Organic-inorganic lead halide perovskite has become one of the most attractive materials for future low-cost high-efficiency solar technology. However, the polycrystalline nature of perovskite thin-film often possesses an exceptional density of defects, especially at grain boundaries (GBs) and film surface, limiting further improvement in the power conversion efficiency (PCE) of the perovskite device. Here, we report a simple method to reduce GBs and to passivate the surface of a methylammonium lead triiodide (MAPbI3) film by guanidinium thiocyanate (GUTS)-assisted Ostwald ripening post treatment.High-optoelectronic quality MAPbI3 film consisting of micron-sized grains were synthesized by posttreating a MAPbI3 film with GUTS/isopropanol solution (4 mg/mL, GUTS-4). Analysis of the electrochemical impedance spectra (EIS) of the solar cells showed that interfacial charge recombination resistance of the device based on a GUTS-4 post-treated MAPbI3 absorber film was increased by a factor of 1.15 to 2.6, depending on light illumination intensity, compared to the control MAPbI3 cell. This is consistent with results of the open-circuit voltage (Voc) decay and the light intensity dependent photovoltage evolution which shows device with GUTS treatment had longer charge carrier lifetime and was more ideal (ideality factor=1.25). Further characterization by Kelvin probe force microscope indicated that GUTS-4 treatment shifted the energetics of the MAPbI3 film by ~100 meV towards better energy level alignment with adjacent SnO2 electron transport layer, leading to a more favorable charge extraction process at the MAPbI3/SnO2 interface. As a result, the PCE of PSCs was enhanced from 14.59% to 16.37% and the hysteresis effect was mitigated.

19% perovskite solar cells with enhanced electronic properties of MAPbI3film through employing 2.5% PbCl2additive in the precursor.

In this work, we have developed a new efficient hole transport material (HTM) composite based on poly(3-hexylthiophene) (P3HT) and bamboo-structure carbon nanotubes (BCN) for CH 3 NH 3 PbI 3 (MAPbI 3 ) based perovskite solar cells. Compared to pristine P3HT, it is found that the crystallinity of P3HT was significantly improved by addition of BCN, which led to over one order of magnitude higher conductivity for the composite containing 1-2wt% BCN in P3HT. In the meantime, the interfacial charge transfer between the MAPbI 3 light absorbing layer and the HTM composite layer based on the P3HT/BCNs was two-fold faster than pristine P3HT. More importantly, the HTM film with superior morphological structure consisting of closely compact large grains was achieved with the composite containing 1wt% BCNs in P3HT. The study by electrochemical impedance spectroscopy has confirmed that the electron recombination in the solar cells was reduced nearly ten-fold with the addition of 1wt% carbon nanotubes in the HTM composite. Owing to the superior HTM film morphology and the significantly reduced charge recombination, the energy conversion efficiency of the perovskite solar cells increased from 3.6% for pristine P3HT to 8.3% for P3HT/(1wt% BCNs) with a significantly enhanced open circuit voltage (V oc ) and fill factor (FF). The findings of this work are important for development of new HTM for high performance of perovskite solar cells.

Current-voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu + )-dopant is demonstrated to tailor the crystal structure of mixed-cation formamidinium-cesium lead triiodide (FA 0.83 Cs 0.17 PbI 3 ) perovskite, resulting in an improved energy conversion efficiency and tunable current-voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu-dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%-Gu-dopant, then changed to inverted hysteresis with a higher Gu-dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu + -dopant, the optimal content of 2% Gu + -dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination.

Organic-inorganic hybrid lead halide perovskite solar cells have demonstrated competitive power conversion efficiency over 22%; nevertheless, critical issues such as unsatisfactory device stability, serious current-voltage hysteresis, and formation of photo nonactive perovskite phases are obstacles for commercialization of this photovoltaics technology. Herein we report a facial yet effective method to hinder formation of photoinactive δ-FAPbI and hysteresis behavior in planar heterojunction perovskite solar cells based on K (MAFA)PbIBr (0≤ x ≤ 0.1) through incorporation of potassium ions (K). X-ray diffraction patterns demonstrate formation of photoinactive δ-FAPbI was almost completely suppressed after K incorporation. Density functional theory calculation shows K prefers to enter the interstitial sites of perovskite lattice, leading to chemical environmental change in the crystal structure. Ultrafast transient absorption spectroscopy has revealed that K incorporation leads to enhanced carrier lifetime by 50%, which is also confirmed by reduced trap-assisted recombination of the perovskite solar cells containing K in photovoltage decay. Ultraviolet photoelectron spectroscopy illustrates that K incorporation results in a significant rise of conduction band minimum of the perovskite material by 130 meV, leading to a more favorable energy alignment with electron transporting material. At the optimal content of 3% K (molar ratio, relative to the total monovalent cations), nearly hysteresis-free, enhanced power conversion efficiencies from 15.72% to 17.23% were obtained in this solar cell.