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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.

Crystalline silicon (c-Si) wafer-based solar cells have been dominating the current photovoltaic industries. However, prevalent manufacturing practices are based on environmentally-harmful chemicals and expensive methodologies. This paper reports on the development of inexpensive, environmentally-benign phosphoric acid-based emitter formation methods as an alternative to conventional highly toxic and poisonous POCl 3 gas source-based chemistry. Two emitter formation approaches at temperatures in 850-925 o C range have been investigated. The first approach is referred to as the doctor blade (DB) technique, where the flat Si wafer surface is uniformly coated by phosphoric acid (H 3 PO 4 ) via a moving blade. A small gap between the blade and wafer is maintained in order to form a thin uniform film on the wafer. The second method is referred to as the extension of the blade method (EDB), where an un-doped wafer is placed proximately to the deposited H 3 PO 4 wafer. During the high temperature drive-in process, phosphorous emitter was formed on the un-doped wafer surface through evaporation and deposition of phosphorus atoms from H 3 PO 4 coated wafer. All diffusion processes were carried out on 180 µm thick, planar boron-doped Si wafers in a conventional quartz tube furnace. The variation of sheet resistances over a broad range from ~20-180 Ω/sq were consistent with temperature dependence. Highest diffusion uniformity was observed for 10% H 3 PO 4 solution. Diffusion process simulations based on DifCad software were in good agreement with experimental data. The work reported here illustrates that an environmentally-benign approach in emitter formation based on H 3 PO 4 is feasible for manufacturing solar cells. ABSTRAKSel suria berasaskan wafer silikon hablur (c-Si) telah mendominasi industri fotovoltan masa kini. Walau bagaimanapun, amalan pengilangan lazim adalah berdasarkan penggunaan bahan kimia yang berbahaya dan kaedah yang mahal. Kertas kajian ini melaporkan tentang pembangunan kaedah pembentukan pemancar yang murah, mesra alam sekitar berasaskan asid fosforik sebagai alternatif kepada bahan bertoksik dan sumber gas kimia beracun konvensional berasaskan POCl 3 . Dua pendekatan pembentukan pemancar pada julat suhu o C dikaji. Pendekatan pertama merujuk kepada teknik bilah doktor (DB), di mana permukaan rata wafer Si disalut secara seragam oleh asid fosforik (H 3 PO 4 ) melalui bilah bergerak. Jurang kecil diantara bilah dan wafer dikekalkan bagi membentuk satu filem nipis seragam di atas wafer. Kaedah kedua merujuk kepada teknik bilah doktor lanjutan (EDB) dimana wafer tidak terdop diletakkan berhampiran dengan wafer yang telah dimendapkan dengan filem H 3 PO 4 . Semasa proses pandu masuk bersuhu tinggi, pemancar fosforus terbentuk di atas permukaan wafer tidak terdop melalui penyejatan dan pemendapan atom fosforus dari wafer bersalut H 3 PO 4 . Semua proses peresapan dijalankan ke atas wafer silikon terdop boron berstruktur satah dengan ketebalan 180 µm di dalam relau tiub kuarza konvensional. Variasi rintan...

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