Despite the rapid development of perovskite solar cells several challenges remain. A deeper understanding of the main losses, and how to mitigate them, is needed to make targeted improvements possible. In this talk, I will discuss our drift-diffusion modelling approach to shed new light on these fascinating solar cell materials.

Drift-diffusion techniques make it possible to connect and explain the fundamental generation, transport and extraction processes to macroscopic device performance. If done right, one can also do the opposite: By reverse-engineering current-voltage measurements on actual solar cells, one can identify the limiting factors. As an example, we show how current-voltage data and electroluminescence measurements help us identify the voltage losses in a series of co-evaporated FACsPbIBrCl perovskite solar cells with organic transport layers.

The physical processes underlying the impedance response of perovskite solar cells are not well understood. Typically, the low-frequency peak in such impedance spectra is attributed to ion dynamics, while the high-frequency peak is associated with electronic processes.

We introduce a new formula which enables us to directly derive the ion diffusion coefficient from the impedance response of perovskite solar cells. The validity of this formula is confirmed through extensive drift-diffusion simulations.

Upon demonstrating this, we determine the ion diffusion coefficients of a MAPI and a FAMAPI solar cells. The obtained diffusion coefficients are consistent with previously reported values from other characterization techniques. The advantage of this method is that it facilitates the precise, rapid, and straightforward determination of the ion diffusion coefficients.

Next, we introduce an experimental method for identification of the limiting aspect of perovskite solar cells under operating conditions in terms of recombination losses. We illuminate a bifacial cell from both sides separately with either red, blue or white light, each absorbed differently in the cell depending on the position in the device. Using the fill factor from the device characteristics for each case taking into account the direction of illumination we are able to accurately identify which part of the cell is limiting the performance. We show that this holds for many typical perovskite solar cells using drift-diffusion simulations. Finally, we issue a protocol to determine the dominant recombination channel under operating conditions in full device configuration.