Intraband transitions at a CsPbBr₃/GaAs heterointerface in a two-step photon upconversion solar cell

Two-step photon upconversion solar cells (TPU-SCs) based on III-V semiconductors can achieve enhanced sub-bandgap photon absorption because of intraband transitions at the heterointerface. From a technological aspect, the question arose whether similar intraband transitions can be realized by using perovskite/III-V semiconductor heterointerfaces. In this article, we demonstrate a TPU-SC based on a CsPbBr₃/GaAs heterointerface. Such a solar cell can ideally achieve an energy conversion efficiency of 48.5% under 1-sun illumination. This is 2.1% higher than the theoretical efficiency of an Al_0.3Ga_0.7As/GaAs-based TPU-SC. Experimental results of the CsPbBr₃/GaAs-based TPU-SC show that both the short-circuit current J_SC and the open-circuit voltage V_OC increase with additional illumination of sub-bandgap photons. We analyze the excitation power dependence of J_SC for different excitation conditions to discuss the mechanisms behind the enhancement. In addition, the observed voltage-boost clarifies that the J_SC enhancement is caused by an adiabatic optical process at the CsPbBr₃/GaAs heterointerface, where sub-bandgap photons efficiently pump the electrons accumulated at the heterointerface to the conduction band of CsPbBr₃. Besides the exceptional optoelectronic properties of CsPbBr₃ and GaAs, the availability of a CsPbBr₃/GaAs heterointerface for two-step photon upconversion paves the way for the development of high-efficiency perovskite/III-V semiconductor-based single-junction solar cells.