral conductance for electrons to the metal fingers. Whereas carrier lifetime measurements on test structures promise high implied open-circuit voltages Voc up to 726 mV, the realized solar cells achieve disappointingly low Voc values <400 mV. The J-V parameters of this cell type are negatively affected by a reverse diode occurring due to the contacting of the TiOx by the high-work function ITO layer. In the second cell type, we implement a layer stack to the cell rear, which is composed of an ultrathin silicon oxide (SiOy) layer, the TiOx film and a full-area-deposited aluminum (Al) layer. Initial Voc values of these cells are relatively low (<600 mV), but improve significantly after annealing at 350°C. The best cell featuring a SiOy/TiOx/Al rear contact achieves an open-circuit voltage of 661 mV and an efficiency of 20.3%. No reverse diode is observed, which is attributed to the lower work function of the Al compared to ITO in the first cell design. From internal quantum efficiency measurements, we extract a rear surface recombination velocity Srear of (52±20) cm/s for our best cell, which is well compatible with efficiencies exceeding 23%.

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 .…”

Selectivity of TiOx‐Based Electron‐Selective Contacts on n‐Type Crystalline Silicon and Solar Cell Efficiency Potential

“…[7] The best silicon solar cells featuring an electron-selective contact based on TiO x have been achieved so far with TiO x layers deposited by thermal atomic layer deposition (ALD), covered by aluminum (Al). [4,[8][9][10] In 2016, an efficiency of 21.6% was demonstrated by Yang et al on a c-Si solar cell featuring a full-area SiO y /TiO x /Al rear contact. [4] Featuring a full-area rear metallization by thermal evaporation of a few nanometer thin Al and a 2 μm-thick Ag layer on the ALD-TiO x , this solar cell demonstrated the promising potential of ALD-TiO x as electron-selective layer on c-Si solar cells.…”

Twenty Percent Efficiency Crystalline Silicon Solar Cells with Solution-Processed Electron-Selective Contacts

“…It is really a challenging task to provide effective ESCs with low contact resistivity and excellent surface passivation simultaneously, especially for lightly doped n-type c-Si substrates . Numerous materials, for example, metal oxides, − nitrides, , and fluorides, − have been successfully verified to form ESCs with an n-type c-Si.…”