Reduction of absorption losses and efficiency gains by investigating amorphous/crystalline SHJ rear emitter solar cells
In this work, we discuss the results of a 2-dimensional numerical device simulation study concerning amorphous/crystalline silicon heterojunction (a-Si/c-Si SHJ) solar cells. In this context we address the fundamental challenge of balancing the trade-off between transparency and conductivity of transparent conducting oxides (TCO) at the illuminated front side of the solar cell. We investigate fill factor losses associated to the 2D lateral carrier transport, by varying the pitch of the front side metallization and the sheet resistance (Rsh) of the TCO for both, front emitter and rear emitter solar cells. It is demonstrated that for the rear emitter design a substantial part of the lateral carrier transport can be shifted from the front side TCO into the base. Due to this additional lateral current path, the trade-off between optical and electrical properties of the front side TCO is less pronounced for this rear emitter cells. This leads to fewer restrictions for the choice of the front side TCO and/or the design of the front side metallization. Depending on the optimization route, this should allow higher solar cell efficiencies or the application of more economically TCOs.