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8th World Conference on Photovoltaic Energy Conversion; 83-87, Aluminium doped zinc oxide (AZO) is an interesting transparent conductive oxide (TCO) for silicon heterojunction (SHJ) solar cells to replace indium tin oxide (ITO) to enable cost reduction and omit the use of the limited global indium reserve. However, AZO layers have a much higher sheet resistance and lower damp heat stability compared to ITO. This work shows that the AZO stability can be improved by using an ITO capping layer, which is also decreasing the sheet resistance of the AZO/ITO layer stack compared to a pure AZO layer. Here, high rate rotatable magnetron sputtering was used to deposit AZO and ITO films. Under these conditions ITO capped AZO layers deposited on a-Si/p can result in lower fill factors. It will be shown that heating before sputtering and introduction of a thin ITO layer between AZO and a-Si/P avoid the fill factor decrease and lead to fill factors above 80%. The properties of the solar cells with the ITO/AZO/ITO layer stack are comparable to those solar cells with the pure ITO reference layer. Similar solar cell properties with the same ITO/AZO/ITO layer stack on the a-Si/n of the front side have been achieved. Furthermore, the TCO materials costs of ITO, AZO/ITO and ITO/AZO/ITO layers stacks for industrial manufacturing are discussed.

8th World Conference on Photovoltaic Energy Conversion; 202-207, In this work we report on the development of an industrially relevant in-situ doped sputtering process for depositing 100-150 nm thick aSi(n) layers to passivate the rear contact of TOPCon solar cells. All relevant properties of the poly-Si layers have been optimized using symmetrical lifetime samples. The sputtered aSi(n) layers do not show blistering effects and can be doped with Phosphorus concentrations larger than 1E21 at/cm³ which has been evaluated via calibrated SIMS measurements. ECV measurements of optimized layers after a high temperature anneal at 850-980 °C for 10-30 min confirm the necessary electrically active concentration cP ~ 1-3E20 at/cm³. After tuning the interfacial oxide layer and optimizing the PVD process parameters as well as the annealing process implied open circuit voltages iVoc > 735 mV could be measured on symmetrical lifetime structures at one sun injection density on 1-3 Ωcm n-type Cz-wafers. Corresponding sheet resistances of the 140 nm thick poly-Si layers range from 60-320 Ω/sq and sufficiently low specific contact resistivities below 10 mΩcm² for screen-printed contacts have been determined accompanied by low recombination of J0,met < 65 fA/cm². The best TOPCon solar cell with sputtered poly-Si layers has an efficiency of 23.4 % measured by ISE CalLab PV Cells.

35th European Photovoltaic Solar Energy Conference and Exhibition; 456-459, Sputtered indium tin oxide (ITO) is a widespread used material for application as transparent conducting oxide as the front contact of rear-junction silicon heterojunction solar cells. Standard ITO films suffer from too high parasitic absorption in both the short- and the long-wavelength range. The aim of this contribution is to investigate lower absorbing TCOs deposited with industrial DC sputtering from rotatable targets. High Voc values >735 mV demonstrate that in spite of the high-power industrial DC sputter process no significant sputter damage is observed, independent of the target material. Cell efficiencies up to 23.3% are obtained with titanium-doped (ITiO) and tin-doped indium oxide (ITO 99/1). The highest short circuit current values of 39.6 mA/cm2 are reached with an ultimately low-carrier and high-mobility indium-oxide-based material. The cell efficiency in this case, however, is over-compensated by a too low FF, mostly due to a higher contact resistivity and TCO sheet resistances. We ascribe this effect to the very low carrier concentration.