Engineering More Efficient Solar Cells: Perovskite and TPVs

Photovoltaic (PV) technology is becoming more efficient, accessible, and sustainable. Traditional silicon panels are constantly improving with breakthroughs, allowing broader light absorption. The game changers, however, are emerging technologies such as perovskites and thermophotovoltaics.

 

Perovskite solar cell. Image used courtesy of National Renewable Energy Laboratory

 

Perovskites offer higher efficiencies than silicon, making solar panels compact and more appealing. Researchers are tackling stability and manufacturing challenges to make perovskite cells commercially available. Thermophotovoltaics (TPV) is still a relatively new technology. It relies on converting heat or infrared radiation to electricity, making PVs suitable for powering satellites or utilizing waste heat from industries.

 

Improving the Stability and Efficiency of Perovskite PVs

Perovskite solar panel efficiency drops with increasing surface area. Larger areas provide more space for defects and imperfections within the perovskite film. The defects function as traps for charge carriers, hindering their movement and reducing the overall cell efficiency. In addition, perovskite films are prone to degradation caused by moisture, light, and heat. During manufacturing, deposition can be less uniform across the surface area, further contributing to imperfections and instability.

Researchers at Northwestern University, the Institute of Chemical Sciences and Engineering (EPFL), and other institutes tackle these issues by adding thermotropic liquid crystals to protect the panels’ surface area from environmental degradation and increase stability.

In manufacturing processes like evaporative precipitation, additives aggregate within the film during solvent evaporation and hinder the movement of charge carriers. The additive by the Northwestern University researchers avoids this aggregation with thermotropic liquid crystals. The additive will remain liquid even when perovskite solidifies, ensuring uniform passivation and facilitating the movement of charge carriers.

The researchers tested their additive and achieved a fast scan efficiency of 21.8% and a stabilized efficiency of 21.1% for 30 cm2 perovskite mini modules. The quick scan efficiency refers to the measurement taken in controlled laboratory conditions, while the stabilized efficiency is measured after the panel has been exposed to several hundred hours of sunlight.

 

New Figure of Merit for Thermophotovoltaics

Thermophotovoltaics are assessed with two metrics: power density and efficiency. However, unlike standardized light sources used in photovoltaic testing, TPV systems operate under varying heat sources. In Spain, researchers from the Institute of Photonic Sciences (ICFO) point out the lack of standardized operating conditions like source temperature.

 

The concept of thermophotovoltaic cells (left). Recent works in TPV devices assessed by new metric (right). Image used courtesy of SPIE

 

They introduce a new figure of merit, considering temperature dependencies for the trade-off between power density and efficiency. While achieving high conversion efficiency is desirable, absorbing enough heat is equally important. Optimizing both aspects is crucial. Previous studies have also suggested that reduced ohmic losses may result in high TPV efficiency, which comes at the cost of reduced power density. The new metric allows meaningful comparisons across different TPV systems and operating conditions.