Charge-Carrier Balance for Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells

The DMF-treated PEDOT:PSS and PMMA-modified PCBM were employed as the HSC and ESC, respectively, to establish charge-carrier balance in the inverted PHJ PSCs. The DMF treatment helps to enhance the conductivity of PEDOT:PSS film and reduce its surface roughness, which facilitates the interfacial contact between the perovskite layer and HSC. PEDOT:PSS was spin coated onto a clean ITO substrate at 3000 rpm for 30 s and annealed at 130°C for 20 min in the air. After it was cooled down to room temperature, 60 μL DMF was dropped onto the film for 5 s, and then spun off at 3000 rpm for 30 s. Next, MAI and the dehydrated Pb(Ac)₂ were dissolved in anhydrous DMF at a 3:1 molar ratio with 1.0 mol% MABr additive. The precursor solution was spin coated onto the PEDOT:PSS layer at 4000 rpm for 40 s and then compact and well-crystallized CH₃NH₃PbI₃ films (300 nm) were obtained. The interface engineering of HSC and ESC resulted in accelerated and balanced charge-carrier transport in the device, leading to the suppressed charge-carrier accumulation and recombination.