Conformal quantum dot-SnO2 layers as electron transporters for efficient perovskite solar cells.

Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous-titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid-stabilized tin(IV) oxide quantum dots (paa-QD-SnO2) on the compact-titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL-perovskite interface. The use of paa-QD-SnO2 as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively.

Vapor-assisted deposition of highly efficient, stable black-phase FAPbI3 perovskite solar cells.

Mixtures of cations or halides with FAPbI3 (where FA is formamidinium) lead to high efficiency in perovskite solar cells (PSCs) but also to blue-shifted absorption and long-term stability issues caused by loss of volatile methylammonium (MA) and phase segregation. We report a deposition method using MA thiocyanate (MASCN) or FASCN vapor treatment to convert yellow δ-FAPbI3 perovskite films to the desired pure α-phase. NMR quantifies MA incorporation into the framework. Molecular dynamics simulations show that SCN- anions promote the formation and stabilization of α-FAPbI3 below the thermodynamic phase-transition temperature. We used these low-defect-density α-FAPbI3 films to make PSCs with >23% power-conversion efficiency and long-term operational and thermal stability, as well as a low (330 millivolts) open-circuit voltage loss and a low (0.75 volt) turn-on voltage of electroluminescence.

Poly(ethylene glycol)-[60]Fullerene-Based Materials for Perovskite Solar Cells with Improved Moisture Resistance and Reduced Hysteresis.

A series of [60]fullerenes covalently functionalized with the polymer poly(ethylene glycol) is presented. These new [60]fullerene-based materials have been incorporated as additives in CH3 NH3 PbI3 (MAPbI3 ), the most common organic-inorganic perovskite used in perovskite solar cells. The extensive photovoltaic study performed by using these materials shows several beneficial effects on the performance of these cells, including a reduction in hysteresis and an increased stability against moisture, whereby the solar cells retain up to 97 % of their initial power conversion efficiency in an ambient atmosphere.

Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance.

All of the cations currently used in perovskite solar cells abide by the tolerance factor for incorporation into the lattice. We show that the small and oxidation-stable rubidium cation (Rb+) can be embedded into a "cation cascade" to create perovskite materials with excellent material properties. We achieved stabilized efficiencies of up to 21.6% (average value, 20.2%) on small areas (and a stabilized 19.0% on a cell 0.5 square centimeters in area) as well as an electroluminescence of 3.8%. The open-circuit voltage of 1.24 volts at a band gap of 1.63 electron volts leads to a loss in potential of 0.39 volts, versus 0.4 volts for commercial silicon cells. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full illumination and maximum power point tracking.