Produce Power Conversion Efficiencies Research Articles

Performance evaluation of different designs of back-contact perovskite solar cells

Back-contact design for the architecture of devices is a promising approach to develop high-performance perovskite solar cells. Here, numerical simulation methods are used to investigate device properties of back-contact perovskite solar cells (BC–PSCs) with the quasi-interdigitated, flat-interdigitated, and interdigitated electrode designs. The results highlight the principal differences in the designs of the electrodes and provide an investigation and analysis of the impact of these electrodes on the photovoltaic properties of their BC-PSCs. The effect of the perovskite photoactive layer electronic properties on the performance of BC-PSCs is also investigated. It is revealed that while BC-PSCs with the quasi-interdigitated electrode design can potentially produce power conversion efficiencies (PCEs) well above 25 %, BC-PSCs with the flat-interdigitated and interdigitated electrode designs are more tolerant to electronic imperfections in the perovskite layer and can produce PCEs higher than those in devices with the quasi-interdigitated electrode design. Manufacturing and prospective use of electrodes with the quasi-interdigitated, flat-interdigitated, and interdigitated designs in developing BC-PSCs are discussed from the experimental standpoint.

Water‐Soluble Organic Dyes as Efficient Anode Interlayer Materials for PEDOT:PSS‐Free Inverted Bulk Heterojunction Solar Cells

Solution‐processed inverted organic solar cells (OSCs) generally use poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate (PEDOT:PSS) as hole selective anode interlayer (AIL). However, the acidic nature of PEDOT:PSS considerably accelerates the degradation dynamics of OSCs, which shortens the durability of these low‐cost photovoltaic devices. Small organic molecules are attracting growing interest as alternative AIL materials, but their solubility limited to toxic organic solvents hinders the production of environmentally friendly OSCs. Herein, the first inverted OSCs employing non‐PEDOT:PSS solution‐processed top small organic molecule AILs deposited from aqueous solution are reported. The investigated water‐soluble spirobifluorene (SBF) derivatives 1 and 2 show hole mobility (≈4 × 10−3 cm2 V−1 S−1) higher than PEDOT:PSS. Because of their nonacidic nature, the interlayers formed with derivatives 1 or 2 considerably delay the degradation of the top metal electrode compared to OSCs employing PEDOT:PSS interlayers. The PEDOT:PSS‐free OSC devices with inverted configuration with the water‐soluble SBF derivatives as AIL produce power conversion efficiencies above 5% with PTB7‐Th:ITIC active layers and above 8% with PBDB‐T‐2Cl:Y6 active layers, respectively, with an enhancement up to 28% compared to OSCs employing PEDOT:PSS. These results correspond to the highest reported values for PEDOT:PSS‐free small‐molecule inverted OSCs deposited from an aqueous solution.

Synergistic Effect of N,N-Dimethylformamide and Hydrochloric Acid on the Growth of MAPbI3 Perovskite Films for Solar Cells.

Perovskite solar cells have emerged as a promising next-generation electrical power generating tool. However, imperfections in perovskite films are one of the crucial factors preventing the commercialization of perovskite solar cells. Passivation has proven to be an effective strategy to reduce the density of defect states in perovskite crystals and inhibit ion migration. Although significant work on chloride ion and N,N-dimethylformamide (DMF) has shown that the additives are able to passivate different types of trap defects, systematic studies on the effects of DMF and HCl on perovskite crystallization when used in conjunction with each other are elusive. Here, we systematically investigated the synergistic effect of DMF and hydrochloric acid (HCl) on methylammonium (MA+)-based perovskite films with the two-step spin-coating method. As a Lewis base, DMF coordinates well with Pb2+ to facilitate a decrease in the number of defects, thereby improving the carrier separation and transport, while HCl improves the overall perovskite film morphology. Addition of 20 μL HCl/20 μL DMF to 10 mL of methylammonium iodide/isopropyl alcohol solution afforded ca. 500 nm thick perovskite films with no observable defects within the grains. The process allowed fabrication of devices with an active area of 0.16 cm2, which produced power conversion efficiencies up to 18.37% with minimal hysteresis.

Performance optimization of back-contact perovskite solar cells with quasi-interdigitated electrodes

A numerical simulation method is used to investigate intricacies of a complex relation between the back-contact electrode (BCE) geometric parameters, the perovskite photo-absorber layer electronic properties, and device performance in back-contact perovskite solar cells (BC-PSCs) with quasi-interdigitated electrodes (QIDEs). To unlock the full potential of BC-PSC with QIDEs, the device performance was investigated by systematically varying the geometric parameters of BCE and the perovskite photo-absorber layer electronic parameters in order to determine the conditions for a best device performance. BC-PSC with QIDEs have a potential to produce power conversion efficiencies (PCEs) higher than PSCs with the conventional sandwich architecture if optimized parameters for electrode geometry and perovskite electronic properties are used. The findings of the present work give an insight into the work principle of these devices and provide a theoretical guidance for design and fabrication of high-performance BC-PSC with QIDEs.

High-Throughput Screening of Antisolvents for the Deposition of High-Quality Perovskite Thin Films.

