Alexander J. Cimaroli

Employing Lead Thiocyanate Additive to Reduce the Hysteresis and Boost the Fill Factor of Planar Perovskite Solar Cells.

Lead thiocyanate in the perovskite precursor can increase the grain size of a perovskite thin film and reduce the conductivity of the grain boundaries, leading to perovskite solar cells with reduced hysteresis and enhanced fill factor. A planar perovskite solar cell with grain boundary and interface passivation achieves a steady-state efficiency of 18.42%.

Lead-free inverted planar formamidinium tin triiodide perovskite solar cells achieving power conversion efficiencies up to 6.22%

Efficient lead (Pb)-free inverted planar formamidinium tin triiodide (FASnI3 ) perovskite solar cells (PVSCs) are demonstrated. Our FASnI3 PVSCs achieved average power conversion efficiencies (PCEs) of 5.41% ± 0.46% and a maximum PCE of 6.22% under forward voltage scan. The PVSCs exhibit small photocurrent-voltage hysteresis and high reproducibility. The champion cell shows a steady-state efficiency of ≈6.00% for over 100 s.

Fabrication of Efficient Low-Bandgap Perovskite Solar Cells by Combining Formamidinium Tin Iodide with Methylammonium Lead Iodide

Mixed tin (Sn)-lead (Pb) perovskites with high Sn content exhibit low bandgaps suitable for fabricating the bottom cell of perovskite-based tandem solar cells. In this work, we report on the fabrication of efficient mixed Sn-Pb perovskite solar cells using precursors combining formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). The best-performing cell fabricated using a (FASnI3)0.6(MAPbI3)0.4 absorber with an absorption edge of ∼1.2 eV achieved a power conversion efficiency (PCE) of 15.08 (15.00)% with an open-circuit voltage of 0.795 (0.799) V, a short-circuit current density of 26.86(26.82) mA/cm(2), and a fill factor of 70.6(70.0)% when measured under forward (reverse) voltage scan. The average PCE of 50 cells we have fabricated is 14.39 ± 0.33%, indicating good reproducibility.

Efficient fully-vacuum-processed perovskite solar cells using copper phthalocyanine as hole selective layers

The state-of-the-art organic–inorganic lead halide perovskite solar cells use organic materials as hole selective layers that are unstable, thermally and chemically, and expensive. Here we demonstrate efficient room-temperature fully-vacuum-processed planar perovskite solar cells using small-molecule organic copper phthalocyanine (CuPc), which has chemical and thermal stability while also being relatively inexpensive, as the hole selective material. The best-performing planar perovskite solar cell using a CuPc hole selective layer achieved a power conversion efficiency of 15.42% with an open circuit voltage of 1.04 V and a fill factor of 77.47%, measured under reverse voltage scanning, and a steady-state efficiency of 14.5%. The cell showed improved stability as compared to reference cells using conventional organic hole selective layers. Our results suggest that thermally evaporated CuPc is an excellent hole selective material for fabricating large-area and low-cost flexible perovskite solar cells with good long-term stability.

Effects of annealing temperature of tin oxide electron selective layers on the performance of perovskite solar cells

Efficient lead halide perovskite solar cells have been realized using SnO2 as electron selective layers (ESLs). Here, we report on the effects of the annealing temperature of solution-processed SnO2 ESLs on the performance of perovskite solar cells. We find that the cells using low-temperature annealed SnO2 (LT-SnO2) ESLs outperform the cells using high-temperature annealed SnO2 (HT-SnO2) ESLs, exhibiting higher open circuit voltages and fill factors. Structural, electrical, optical, and electrochemical characterizations reveal the origin of the performance differences: LT-SnO2 produces better film coverage, wider band gap, and lower electron density than that of HT-SnO2. The confluence of these properties results in more effective transportation of electrons and blocking of holes, leading to lower interface recombination. Therefore, LT-SnO2 ESLs are preferred for manufacturing perovskite solar cells on flexible substrates.

Efficient planar perovskite solar cells using room-temperature vacuum-processed C60 electron selective layers

Efficient organic–inorganic lead halide perovskite solar cells with regular structure typically use solution-processed electron selective layers. Here, we demonstrated efficient planar perovskite solar cells using vacuum-processed C60 compact electron selective layers at room temperature. The best-performing planar perovskite solar cell has shown a power conversion efficiency of 15.14% with an open circuit voltage of 1.08 V and a fill factor of 74.51% measured under reverse voltage scanning. Our results suggest that vacuum-processed fullerene electron selective layer is a good candidate for fabricating all perovskite tandem solar cells.

