From pv magazine Global
While scientists have quickly pushed the efficiency of perovskite solar cells to levels that rival or even surpass some of today’s commercial technologies, gaining a full understanding of all the mechanisms at work within the material will be a much longer process.
The role of defects in perovskite material structures is currently one of the most studied areas here. Such defects are thought to be the main limiting factors in both performance and stability of perovskite solar cells. And while different types of passivation – where a coating is applied to limit the activity of defects – have been used successfully, the mechanisms by which these defects affect solar cell performance are not fully understood, and a closer look at them could open up even more effective strategies.
Taking such a closer look was the goal of a group of scientists led by China’s Peking University, who investigated a method using additives to control the perovskite’s dielectric properties, and demonstrate the creation of a screening effect that limits the influence of defects on solar cell performance. “Such an effect lowers the possibility that carriers are trapped in defects, thus, even if the defects still exist, they are, to some extent, “invisible” to charge carriers…,” the group explained. “Based on these improvements, nonradiative recombination pathways can be considerably suppressed.”
Working with an inverted perovskite solar cell device made from formamidinium-cesium lead halide, the group used this approach to fabricate a 22.3% efficient solar cell with 1.25 V open-circuit voltage, and also provide new insights into where voltage losses occur between the perovskite film and the PV device. The work is described in full in the paper Dielectric screening in perovskite photovoltaics, published in Nature Communications.
“The accelerated dielectric response of the film not only greatly improves the optoelectronic properties of the perovskite but also boosts the power conversion efficiency…” the group explained. “…further quantitative analysis in the voltage loss provides a clear understanding of the different origins of nonradiative losses and corresponding contributions.”
With these insights into how various particles interact with each other deep within a perovskite material, the group expects to unlock several new pathways for researchers to bring perovskite solar cells even closer to their theoretical efficiency limits. “This work provides a new paradigm to mitigate the adverse effect of defects from different angles,” they conclude, “which will open a new avenue to further minimise nonradiative recombination losses in perovskite photovoltaics by dielectric regulation.”
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