Research Blogs
Photon recycling in perovskite solar cells assessed by a detailed-balance compatible dipole emission model
In solar cells, photon recycling leads to an increase in the open-circuit voltage of the device. This tutorial explains how to exploit self-absorption to increase the efficiency of the solar cell.
Fitting routine for a reliable transient photoluminescence simulation of perovskite films
Transient photoluminescence (trPL) characterization experiments allow to analysis charge carrier dynamics and identify the recombination channels of the device structure under investigation.
Useful information that can be extracted includes the quantification of radiative and non-radiative lifetimes, charge carrier extraction from differential lifetime computation, and the influence of the interfaces on the recombination mechanism. Fitting the experimental results with simulations further supports the analysis of the obtained data. However, qualitatively comparable fittings can be obtained with different sets of simulation parameters.
Using the fully-coupled, 1-dimensional optoelectronic simulation software Setfos, the trPL signal of a simple glass/perovskite structure was simulated and a routine is suggested to ascertain the reliability of the results. This routine is based on experimentally measured material properties and the analysis of the band diagram evolution during the photoluminescence transient. The validity of the simulated trPL is also recursively verified by fitting the decay with a bi-exponential function to extract the lifetimes of the recombination mechanisms.
How to quantify Non-radiative voltage losses and recombination in solar cells
The open-circuit voltage (Voc) is the electrical potential difference between the two terminals of a solar cell, when there is no external load applied, hence no electric current flows. Correspondingly, this means that, when a voltage equivalent to the Voc is applied to the terminals of the solar cell, the recombination current (Jrec, which typically follows a non-ideal diode equation) and the photocurrent (Jph, the current generated by illuminating the solar cell) are equal, hence the net current is zero (Jrec=Jph at V= Voc).
Solar cells often present also non-radiative recombination mechanisms, in addition to the radiative one, as a result of poor material quality and non-idealities. To increase the Voc and thus potentially the power conversion efficiency, it is necessary to minimize the ΔVoc,nrad. It is, therefore, necessary to quantify the total loss and determine its origin.
Electroluminescence (EL) and photoluminescence quantum yield (PLQY) allow to directly extract the ΔVoc,nrad for thin-film solar cells such as perovskite solar cells, kesterite, perovskite, organic, or quantum dot. solar cells.
After quantifying the losses, the combination of capacitance-voltage (CV), temperature-dependent voltage characteristics (JV-T), and capacitance-frequency (Cf-T) measurements are essential to identify the recombination mechanisms.
Why Perovskite Solar cells with High Efficiency Show Small iV-curve Hysteresis
In many perovskite solar cells, hysteresis is observed between the forward and reverse current-voltage (IV) scans. This IV curve hysteresis can be problematic for the correct determination of the Power Conversion Efficiency (PCE). While the exact origin of the IV curve hysteresis has remained a topic of debate, it is now widely accepted that mobile ions are the principal cause. However, it is still the subject of ongoing debates about how exactly mobile ions influence the device operation.
In this blog, we are showing how a proper drift-diffusion simulation can help in understanding how mobile ions are affecting the JV characteristics of a perovskite solar cell.