Improving the Performance of Formamidinium and Cesium Lead Triiodide Perovskite Solar Cells using Lead Thiocyanate Additives

Formamidinium lead triiodide (FAPbI3 ) is considered as an alternative to methylammonium lead triiodide (MAPbI3 ) because of its lower band gap and better thermal stability. However, owing to the large size of FA cations, it is difficult to synthesize high-quality FAPbI3 thin films without the formation of an undesirable yellow phase. Smaller sized cations, such as MA and Cs, have been successfully used to suppress the formation of the yellow phase. Whereas FA and MA lead triiodide perovskite solar cells (PVSCs) have achieved power conversion efficiencies (PCEs) higher than 20 %, the PCEs of formamidinium and cesium lead triiodide (FA1-x Csx PbI3 ) PVSCs have been only approximately 16.5 %. Herein, we report our examination of the main factors limiting the PCEs of (FA1-x Csx PbI3 ) PVSCs. We find that one of the main limiting factors could be the small grain sizes (≈120 nm), which leads to relatively short carrier lifetimes. We further find that adding a small amount of lead thiocyanate [Pb(SCN)2 ] to the precursors can enlarge the grain size of (FA1-x Csx PbI3 ) perovskite thin films and significantly increase carrier lifetimes. As a result, we are able to fabricate (FA1-x Csx PbI3 ) PVSCs with significantly improved open-circuit voltages and fill factors and, therefore, enhanced PCEs. With an optimal 0.5 mol % Pb(SCN)2 additive, the average PCE is increased from 16.18±0.50 (13.45±0.78) % to 18.16±0.54 (16.86±0.63) % for planar FA0.8 Cs0.2 PbI3 PVSCs if measured under reverse (forward) voltage scans. The champion cell registers a PCE of 19.57 (18.12) % if measured under a reverse (forward) voltage scan, which is comparable to that of the best-performing MA-containing planar FA-based lead halide PVSCs.

Low-temperature plasma-enhanced atomic layer deposition of tin oxide electron selective layers for highly efficient planar perovskite solar cells

Recent progress has shown that low-temperature processed tin oxide (SnO2) is an excellent electron selective layer (ESL) material for fabricating highly efficient organic–inorganic metal-halide perovskite solar cells with a planar cell structure. Low-temperature processing and a planar cell structure are desirable characteristics for large-scale device manufacturing due to their associated low costs and processing simplicity. Here, we report that plasma-enhanced atomic layer deposition (PEALD) is able to lower the deposition temperature of SnO2 ESLs to below 100 °C and still achieve high device performance. With C60-self-assembled monolayer passivation, our PEALD SnO2 ESLs deposited at ∼100 °C led to average power conversion efficiencies higher than 18% (maximum of 19.03%) and 15% (maximum of 16.80%) under reverse voltage scan for solar cells fabricated on glass and flexible polymer substrates, respectively. Our results thus demonstrate the potential of the low-temperature PEALD process of SnO2 ESLs for large-scale manufacturing of efficient perovskite solar cells.

Cooperative tin oxide fullerene electron selective layers for high-performance planar perovskite solar cells

Both tin oxide (SnO2) and fullerenes have been reported as electron selective layers (ESLs) for producing efficient lead halide perovskite solar cells. Here, we report that SnO2 and fullerenes can work cooperatively to further boost the performance of perovskite solar cells. We find that fullerenes can be redissolved during perovskite deposition, allowing ultra-thin fullerenes to be retained at the interface and some dissolved fullerenes infiltrate into perovskite grain boundaries. The SnO2 layer blocks holes effectively; whereas, the fullerenes promote electron transfer and passivate both the SnO2/perovskite interface and perovskite grain boundaries. With careful device optimization, the best-performing planar perovskite solar cell using a fullerene passivated SnO2 ESL has achieved a steady-state efficiency of 17.75% and a power conversion efficiency of 19.12% with an open circuit voltage of 1.12 V, a short-circuit current density of 22.61 mA cm−2, and a fill factor of 75.8% when measured under reverse voltage scanning. We find that the partial dissolving of fullerenes during perovskite deposition is the key for fabricating high-performance perovskite solar cells based on metal oxide/fullerene ESLs.

Thermally evaporated methylammonium tin triiodide thin films for lead-free perovskite solar cell fabrication

We report on the synthesis of methylammonium tin triiodide (MASnI3) thin films at room temperature by a hybrid thermal evaporation method and their application in fabricating lead (Pb)-free perovskite solar cells. The as-deposited MASnI3 thin films exhibit smooth surfaces, uniform coverage across the entire substrate, and strong crystallographic preferred orientation along the 〈100〉 direction. By incorporating this film with an inverted planar device architecture, our Pb-free perovskite solar cells are able to achieve an open-circuit voltage (Voc) up to 494 mV. The relatively high Voc is mainly ascribed to the excellent surface coverage, the compact morphology, the good stoichiometry control of the MASnI3 thin films, and the effective passivation of the electron-blocking and hole-blocking layers. Our results demonstrate the potential capability of the hybrid evaporation method to prepare high-quality Pb-free MASnI3 perovskite thin films which can be used to fabricate efficient Pb-free perovskite solar cells.