Intraband transitions at a CsPbBr/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 CsPbBr/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 AlGaAs/GaAs-based TPU-SC. Experimental results of the CsPbBr/GaAs-based TPU-SC show that both the short-circuit current J and the open-circuit voltage V increase with additional illumination of sub-bandgap photons. We analyze the excitation power dependence of J for different excitation conditions to discuss the mechanisms behind the enhancement. In addition, the observed voltage-boost clarifies that the J enhancement is caused by an adiabatic optical process at the CsPbBr/GaAs heterointerface, where sub-bandgap photons efficiently pump the electrons accumulated at the heterointerface to the conduction band of CsPbBr. Besides the exceptional optoelectronic properties of CsPbBr and GaAs, the availability of a CsPbBr/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.