Dielectric Junction: Electrostatic Design for Charge Carrier Collection in Solar Cells

Conventional solar cells typically use doping of the involved semiconducting layers and work function differences between highly conductive contacts for the electrostatic design and the charge selectivity of the junction. In some halide perovskite solar cells, however, substantial variations in the permittivity of different organic and inorganic semiconducting layers strongly affect the electrostatic potential and thereby indirectly also the carrier concentrations, recombination rates, and eventually efficiencies of the device. Here, numerical simulations are used to study the implications of electrostatics on device performance for classical p−n junctions and p−i−n junctions, and for device geometries as observed in perovskite photovoltaics, where high‐permittivity absorber layers are surrounded by low‐permittivity and often also low‐conductivity charge transport layers. The key principle of device design in materials with sufficiently high mobilities that are still dominated by defect‐assisted recombination is the minimization of volume with similar densities of electrons and holes. In classical solar cells this is achieved by doping. For perovskites, the concept of a dielectric junction is proposed by the selection of charge transport layers with adapted permittivity if doping is not sufficient. Doped p−n junctions represent the prototype of solar cells in text books, while p−i−n junctions support charge carrier collection for low‐quality absorbers. For halide‐perovskite cells the design via doping is challenging and substantial permittivity variations occur. The concept of the dielectric junction is introduced and designs electrostatics, recombination, and performance of solar cells by selecting materials with certain permittivities.