Bipolar polymer networks in perovskite films by in-situ cross-linking for smoother carrier transportation and enhanced stability in photovoltaic devices

Designed a bipolar monomer V–O-8FTPB with D-A structure and styrene groups. • In-situ crosslinked with TEMPIC during annealing to form a polymer network enabling ambipolar transport. • PCE improved from 20.76% to 23.04%, with only 11% degradation after 3000 h at 60–70% relative humidity (RH). Perovskite solar cells (PSCs) have been developed intensively with the rocketing power conversion efficiency (PCE). However, the moisture and thermal instability primarily hinders their practical application, calling for essential crystal bulk and interface protections. Herein a novel cross linkable bipolar semiconductor material, N,N′-diphenyl-N,N′-bis(4-(4-vinylbenzyloxy)phenyl)-2,2′,3,3′,5,5′,6,6′-octafluoro-1,1′-biphenyl-4,4′-diamine (V–O-8FTPB), was designed for perovskite additive engineering. Specifically, this monomer incorporates styrene terminals for crosslinking, as well as the core of fluorinated biphenyl and triphenylamine as respective n-type and p-type moieties. The crosslinking happened during precursor annealing for perovskite crystallization with the aid of another crosslinking agent tri[2-(3-mercaptopropionyl) ethyl]isocyanurate (TEMPIC). A polymer network wrapping perovskite grains was thus constructed. Such modification on grain boundaries and surfaces endowed defect suppression and reinforced resistance against moisture and further harsh liquid-heat damage. Notably, the bipolar V–O-8FTPB better matched the bipolar transporting of perovskites, neither impeding hole nor electron transport. The optimized photovoltaic device with an active area of 0.09 cm 2 delivered a champion PCE of 23.04%. Furthermore, the encapsulated devices retained 90% of initial efficiency after immersion in water for 72 h, or only 17% decay after 48 h in the 85 °C hot water. This work highlights a novel criteria of bipolar monomer design for in-situ cross-linkable additives to enable the framework charge transport and great hydrophobicity. Download: Download high-res image (335KB) Download: Download full-size image