Perovskite-based solar cells have attracted a great attention in the last 10 years due to their excellent optoelectronic properties. Currently, the power conversion efficiencies of solar devices using these materials have exceeded 25% for single junctions and 29% in tandem structures with silicon. Record results were obtained on small areas in the order of 1 cm².

For some applications, the use of flexible substrates may be attractive for single-junction perovskite technology as it opens the way to high-speed, low-temperature printing processes. Thus, it becomes possible to use low cost substrates whereas inorganic flexible technologies, such as CIGS, require higher temperature processes and substrates that are more expensive.

Many teams around the world are trying to meet the challenges of making larger area devices with sufficient stability for real-life applications. This is one of the tasks that have set to themselves partners of the European APOLO project, in which CEA obtained these results.

These flexible perovskite solar modules have been obtained at low temperature on low cost substrates (PET) and with a very simple structure composed of 5 layers including electrodes. The displayed performances are obtained after encapsulation (also flexible). The stability of these devices has been tested under damp heat conditions (85°C, 85%RH), according to the standards used in silicon technologies. A stability of several hundreds of hours was obtained (400 to 800h according to encapsulation) considering a standard objective of 1000h.

To achieve this result, the CEA has worked on

- The optimization of the stack of layers that make up the cell,

- The use of a 3-step laser process to produce the module

- The development of a flexible encapsulation process that is fully compatible with highly gas-barrier materials, without performance initial loss.

The European APOLO project (European Union's Horizon research and innovation programme under grant agreement No 763989), which finances this work, is coming to an end.

Modules will be interconnected in series to obtain high voltages and will be tested according to building standards by Flexbrick company, member of Apolo consortium. In addition, stability tests of encapsulated flexible modules under real outdoor conditions are currently being carried out.

In addition, these modules are currently being tested at the Fraunhofer Institute ISE, also a partner in the APOLO project, for indoor applications. These tests already showed power conversion efficiencies of up to 24.5% at very low illumination (500 lux). Certification is being considered.