PaA – Partnership Area

Nanotextured perovskite devices have led to tremendous advancements in various fields, including light emitting diodes and solar cells. For example, at Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) perovskite–silicon tandem solar cells (PSTSC) have been investigated as they allow to overcome the power conversion efficiency limit of conventional silicon solar cells. In recent experiments nanotextured tandem devices, showed various advantages:

 

To a surprising degree the success of nanotextured perovskite–silicon tandem solar cells remains a mystery. It was noted experimentally that the open-circuit voltage for textured cells is higher than for planar cells. While a higher open-circuit voltage is beneficial for device performance, it is not understood theoretically. Understanding the reason is key to further improving the cell design. In contrast to other semiconductor materials such as silicon, in perovskites it is crucial to take ion movement into account.

Our numerical results revealed that texturing redistributed the electric field, influencing carrier accumulation and recombination dynamics. We found that moderate texturing heights (≤ 300 nm) always increased the power conversion efficiency, regardless of surface recombination velocities. Our project also clarified why experiments had reported that texturing both increased and reduced open-circuit voltages in perovskite solar cells: this behaviour originated from variations in surface recombination at the untextured electron transport layer. In contrast, surface recombination at the textured hole transport layer strongly affected the short-circuit current density, with lower recombination rates keeping it closer to the optical ideal. These findings provided new insights into the opto-electronic advantages of texturing and offered guidance for the design of next-generation textured perovskite-based solar cells, light emitting diodes, and photodetectors.

 

These results were achieved by coupling Maxwell’s equations with charge-transport drift-diffusion equations. For the optical simulations, we numerically solved the time-harmonic wave equation as derived from Maxwell’s equations, formulated as a scattering problem. We used the finite element method as implemented in the software JCMsuite. For the charge transport simulations, we employed a vacancy-assisted drift-diffusion model that took ionic vacancies in the perovskite material into account. These equations were solved using a time-implicit finite volume scheme with the excess chemical potential flux scheme for the current density approximation, as implemented in ChargeTransport.jl.