Michael J. Heben

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 (

Iron Pyrite Nanocrystal Film As A Copper-Free Back Contact For Polycrystalline CdTe Thin Film Solar Cells

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

Environmental analysis of perovskites and other relevant solar cell technologies in a tandem configuration

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.

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

We report the application of thin film nanocrystalline (NC) FeS2 as the copper-free back contact for CdTe solar cells. The FeS2-NC layer is prepared from solution directly on the CdTe surface using drop-casting coupled with a hydrazine treatment at ambient temperature and pressure, and requires no thermal treatment. Copper-free solar cells based on the CdS/CdTe/FeS2-NC/Au architecture exhibit device efficiencies 490% that of a standard Cu/Au back contact devices. The FeS2-NC back contact solar cells show good thermal stability under initial tests. Devices prepared with untreated FeS2-NC back contacts display a strong “S-kink” behavior which we correlate with a high hole-transport barrier arising from inter-NC organic surfactant molecules. & 2015 Elsevier B.V. All rights reserved.

Spray pyrolysis of semi-transparent backwall superstrate CuIn(S,Se) 2 solar cells

Future high performance PV devices are expected to be tandem cells consisting of a low bandgap bottom cell and a high bandgap top cell. In this study, we developed a cradle-to-end of use life cycle assessment model to evaluate the environmental impacts, primary energy demand (PED), and energy payback time (EPBT) of four integrated two-terminal tandem solar cells composed of either Si bottom and lead-based perovskite (PKPb) top cells (Si/PKPb), copper indium gallium selenide (CIGS) and PKPb (CIGS/PKPb), copper zinc tin selenide (CZTS) and PKPb (CZTS/PKPb), or tin-lead based perovskite (PKSn,Pb) and PKPb (PKSn,Pb/PKPb). Environmental impacts from single junction Si solar cells were used as a reference point to interpret the results. We found that the environmental impacts for a 1 m2 area of a cell were largely determined by the bottom cell impacts and ranged from 50% (CZTS/PKPb) to 120% of those of a Si cell. The ITO layer used in Si/PKPb, CZTS/PKPb, and PKSn,Pb/PKPb is the most impactful after the Si and CIGS absorbers, and contributed up to 70% (in PKSn,Pb/PKPb) of the total impacts for these tandem PVs. Manufacturing a single two-terminal device was found to be a more environmentally friendly option than manufacturing two constituent single-junction cells and can reduce the environmental impacts by 30% due to the exclusion of extra glass, encapsulation, front contact and back contact layers. PED analysis indicated that PKSn,Pb/PKPb manufacturing has the least energy-intensive processing, and the EPBTs of Si/PKPb, CIGS/PKPb, CZTS/PKPb, and PKSn,Pb/PKPb tandems were found to be ∼13, ∼7, ∼2, and ∼1 months, respectively. On an impacts per kW h of Si basis the environmental impacts of all the devices were much higher (up to ∼10 times). These results can be attributed to the low photoconversion efficiency (PCE) and short lifetime that were assumed. While PKSn,Pb/PKPb has higher impacts than Si based on current low PCE (21%) and short lifetime (5 years) assumptions, it can outperform Si if its lifetime and PCE reach 16 years and 30%, respectively. Among the configurations considered, the PKSn,Pb/PKPb structure has the potential to be the most environmentally friendly technology.

Semiconducting carbon single-walled nanotubes as a cu-free, barrier-free back contact for CdTe solar cell

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.

A dynamic calibration technique for temperature programmed desorption spectroscopy

We explored the feasibility of depositing CuIn(S,Se)2 (CIS) absorbers using a recently developed hydrazine-based spray pyrolysis method in the backwall superstrate configuration. The devices were fabricated in a novel configuration consisting of a solution-processed CIS/CdS p-n junction sandwiched between two transparent conducting layers and photovoltaic responses was demonstrated with illumination through either side of the device. The structural, compositional, and electrical properties of the devices were investigated. The current voltage characteristics and quantum efficiency of the backwall superstrate and conventional substrate devices were studied. The performance of the backwall superstrate devices was less than that of the control devices due to the relatively thick absorber thickness and high sheet resistance of the transparent back contact. Further improvement in the crystal quality and stoichiometry of CIS deposition should lead to high efficiency devices with thinner and better quality absorbers.

Life cycle toxicity analysis of emerging PV cells

Copper diffusion from the back contact degrades the performance of CdTe solar cells over time and increases the levelized cost of electricity production from CdTe photovoltaics. Recently, carbon single-wall nanotubes (SWNTs) were shown to be a Cu-free, stable alternative that preserves the device efficiency (Phillips et al., Nano Letter, 2013). Large diameter tube samples containing a mixture of semiconducting (s-SWNT) and metallic (m-SWNT) species were used in the previous work, and the mechanisms leading to a low back barrier for majority carrier flow were not clear. The good performance of the back contact was ascribed to the interaction between the s-SWNTs in the film and the polycrystalline facets of the CdTe surfaces. In that case, the s-SWNT species had small bandgaps (~0.6-0.8 eV). Here, in an attempt to develop a more detailed understanding of the SWNT/CdTe back contact, we employed SWNT samples that are predominantly semiconducting (95%) and of larger bandgap (~1.1-1.3 eV). The power conversion efficiency of these unoptimized devices was 11.5 % with a s-SWNT back contact, as compared to 11.2% with a standard Cu/Au back contact.

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

A novel, rapid and accurate calibration procedure as a means for quantitative gas desorption measurement by temperature programmed desorption (TPD) spectroscopy is presented. Quantitative measurement beyond the linear regime of the instrument is achieved by associating an instantaneous calibrated molar flow rate of gas to the detector response. This technique is based on fundamental methods, and is independently verified by comparison to the hydrogen desorption capacity of a known standard metal hydride with known stoichiometry. The TPD calibration procedure described here may be used for any pure gas, and the accuracy is demonstrated for the specific case of hydrogen.