Suneth C. Watthage

Pathways toward high-performance perovskite solar cells: review of recent advances in organo-metal halide perovskites for photovoltaic applications

Abstract. Organo-metal halide perovskite–based solar cells have been the focus of intense research over the past five years, and power conversion efficiencies have rapidly been improved from 3.8 to >21%. This article reviews major advances in perovskite solar cells that have contributed to the recent efficiency enhancements, including the evolution of device architecture, the development of material deposition processes, and the advanced device engineering techniques aiming to improve control over morphology, crystallinity, composition, and the interface properties of the perovskite thin films. The challenges and future directions for perovskite solar cell research and development are also discussed.

A technoeconomic analysis of perovskite solar module manufacturing with low-cost materials and techniques

After rapid progress in the past few years, emerging solar cells based on metal halide perovskites have become a potential candidate to rival and even outperform crystalline silicon photovoltaics (PV) in the marketplace. With high material utilization, easy manufacturing processes, and high power conversion efficiencies >20%, many experts anticipate that perovskite solar cells (PSCs) will be one of the cheapest PV technologies in the future. Here we evaluate the economic potential of PSCs by developing a bottom-up cost model for perovskite PV modules fabricated using feasible low-cost materials and processes. We calculate the direct manufacturing cost (

Enhanced Grain Size, Photoluminescence, and Photoconversion Efficiency with Cadmium Addition during the Two-Step Growth of CH3NH3PbI3

31.7 per m2) and the minimum sustainable price (MSP,

Investigation of degradation mechanisms of perovskite-based photovoltaic devices using laser beam induced current mapping

0.41 per Wp) for a standard perovskite module manufactured in the United States. Such modules, operating at 16% photoconversion efficiency in a 30-year, unsubsidized, utility-level power plant, would produce electricity at levelized cost of energy (LCOE) values ranging from 4.93 to 7.90 ¢ per kW per h. We discuss limitations in comparing calculated MSPs to actual market prices, determine the effect of module lifetime, examine the effects of alternative materials and constructions, and indicate avenues to further reduce the MSP and LCOE values. The analysis shows that PSCs can emerge as a cost leader in PV power generation if critical remaining issues can be resolved.

Spatially resolved characterization of solution processed perovskite solar cells using the LBIC technique

Control over grain size and crystallinity is important for preparation of methylammonium lead iodide (MAPbI3) solar cells. We explore the effects of using small concentrations of Cd2+ and unusually high concentrations of methylammonium iodide during the growth of MAPbI3 in the two-step solution process. In addition to improved crystallinity and an enhancement in the size of the grains, time-resolved photoluminescence measurements indicated a dramatic increase in the carrier lifetime. As a result, devices constructed with the Cd-modified perovskites showed nearly a factor of 2 improvement in the power conversion efficiency (PCE) relative to similar devices prepared without Cd addition. The grains also showed a higher degree of orientation in the ⟨110⟩ direction, indicating a change in the growth mechanism, and the films were compact and smooth. We propose a Cd-modified film growth mechanism that invokes a critical role for low-dimensional Cd perovskites to explain the experimental observations.

Simultaneous shunt protection and back contact formation for CdTe solar cells with single wall carbon nanotube layers

Solution processed thin film photovoltaic devices incorporating organohalide perovskites have progressed rapidly in recent years and achieved energy conversion efficiencies greater than 20%. However, an important issue limiting their commercialization is that device efficiencies often drop within the first few hundred hours of operation. To explore the origin of the device degradation and failure in perovskite solar cells, we investigated the spatial uniformity of current collection at different stages of aging using two-dimensional laser beam induced current (LBIC) mapping. We validated that the local decomposition of the perovskite material is likely due to interactions with moisture in the air by comparing photocurrent collection in perovskite devices that were maintained in different controlled environments. We show that the addition of a poly(methyl methacrylate)/single-wall carbon nanotube (PMMA/SWCNT) encapsulation layer prevents degradation of the device in moist air. This suggests a route toward perovskite solar cells with improved operational stability and moisture resistance.

In-situ observation of moisture-induced degradation of perovskite solar cells using laser-beam induced current

Perovskite organometal halide based solar cells have recently attracted substantial attention due to high power conversion efficiency and ease of processing. Their photovoltaic performance is significantly affected by perovskite film morphology and uniformity regardless of the deposition method. To compare the performance of perovskite solar cells prepared by different solution-based deposition methods and treatments, we used laser beam induced current (LBIC) to spatially resolve the current collection in different devices. Our results show that devices fabricated by the sequential deposition method yield a higher and more uniform LBIC distribution than those prepared by a single-step deposition. The non-uniformity in the LBIC is attributed to microscopic defects and impurity phases in the perovskite films. LBIC imaging provides useful information that will help optimize the growth conditions for better devices.

Investigation on the nucleation and growth mechanisms of perovskite formation in the two-step solution process

Thin film photovoltaic (PV) devices and modules prepared by commercial processes can be severely compromised by through-device low resistance electrical pathways. The defects can be due to thin or missing semiconductor material, metal diffusion along grain boundaries, or areas containing diodes with low turn-on potentials. We report the use of single wall carbon nanotube (SWCNT) layers to enable both protection against these defects and back contact formation for CdTe PV devices. Samples prepared with a SWCNT back contact exhibited good efficiency and did not require shunt protection, while devices prepared without shunt protection using a standard metal back contact performed poorly. We describe the mechanism by which the SWCNT layer functions. In addition to avoiding the need for shunt protection by other means, the SWCNT film also provides a route to higher short circuit currents.

RF-sputtered Cd 2 SnO 4 for flexible glass CdTe solar cells

Solar cells based on organic-inorganic metal halide perovskites have been the focus of photovoltaic research over the past few years due to high power conversion efficiencies up to 22.1% and inexpensive manufacturing costs. However, commercialization of perovskite PV technology is hindered by lack of long-term stability. To elucidate the degradation mechanisms in the state of the art perovskite solar cells, we used laser beam induced current (LBIC) mapping to spatially resolve the device degradation during aging under high humidity conditions. We confirm that perovskites are prone to decomposition in the presence of water. By varying the absorber and hole-transport materials of the devices, we are able to compare performance and identify the water ingress and degradation mechanisms. These results provide insight into the design of materials and device architectures that may improve operational stability of perovskite solar cells.

Evolution of Perovskite Solar Cells

Organic-inorganic hybrid lead halide perovskites have moved to the forefront of photovoltaic research in recent years due to high device efficiency and low-cost preparation methods. Among various deposition methods, the two-step solution process is a widely used route to prepare uniform and conformal perovskite thin films. Here, we investigate the nucleation and growth mechanisms of methylammonium lead iodide perovskite (MAPbL·) formed by reacting pre-deposited PbI2 thin films with different concentrations of methylammonium iodide (MAI) solution. We propose that the formation of the perovskite material is determined by the MAI concentration, and that there are three dominant mechanisms. At MAI concentrations less than 10 mg/mL, Ostwald ripening dominates the perovskite formation. As the MAI concentration is increased from 10 to 20 mg/mL, a dense layer is formed at the top of the PbI2 film that hinders the diffusion of MAI and results in incomplete conversion. Further increase of MAI concentration above 20 mg/mL leads to the formation of low-dimensional perovskites which allow the MAI to diffuse throughout the PbI2 layer. The low-dimensional perovskites can be converted into the appropriate structure with a moderate heat treatment.