The interesting goal of heterojunction solar cell is to attain high module efficiency (>15 %) with “thin” silicon substrates (approximately 150 µm contrary to the average 300 µm in the current photovoltaic industry) or ribbons. This will highly decrease the price of solar modules. The prerequisite for such a challenge is a very good passivation of the crystalline (or multi-crystalline) silicon surface. This patent enables to improve passivation by engineering the band diagram of heterojunction solar cells. This patent enables to lower the thermal budget of solar cells’ fabrication by decreasing the temperature of the process.