Relating band edge DOS occupancy statistics associated excited state electron entropy generation to free energy loss and intrinsic Voc deficit of solar cells

Abstract

Ever since the invention of solar cells, thermodynamics has been used to assess their performance limits and investigate advances in materials science and photovoltaic technology to reduce the gap between practical efficiencies and thermodynamic limits to photovoltaic energy conversion. By systematically addressing thermodynamic efficiency losses in current photovoltaics, ultrahigh efficiency photovoltaic can be expected. Currently, the non-radiative recombination of some ultrahigh efficient solar cells is almost completely suppressed, and the radiative recombination loss is the key to restricting the further improvement of device performance. This work relates the energy band edge electronic density of states (DOS) of semiconductor absorber and transport layer, excited/transfer state electronic entropy to thermodynamically inevitable energy loss during photoelectric conversion in solar cells. Through comprehensive theoretical analysis and device simulation, it is revealed why solar cells based on semiconductor material with a low DOS have higher V_oc. On account of the basic limitations of thermodynamic laws on the energy conversion process, this work reveals a hidden variable that affects the photovoltaic performance and puts forward the band edge DOS engineering as a new dimension in performance optimization of solar cells apart from the traditional material and defect passivation engineering, etc. This work highlights the great importance of DOS engineering for further improving the performance of solar cell devices.