SrF_x‐based electron‐selective contact with high tolerance to thickness for crystalline silicon solar cells enabling efficiency over 21%

Abstract

Wide‐bandgap metal compound‐based dopant‐free passivating contacts have been explored to fabricate crystalline silicon (Si) solar cells to mitigate the high carrier recombination rate of metal‐Si contact directly. Here, an over 4‐nm‐thick single‐layer strontium fluoride (SrFx) and a double‐layer SrFx/lithium fluoride (LiF) films deposited by a facile vacuum thermal evaporation are developed to act as high‐performance electron‐selective contacts. SrFx with ultra‐low work function (2.8 eV) induces a strong downward band bending at the n‐type Si (n‐Si)/SrFx interface, and a dipole active layer exists at the SrFx/aluminum (Al) interface, enabling a low contact resistivity (ρc) of 34.1 mΩ cm2 and thus yielding an impressive fill factor (FF) of 82.8%. Eventually, a power conversion efficiency (PCE) of 20.1% is achieved in the SrFx‐based solar cell. Moreover, in the n‐Si/SrFx/LiF/Al contact, the diffusion of Li in the SrFx film favors facilitating electron transport as well as relaxing its thickness restriction, inhibiting carrier recombination. And an impressive FF of 83.7% with a low ρc of 25.9 mΩ cm2, an improved open‐circuit voltage of 631 mV, and a short‐circuit current density of 39.9 mA/cm2 are attained, resulting in a champion PCE of 21.1%. Double‐layer SrFx/LiF deposited by a simple process provides a grand opportunity to fabricate low‐cost and high‐PCE photovoltaic devices.