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Low temperature processing of crystalline Si solar cells is attractive due to lower wafer and manufacturing costs. For thinner silicon wafers, thermal mismatch between Al and Si at high temperatures leads to thermal stress and wafer bowing. In this paper, replacement of back surface Al BSF contact by ITO films has been investigated as a function of Al-doping level. ITO films were deposited on back Si surfaces with sheet resistances in ∼16-48Ω/, range. ITO/Si contact resistance increases slightly as sheet resistance is reduced, however, the variation is not significant. At sheet resistance of 25Ω/,, solar cell performance comparable to conventional AL BSF configuration. Even at sheet resistance ∼50Ω/,, it is possible to form high quality ITO/Si contact. The role of surface defects has been deemed to be critical. Without etching of Al-doped surface, surface quality is poor due to defects originating from the Al-alloy formation. As these defects are removed with controlled etching, a more pristine surface emerges that forms superior contacts with ITO film.

Pulsed laser sources are attractive on account of their spatial and temporal controllability at room temperature. Pulsed lasers, in visible (VIS) (300 -515 nm) and infrared (IR) (900 -1064 nm) spectral ranges, with pulse widths in micro to femtoseconds range, are used in a wide range of applications including doping, etching, texturing and deposition. In this study, an Nd-YAG dicing laser operating at 1064 nm wavelength with 200 nanosecond pulse duration has been employed to form silver ohmic contacts to an n-type emitter on a p-type silicon substrate. The laser beam was used to anneal screenprinted Ag polymer paste over a broad (~ 7 to 500 mJ/cm 2 ) range of laser fluences. Computer numerical control software allowed fabrication of geometrical patterns with controllable diameters in 50-150-µm range. Contact resistance measurements were performed using the transmission line method (TLM). Contact resistivity exhibited fast decay from very large values to relatively constant as a function of laser fluence. This variation was attributed to laser energy below the threshold energy which no alloyed Ag/Si contact could be formed. The lowest contact resistivity at 200 mΩ.cm 2 was measured at 35 mJ/cm 2 . This value was two orders of magnitude higher than the lowest value for thermally annealed contacts. For the laser parameters investigated here, optimum laser fluences were in 0.2-0.6 J/cm 2 range. It may be possible to attain lower resistivity values trough post-laser annealing. ABSTRAK Sumber laser denyut mempunyai kelebihan kerana keboleh-kawalan ruang dan masa pada suhu bilik. Laser denyut, dalam julat spektrum nampak (VIS) (300-515 nm) dan inframerah (IR) (~900-1064 nm), dengan lebar denyutan dalam julat mikro hingga femtosaat, telah digunakan dalam pelbagai aplikasi termasuk pendopan, pemunaran, penteksturan dan pemendapan. Dalam kajian ini, pengguris laser Nd-YAG beroperasi pada panjang gelombang 1064 nm dengan tempoh denyutan 200 nanosaat telah digunakan untuk membentuk sentuhan ohmik perak pada pemancar jenis-n di atas substrat silikon jenis-p. Alur laser telah digunakan untuk menyepuh-lindapkan pes polimer perak yang dicetak skrin dengan meliputi julat kelancaran laser yang luas (~7 hingga 500 mJ/cm 2 ). Perisian kawalan numerik komputer pula membolehkan fabrikasi pola geometri dengan julat diameter boleh kawal dalam julat 50-150 μm. Pengukuran rintangan sentuhan telah dijalankan menggunakan kaedah garis penghantaran (TLM). Kerintangan sentuhan memperlihatkan susutan pantas dari nilai yang sangat besar kepada nilai malar secara relatif dengan fungsi kelancaran laser. Variasi ini disumbangkan oleh tenaga di bawah tenaga ambang laser yang tidak boleh membentuk hubungan Ag/Si aloi. Kerintangan sentuhan yang paling rendah pada nilai 200 mΩ.cm 2 telah diukur pada 35 mJ/cm 2 . Nilai ini adalah dua peringkat magnitud lebih tinggi daripada nilai terendah bagi sentuhan sepuh lindap terma. Bagi parameter laser yang digunakan dalam penyiasatan ini, kelancaran laser yang optimum berada dalam julat 0.2-0.6 J/cm 2 . Nila...

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