Suppressing nonradiative recombination at the interface between the organometal halide perovskite (PVK) and the charge‐transport layer (CTL) is crucial for improving the efficiency and stability of PVK‐based solar cells (PSCs). Here, a new bathocuproine (BCP)‐based nonconjugated polyelectrolyte (poly‐BCP) is synthesized and this is introduced as a “dual‐side passivation layer” between the tin oxide (SnO2) CTL and the PVK absorber. Poly‐BCP significantly suppresses both bulk and interfacial nonradiative recombination by passivating oxygen‐vacancy defects from the SnO2 side and simultaneously scavenges ionic defects from the other (PVK) side. Therefore, PSCs with poly‐BCP exhibits a high power conversion efficiency (PCE) of 24.4% and a high open‐circuit voltage of 1.21 V with a reduced voltage loss (PVK bandgap of 1.56 eV). The non‐encapsulated PSCs also show excellent long‐term stability by retaining 93% of the initial PCE after 700 h under continuous 1‐sun irradiation in nitrogen atmosphere conditions.

The degradation of the perovskite layer in atmospheric air is a critical bottleneck for the commercialization of perovskite solar cells (PSCs). As the moisture and oxygen in air penetrate the charge transport layer/top metal electrode interface, both adjacent layers and perovskite layers decompose in the PSCs. Herein, moisture‐stable inverted PSCs (I‐PSCs) based on methylammonium lead triiodide (MAPbI3) by introducing amine‐functionalized small molecules as metal adhesive layers (MALs) between the electron transport layer (ETL) and metal electrode (here, Cu) are demonstrated. A strong coordination bond of CuN forms at the Cu/MAL interface, leading to the layer–layer growth mode for the dense formation of Cu electrodes with a strong adhesion to the ETL. Thus, this modified electrode prevents the ingress of moisture into the I‐PSCs, resulting in outstanding moisture stability; the efficiency of I‐PSCs retains 90% of the initial efficiency after 200 days of exposure to atmospheric air (25 °C, relative humidity [RH] ≈20–40%). Under harsher conditions (e.g., 25 °C/RH65%, 25 °C/RH85% and immersion in water) for a considerable time period, the modified I‐PSCs manifest relatively no degradation compared with the pristine I‐PSCs. It is believed that this breakthrough provides a significant impact on improving the stability of I‐PSCs.

We report the small molecules utilizing new electron-deficient unit, 2,2-dimethyl-2H-benzimidazole (MBI) and phenanthro[9,10-c][1,2,5]thiadiazole (PT), for the photovoltaic application. Donor-acceptor-donor (D-A-D) types of conjugated small molecules containing benzo[1,2-b;3,4-b']dithiophene (BDT) as electron rich unit and MBI and PT as electron deficient units (SM1 and SM2) were synthesized. D-A-D type of small molecules has the abilities of increasing intramolecular charge transfer (ICT) inducing long wavelength absorption and lowering the HOMO level for the improvement of open-circuit voltage (V OC ). SM1 was synthesized by coupling BDT and PT units by Stille coupling reaction with Pd(0)-catalyst. By using same type of Pd(0)-catalized reaction, BDT unit and MBI unit linked with two thiophenes were coupled to provide SM2. The spectrum of SM2 in the solid thin film shows absorption band with maximum peak at 601 nm and the absorption onset at 756 nm, corresponding to band gap of 1.64 eV. The device comprising SM2 with PCBM (3:7) showed a V OC of 0.62 V, a J SC of 1.69 mA/cm 2 , and a fill factor (FF) of 0.27, giving a power conversion efficiency of 0.28%.

No abstract

We report new random copolymers using the electron-deficient unit N-alkyl-2,2 0 -bithiophene-3,3 0 -dicarboximide (BTI) for organic solar cells. For absorption over a broader range of the solar spectrum, push-pull types of conjugated polymers PBTIBDT-3, PBTIBDT-5, and PBTIBDT-7, containing 4,8-bis(2-octyldodecyloxy) benzo[1,2-b;3,4-b']dithiophene (BDT) as electron-pushing unit and BTI as electron-pulling unit, were synthesized. The polymers were synthesized by coupling electron-pushing and electron-pulling units by Stille polymerization with Pd(0) catalyst. The incorporation of more BTI units induced more red shift of the absorption spectra of the polymer thin films. The device comprising PBTIBDT-5 and PC 71 BM (1:1) showed V OC = 0.76 V, J SC = 3.28 mA/cm 2 , and fill factor (FF) = 0.51, giving a power conversion efficiency of 1.26%.