Despite the exceptional efficiency of perovskite solar cells (PSCs), further improvements can be made to bring their power conversion efficiencies (PCE) closer to the Shockley-Queisser limit, while the development of cost-effective strategies to produce high-performance devices are needed for them to reach their potential as a widespread energy source. In this context, there is a need to improve existing charge transport layers (CTLs) or introduce new CTLs. In this contribution, we introduced a new polyelectrolyte (lithium poly(styrene sulfonate (PSS))) (Li:PSS) polyelectrolyte as an HTL in inverted PSCs, where Li+ can act as a counter ion for the PSS backbone. The negative charge on the PSS backbone can stabilize the presence of p-type carriers and p-doping at the anode. Simple Li:PSS performed poorly due to poor surface coverage and voids existence in perovskite film as well as low conductivity. PEDOT:PSS was added to increase the conductivity to the simple Li:PSS solution before its use which also resulted in lower performance. Furthermore, a bilayer of PEDOT:PSS and Li:PSS was employed, which outperformed simple PEDOT:PSS due to high quality of perovskite film with large grain size also the large electron injection barrier (ϕe ) impeded back diffusion of electrons towards anode. As a consequence, devices employing PEDOT:PSS / Li:PSS bilayers gave the highest PCE of 18.64%.
Keywords: hole transport layer; perovskite; polyelectrolyte; solar cell.
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