Two TPB-based HTMs were synthesized and their energy levels were tuned to match with perovskite by introducing electron-donating groups asymmetrically. The TPBC based doping-free perovskite solar cell afforded an impressive PCE of 13.10% under AM 1.5G illumination, which is the first case of an effective device with TPB-based doping-free HTMs.

Novel small-molecule hole transporting materials (HTMs) with a linear π-conjugated structure have been synthesized. The perovskite solar cell based on 2TPA-2-DP as the HTM exhibits an encouraging power conversion efficiency of 9.1% under AM 1.5 G (100 mW cm⁻²) illumination, which is the first demonstration of an effective perovskite solar cell using a linear structured HTM.

The stability of perovskite solar cells is still one issue that needs to be solved, though remarkable success has been achieved since its first report in 2009. In this work, two thiadiazole derivatives (1,3,4-thiadiazolidine-2-thione, TDZT and 1,3,4-thiadiazolidine-2,5-dithione, TDZDT) were added into a perovskite precursor to modulate CH₃NH₃PbI₃ perovskite crystal growth. Thiadiazole derivatives can allow the size of the CH₃NH₃PbI₃ crystals to exceed 800 nm and can reduce the grain boundaries. The defect density, calculated using the space charge limited current (SCLC) method for perovskite, was 7 times lower when a certain amount of TDZDT was added. As a result, we obtained a power conversion efficiency (PCE) of 19.04% accompanied by excellent stability under humidity and heat. The unsealed devices retained 91.2% of their initial PCE after 1200 h in 65 ± 5% relative humidity at room temperature under dark conditions, and over 90% of their initial PCE after 840 h of aging in 30% relative humidity and ambient air at 60–75 °C under dark conditions. The result showed that these thiadiazole derivatives can effectively suppress the defects, thus improving the efficiency and stability of the perovskite solar cells.