TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Method: In fabricating the back contact single hetero-junction solar cell, providing the first semiconductor substrate includes providing a substrate material selected from single crystalline silicon, multicrystalline silicon, polycrystalline silicon, amorphous silicon, single crystalline silicon-germanium, and III-V compound semiconductors. Forming the second semiconductor and third semiconductor layer includes forming each with a material selected from hydrogenated amorphous silicon, hydrogenated amorphous silicon carbide, hydrogenated amorphous silicon germanium, hydrogenated microcrystalline silicon oxide, microcrystalline silicon, III-V compound semiconductors, II-VI compound semiconductors, and organic semiconductors. The method further comprises: heavily doping a region of the substrate backside with the first dopant; where forming the second semiconductor includes depositing a second semiconductor in-situ doped with the second dopant; where forming the emitter includes forming the emitter in the second semiconductor; and where forming the base includes forming the base in the heavily doped region of the substrate backside. The method as well comprises: heavily doping a region of the substrate backside with the second dopant; where forming the second semiconductor includes depositing a second semiconductor in-situ doped with the first dopant; where forming the base includes forming the base in the second semiconductor; and where forming the emitter includes forming the emitter in the heavily doped region of the substrate backside. Forming the second semiconductor includes depositing a second semiconductor using a process selected from chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), hot wire chemical vapor deposition (HWCVD), high frequency plasma enhanced chemical vapor deposition (HFPECVD), high density plasma enhanced chemical vapor deposition (HDPECVD), inkjet printing, and screen printing. Moreover, the method comprises: selectively forming thermal oxide overlying the substrate backside; heavily doping regions of the substrate backside exposed through openings in the thermal oxide; forming a SiNx film overlying the substrate top surface and the heavily doped regions of the substrate backside; etching exposed regions of thermal oxide; depositing the second semiconductor through the etched openings in the thermal oxide overlying the substrate backside. Forming the third semiconductor layer includes forming the third semiconductor layer selected from depositing a third semiconductor layer, moderately doped with the first dopant, overlying the first semiconductor substrate topside, and doping the topside of the first semiconductor substrate. Providing the first semiconductor substrate lightly doped with the first dopant type includes providing an n-doped silicon substrate; and where forming the base in the substrate backside, heavily doped with the first dopant type, includes forming an n+ doped base in an amorphous silicon second semiconductor material. Preferred Solar Cell: In the solar cell, the first semiconductor substrate is material selected from single crystalline silicon, multicrystalline silicon, polycrystalline silicon, amorphous silicon, single crystalline silicon-germanium, and III-V compound semiconductors. The second semiconductor film and third semiconductor layer are each a material selected from hydrogenated amorphous silicon, hydrogenated amorphous silicon carbide, hydrogenated amorphous silicon germanium, hydrogenated microcrystalline silicon oxide, microcrystalline silicon, III-V compound semiconductors, II-VI compound semiconductors, and organic semiconductors. The substrate backside includes a region heavily doped with the first dopant; where the second semiconductor film is heavily doped with the second dopant; where the emitter is formed in the second semiconductor film; and where the base is formed in the heavily doped region of the substrate backside. The substrate backside includes a region heavily doped with the second dopant; where the second semiconductor film is heavily doped with the first dopant; where the base is formed in the second semiconductor; and where the emitter is formed in the heavily doped region of the substrate backside. The third semiconductor layer is selected from a separate semiconductor layer, moderately doped with the first dopant, deposited over the first semiconductor substrate topside, and a moderately doped region topside region of the first semiconductor substrate.