One-step solution deposition of high-quality perovskite thin films relies heavily on a small number of antisolvents. Here, we design a simple minimum volume colorimetric solution assay to screen over 100 different solvents. We correctly identify 14 previously reported antisolvents and predict 20 novel candidates. We then refine the assay through analysis of screening results, available solvent properties, and qualitative evaluation of films cast using 50 candidates. Using the refined findings, we successfully demonstrated 15 different antisolvents for characterization and evaluation in inverted devices, including six previously unreported candidates. All candidates produced power conversion efficiencies comparable to chlorobenzene controls without any additional optimization. This work presents the largest scope of antisolvents reported, can be easily adapted to other perovskites, and opens the door to selecting antisolvents based on a wide range of desirable properties including efficiency, usability, safety, and industrial viability.

(Invited) Metal Halide Perovskites at the Nanoscale: High Quality Optoelectronic Materials with Unique Phase Properties

The newly rediscovered perovskite semiconductor system has the potential to be extremely transformative for all optoelectronic devices, especially photovoltaics (PVs). Perovskite semiconductors of the form APbI3 where A is a large +1 charged cation, typically Cs, methylammonium, or formamidinium have had a huge resurgence among materials scientists for outstanding PV properties despite being overlooked for decades. Semiconductors containing the latter two A-site cations listed are hybrid organic-inorganic materials, and as such, are far less understood compared to conventional all inorganic or even organic material systems. Regardless of this spotty formal understanding, lead-halide perovskites have very rapidly been optimized to power conversion efficiency levels on par with all other materials even with extensive history of research. Perovskites show a unique tolerance to crystalline defects that cause trouble in most other semiconductors. Therefore the potential offered is that very high efficiency PVs can be fabricated in extremely fast and inexpensive ways, thus offering a revolution for the solar industry and a direct route toward producing the world’s energy with a simple and clean technology. Long-term durability of the devices is the critical remaining challenge to be solved.1 Two examples of major instabilities in device performance are the volatility of the organic cation and the specific crystal habit in which the material embodies. Nanoscale versions (often termed quantum dots (QDs)) of the all-inorganic metal halide perovskite (CsPbI3) tend to retain the desired perovskite phase due to strain effects at the surface of the QDs whereas conventional films of the same material “relax” to an orthorhombic non-perovskite structure at room temperature. Therefore these QDs potentially solve both of the instability issues. The cubic CsPbI3 QD cells operate with a rather remarkable open-circuit voltage of >1.2 volts and have produced power conversion efficiencies over 13%.2,3 This customizable new nanomaterial system has incredible potential for many applications in optoelectronics, including photovoltaics, LEDs, displays and lasers. We describe the formation of perovskite phase-CsPbI3 QD films with long range electronic transport that retain the high temperature phase in ambient conditions making up the active layer in optoelectronic devices. Perspectives on how this technology can become transformative will be discussed. References A. Christians, P. Schulz, J.S. Tinkham, T.H. Schloemer, S.P. Harvey, B.J .Tremolet de Villers, A. Sellinger, J.J. Berry, J.M. Luther, Nature Energy, 2018, 3 (1), 68.Swarnkar, A.R. Marshall, E.M. Sanehira, B.D. Chernomordik, D.T. Moore, J.A. Christians, T. Chakrabarti, J.M. Luther, Science, 2016, 354 (6308), 92-95.M. Sanehira, A.R. Marshall, J.A. Christians, S.P. Harvey, P.N. Ciesielski, L.M. Wheeler, P. Schulz, L.Y. Lin, M.C. Beard, J.M. Luther, Science Advances, 2017, 3 (10), eaao4204.

Achieving High Efficiency in Solution-Processed Perovskite Solar Cells Using C60/C70 Mixed Fullerenes.

Fullerenes have attracted considerable interest as an electron-transporting layer in perovskite solar cells. Fullerene-based perovskite solar cells produce no hysteresis and do not require high-temperature annealing. However, high power conversion efficiency has been only achieved when the fullerene layer is thermally evaporated, which is an expensive process. In this work, the limitations of a solution-processed fullerene layer have been identified as high crystallinity and the presence of remnant solvents, in contrast to a thermally deposited C60 film, which has low crystallinity and no remaining solvents. As a solution to these problems, a mixed C60 and C70 solution-processed film, which exhibits low crystallinity, is proposed as an electron-transporting layer. The mixed-fullerene-based devices produce power conversion efficiencies as high as that of the thermally evaporated C60-based device (16.7%) owing to improved fill factor and open-circuit voltage. In addition, by vacuum-drying the mixed fullerene film, the power conversion efficiency of the solution-processed perovskite solar cells is further improved to 18.0%. This improvement originates from the enhanced transmittance and charge transport by removing the solvent effect. This simple and low-cost method can be easily used in any type of solar cells with fullerene as the electron-transporting layer.

