Zhaoning Song

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 (

Wiring-up carbon single wall nanotubes to polycrystalline inorganic semiconductor thin films: low-barrier, copper-free back contact to CdTe solar cells.

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

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

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.

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

We have discovered that films of carbon single wall nanotubes (SWNTs) make excellent back contacts to CdTe devices without any modification to the CdTe surface. Efficiencies of SWNT-contacted devices are slightly higher than otherwise identical devices formed with standard Au/Cu back contacts. The SWNT layer is thermally stable and easily applied with a spray process, and SWNT-contacted devices show no signs of degradation during accelerated life testing.

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

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.

Cost-effective hole transporting material for stable and efficient perovskite solar cells with fill factors up to 82%

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.

Self-Powered All-Inorganic Perovskite Microcrystal Photodetectors with High Detectivity

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.

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

A new small molecule-based hole selective material (HSM), 4,4′,4′′-(7,7′,7′′-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(2,3-dihydrothieno[3,4-b][1,4]dioxine-7,5-diyl))tris(N,N-bis(4-methoxyphenyl)aniline) (TRUX-E-T), has been developed by a facile synthesis with reduced cost. The highest occupied molecular orbital energy level and lowest unoccupied molecular orbital energy level of TRUX-E-T are −5.10 and −2.50 eV, respectively, making it a suitable HSM for lead iodide perovskite solar cells. TRUX-E-T can be smoothly deposited onto perovskite layers, enabling efficient perovskite solar cells with thin TRUX-E-T layers (∼50 nm), which helps cut the unit cost of the HSL used in PVSCs to approximately one-fortieth (1/40) of 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD). Additionally, TRUX-E-T exhibits hole mobilities as high as 2.47 × 10−4 cm2 V−1 s−1, better than spiro-OMeTAD. As a result, our perovskite solar cells using TRUX-E-T have shown high fill factors up to 82%. The champion cell achieved a maximum power conversion efficiency of 18.35% (16.44%) when measured under reverse (forward) voltage scan under AM1.5 G 100 mW cm−2 illumination. Our un-encapsulated cells exhibited good stability in ambient air, maintaining 96.4% of their initial efficiency of 18.35% after 20 days of storage.

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

Organic-inorganic lead halide perovskite microcrystal (MC) films are attractive candidates for fabricating high-performance large-area self-powered photodetectors (PDs) because of their lower trap state density and higher carrier mobility than their polycrystalline counterparts and more suitability of synthesizing large lateral area films than their single-crystal counterparts. Here, we report on the fabrication of self-powered all-inorganic CsPbBr3 perovskite MC PDs with high detectivity, using a modified solution synthesis method. The MCs are up to about 10 μm in size, and the MC layer is also about 11 μm in thickness. Under 473 nm laser (100 mW) illumination, the CsPbBr3 MC PDs show responsivity values of up to 0.172 A W-1, detectivity values of up to 4.8 × 1012 Jones, on/off ratios of up to 1.3 × 105, and linear dynamic ranges of up to 113 dB. These performances are significantly better than those of PDs based on polycrystalline perovskite thin films and comparable with those of PDs based on perovskite single crystals.