Reducing energy loss and stabilising the perovskite/poly (3-hexylthiophene) interface through a polyelectrolyte interlayer

Efficient hole transport materials in n-i-p structured perovskite solar cells (PSCs) have been confined to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) and poly(triarylamine) (PTAA). However, the need for hygroscopic dopants has limited improvements in the stability of the devices. Here, we have successfully fabricated stable PSCs using a dopant-free poly (3-hexylthiophene) (P3HT) HTL. Through introducing a polyelectrolyte buffer layer (P3CT-BN), the P3HT film morphology, perovskite built-in electric field, surficial defects and the hole transfer speed were all optimized, along with significant suppression of interfacial recombination. Hence, the efficiency was improved from 13.13% to 19.23%, with a substantially improved V_OC from 0.90 V to 1.10 V and FF from 63.1% to 74.2%. Simultaneously, the un-encapsulated devices also exhibited improved stability, retaining 80% of the peak PCE in the atmosphere (50% relative humidity) for 2300 h or heating at 85 °C in N₂ for 400 h and 79% of the original PCE under simultaneous damp heat (60 °C/60-70% humidity) in air.