Flexible perovskite solar cells (f-PSCs) have recently reached power conversion efficiency (PCE) as high as 25.09 % [1] which is reaching their rigid counterparts on glass, which in very short time have achieved 26.1% of certified efficiency. The use of flexible substrates however, thanks to the high power/to weight ratio generated which is the range of 29.4 W/g compared to 8.31 W/g for amorphous silicon and 0.254 W/g for ultra-thin CdS / CdTe [2-3], opens up to a wide range of applications, from sensors for the Internet of Things, to the retrofitting of existing buildings to improve their energy efficiency (building-applied PV), to space.

The investigation of perovskite solar cells for use in space began in 2015, when Miyazawa et al. irradiated their experimental cells with protons and electrons, and found the perovskite cells retained a larger portion of their photovoltaic parameters than the silicon and III-V cells tested on the same experiment [4]. After this initial finding, more irradiation experiments were run, showing similarly high resilience of PSCs to particle radiation, consolidating the interest for space applications of this technology and as the focus broadened to other damage sources present in the space environment, such as atomic oxygen [5] , vacuum,  [6], or  gamma radiation [7].

Considering particle radiation ageing tests have also started to include resilience to neutrons, which unlike protons and electrons are not electrically charged, and therefore do not directly cause ionization effects in an irradiated material. However, the mass of a neutron however is still significant enough to cause elastic collisions with atoms in the targeted material [8], which can displace nuclei, leaving defects in the lattice [9]. Characterizing the entity of this damage in perovskite solar cells aimed at space applications therefore is important as neutrons are present in various space environments, such as around spacecrafts, whether in orbit or interplanetary travel , or other planets atmospheres [10-11].

In this talk we will give an overview on the effects of neutron irradiation on flexible perovskite solar cells focussing on the role of the hole transporting layers in a NIP configuration [12]. In particular, we will show how the substitution of standard spiro-OMeTAD with P3HT-modified and PTAA-modified polymers affects the overall performances of the unencapsulated devices revealing an higher resilieance of the polymer based system respect to spiro-OMeTAD under neutron irradiation.