Ag:PSS polyelectrolyte/PTB7 bilayers as efficient hole transport layers for perovskite solar cells

By virtue of the exceptional optical and electrical features of organic-inorganic lead-halide perovskites, the power conversion efficiency (PCE) of perovskite solar cells (PeSCs) has surpassed that of commercialized single junction silicon solar cells. Although PeSCs have demonstrated exceptional efficiency, there is still room for improvement to approach the theoretical Shockley-Queisser limit. Additionally, there is a need for the development of cost-effective strategies to produce high-performance devices, enabling PeSCs to fulfill their potential as a widely adopted and sustainable energy source. Considering this, in this work, we've developed a polyelectrolyte (silver poly(styrene sulfonate (PSS)) (Ag:PSS) hole transport layer (HTL), and investigated it in combination with a conjugated polymer,poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]-dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) as a bilayer HTL. Ag:PSS alone performs poorly due to mismatched energy levels at the anode interface, however, when PTB7 is used in combination with Ag:PSS, effective extraction and transport of carriers towards the anode is achieved. PeSCs with optimized bilayer HTLs (Ag:PSS/PTB7) gave PCEs of up to 17.09 %, higher than that of the Ag:PSS alone (reference device 12.13 %) which can be attributed to improved interfacial energetics at the HTL/perovskite interface.