Inverted Organic Solar Cells Fabricated with Room‐Temperature‐deposited Transparent Multilayer Electrodes

We investigated the electrical, optical, and structural properties of Al‐doped ZnO (AZO)/Ag/AZO and indium gallium zinc oxide (IGZO)/Ag/IGZO multilayer films, and the performance of inverted organic solar cells (OSCs) fabricated with Sn‐doped indium oxide (ITO), AZO/Ag/AZO, and IGZO/Ag/IGZO electrodes. Even though deposited at room temperature, AZO/Ag/AZO (36 nm/19 nm/36 nm) and IGZO/Ag/IGZO (39 nm/19 nm/39 nm) multilayer films showed sheet resistances of 4.1 and 4.2 Ω/sq, resistivities of 3.3 × 10−5 and 4.1 × 10−5 Ω cm, and transmittances of 93 and 88% at 550 nm, respectively. Figures of merit (FOMs) were obtained to be 99.9 and 49.9 × 10−3 Ω−1 for the AZO/Ag/AZO and IGZO/Ag/IGZO films, respectively. Inverted OSCs fabricated using the as‐deposited AZO/Ag/AZO and IGZO/Ag/IGZO electrodes produced power conversion efficiencies (PCEs) of 2.4 and 2.6%, respectively, while that with high‐temperature annealed ITO electrode gave a PCE of 3.2%.

Molecular design and theoretical investigation on the thieno[3,2-b]thienobis(silolothiophene)-based low band gap donor polymers for efficient polymer solar cell

Donor–acceptor (D–A) copolymers have been proved to be excellent candidates for efficient polymer solar cells. In this paper, a series of D–A polymers with the same donor unit of Si4T and different acceptor units are theoretically designed. Two novel strategies (extending the length of π-conjugation and using the electron-deficient groups) have been considered for the conjugated polymer design. The energy levels and band gaps are theoretically investigated using the confirmed density functional theory/time-dependent density functional theory method. The results show that, compared with two original polymers, the newly designed D–A polymers have better predicted performances with smaller band gaps and lower highest occupied molecular orbital energy levels. When combined with fullerene derivatives (PCBM) for organic solar cells, these polymers can produce power conversion efficiencies as high as ∼10%, estimated by Scharber diagrams.

Superior Catalytic Activity of Sub‐5 μm‐Thick Pt/SiC Films as Counter Electrodes for Dye‐Sensitized Solar Cells

AbstractDye‐sensitized solar cells with sub‐5 μm‐thick Pt/SiC‐P (1.79 at. % Pt), Pt/SiC‐M (0.45 at. % Pt), and Pt/SiC‐R (0.39 at. % Pt) counter electrode (CE) films fabricated by using three different processes produced power conversion efficiencies of 6.82, 7.64, and 7.04 % that reached 86.5, 97.0, and 89.3 %, respectively, of the level obtained by using a print‐Pt CE (7.88 %). These materials can reduce the cost of CEs and solve challenges involving Pt.

Synthesis and characterization of diselenenoquinoxaline-based donor–acceptor polymers for organic photovoltaic cells

Two new conjugated polymers, PQSS and PQST, were designed and synthesized; these polymers had alkylselenophene-substituted quinoxaline backbones with selenophene and thiophene, respectively, as electron-donating units. The copolymers showed good solubility and film forming abilities, combined with good thermal stability. The number-average molecular weights (Mn) of PQSS and PQST, determined using gel permeation chromatography (GPC) with a polystyrene standard, were found to be 20,900 (Mw/Mn=1.71) and 22,100 (Mw/Mn=2.41), respectively. The UV–visible absorption maxima of PQSS and PQST were at 617 and 601nm in solution, and at 682 and 668nm in the film state. The PQSS and PQST showed low band gaps of 1.50 and 1.52eV, respectively. Solution-processed field-effect transistors fabricated from these polymers had p-type organic thin film transistor characteristics. The field-effect mobilities of PQSS and PQST were measured to be 1.4×10−4 and 4.8×10−5cm2V−1s−1, respectively. The polymers were combined with a PC71BM ([6,6]-phenyl C71-butyric acid methyl ester) acceptor to fabricate bulk heterojunction solar cells, which produced power conversion efficiencies of 0.40–1.07% under AM 1.5G (100mW/cm2) conditions.

Fullerene-Dependent Miscibility in the Silole-Containing Copolymer PSBTBT-08

A high fullerene molecular miscibility of over 40 wt % is found in the copolymer poly((4,4-octyldithieno(3,2-b:2′,3′-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT-08)—a member of the PSBTBT low-bandgap polymer family that have produced power conversion efficiencies as high as 5.9% in solar cells. This observation suggests molecular miscibility plays a key role in the photovoltaic effect in this system. The level of miscibility is additionally measured to be highly dependent on the fullerene species with significant differences between C60- and C70-based fullerenes, highlighting a new parameter to be monitored and controlled when considering different fullerene moieties and species in organic solar cells. Surprisingly, a wide-angle X-ray scattering study reveals no significant crystallinity in the PSBTBT with octyl side chains, potentially the cause of low mobilities and in stark contrast to dodecyl and ethylhexyl PSBTBTs, which demonstrates the importance of the side chain in device morphology and performance.

3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics

We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.