Perovskites for solar energy

The easy preparation of perovskites allows their properties to be tuned in order to optimise solar-to-electricity conversion efficiency. In a real device, electrical charges (electrons and holes) need to be transferred with minimal loss across interfaces with other materials, in particular, the cheap and abundant titanium dioxide. Therefore, describing the interfacial charge transfer is of crucial importance. Finally, the lifetime of a solar cell is one of its main assets in terms of marketing, and perovskites still need to be optimised in this respect.

The project aimed at achieving an enhanced efficiency and stability of perovskite-based solar cells via improved synthesis, and their detailed, atomic-level characterisation using cutting-edge experimental and theoretical tools. Furthermore, it aimed at optimising the solar energy conversion efficiency and photostability of perovskite-based solar cells.

During the project, a record in conversion efficiency (approx. 21%) was achieved, which has in the meantime been surpassed. To improve cell stability, interface engineering has been developed using low-dimensional perovskites. In terms of characterisation, new behaviours of the charges have been brought to light that may pave the way for novel applications of perovskites as light-emitting devices. The details of charge migration in the materials that have been gathered within this project provide better insights into how the conversion efficiency and stability of perovskite-based solar cells could be improved. In summary:

• Demonstration of an interface engineering method and growth of low dimensional perovskite to improve solar cell stability and efficiency;
• Characterisation of the charge behaviour of single crystals of organic-inorganic perovskites under irradiation by short pulses. Evidence for new quasi-particles under high fluence and precise determination of electron and hole effective masses;
• Development of a novel experimental method to monitor interfacial electron transfer;
• Calculations of effective masses that are largely in agreement with experimental results;
• Clarification of origin of band gap shift with temperature and dual emission.

Implications for research

There is no doubt that the above findings are of great importance for research. The discovery of Mahan excitons is an important milestone, as are the insights gained from calculations.

Implications for practice

The demonstration of a novel interface engineering method and the use of low dimensional perovskites for enhanced stability and conversion efficiency are expected to have a considerable impact.

Preparation and characterization of high efficiency hybrid organic-inorganic thin film solar cells