Study of interdigitated back contact silicon heterojunctions solar cells by two-dimensional numerical simulations

Silicon heterojunctions (SHJ) using thin layers of hydrogenated amorphous silicon (a-Si:H) deposited at low temperature on a crystalline silicon (c-Si) substrate are good candidates for high efficiency solar cells. In spite of achieving more than 22% efficiencies, the standard double HJ solar cells are limited by optical absorption and reflection at the front surface. Because it could help to overcome those limitations, the potential use of interdigitated back contact silicon heterojunctions (IBC–SHJ) structure for solar cells needs to be studied. To achieve realistic IBC–SHJ modelling, we use ATLAS 2-D device simulation software that allows accurate bulk and interface defects modelling. We here focus on IBC–SHJ structure on p-type c-Si simulations varying the values of the following parameters: bulk lifetime, surface recombination velocity at both front and back surfaces, bulk thickness, density of defects at the a-Si:H/c-Si interface. The influence of these parameters has been tested by generating the current–voltage (I–V) and spectral response curves. Results indicate that the key parameters to achieve high efficiency are a high crystalline substrate quality, low surface recombination velocity especially at the front surface, and a low recombining a-Si:H/c-Si interface. The simulations show that efficiencies up to 24% can be achieved with textured IBC–SHJ solar cells.