Artificial Intelligence-Based, Wavelet-Aided Prediction of Long-Term Outdoor Performance of Perovskite Solar Cells.

The commercial development of perovskite solar cells (PSCs) has been significantly delayed by the constraint of performing time-consuming degradation studies under real outdoor conditions. These are necessary steps to determine the device lifetime, an area where PSCs traditionally suffer. In this work, we demonstrate that the outdoor degradation behavior of PSCs can be predicted by employing accelerated indoor stability analyses. The prediction was possible using a swift and accurate pipeline of machine learning algorithms and mathematical decompositions. By training the algorithms with different indoor stability data sets, we can determine the most relevant stress factors, thereby shedding light on the outdoor degradation pathways. Our methodology is not specific to PSCs and can be extended to other PV technologies where degradation and its mechanisms are crucial elements of their widespread adoption.

Fused Fluorenylindolenine-Donor-Based Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells.

A series of four unsymmetrical squaraine dyes, XSQ1-4, were synthesized using a fused fluorenylindolenine-based donor unit for dye-sensitized solar cells (DSSCs). The fused structure of fluorenylindolenine helped in moving the absorption toward the near-infrared (NIR) region, and the two sp3-C centers available on this donor were utilized to incorporate out-of-plane alkyl chains in opposite directions to control the dye-dye interactions on the TiO2 surface. High extinction coefficient (ε ≥ 105 M-1 cm-1) for absorbing NIR photons and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels with respect to the conduction band of TiO2 and electrolyte for charge injection and dye regeneration processes, respectively, make these dyes potential sensitizers for DSSCs. Introduction of branched alkyl groups in the π-framework helped in controlling dye aggregation to reduce exciton quenching and assisted in TiO2 surface passivation to avoid the charge recombination process. Furthermore, having a naphthyl group on the indole part of the anchoring group containing segment helped to red-shift the absorption spectrum of dyes 15 nm toward the NIR region (XSQ3-4). Among all of the dyes under investigation, XSQ2 gave the best photovoltaic performance, having a short-circuit current density ( JSC) of 13.99 mA cm-2, open-circuit voltage ( VOC) of 0.66 V, and a fill factor (ff) of 0.71, with a device performance (η) of 6.57%. Electrochemical impedance spectroscopy revealed higher electron lifetime on TiO2 for XSQ2, which helps to avoid the charge recombination process.

Homo- and Heterodimeric Dyes for Dye-Sensitized Solar Cells: Panchromatic Light Absorption and Modulated Open Circuit Potential.

The design of dyes for panchromatic light absorption has attracted much attention in the field of dye-sensitized solar cells (DSSCs). An approach to enhance panchromatic light absorption utilizes mixtures of complementary light-absorbing dyes as well as dyes with specific anchoring groups that facilitate interfacial charge transfer with TiO2 . Dipole-dipole interactions between the dye molecules on the surface broaden the spectrum, which results in decreased DSSC device performance. However, controlled aggregation of dyes results in broadening the spectral profile along with enhanced photocurrent generation. To control the dye-dye interaction, dimeric dyes with different dipole lengths D1 -Dsq , Dsq -Dsq were systematically designed and synthesized. The photophysical and electrochemical properties were evaluated and the EHOMO and ELUMO levels were determined; these energy levels determines the electron injection from ELUMO of the dye to ECB of TiO2 and regeneration of oxidized dye by the electrolyte, respectively. The absorption spectra of Dsq -Dsq , D1 -Dsq were broadened in solution compared to model dye Dsq ; this indicates that the dye-dye interaction is prominent in solution. In D1 -Dsq excitation energy transfer between photoexcited D1 and Dsq was explained by using Förster resonance energy transfer (FRET). The homodimeric dye showed a device performace of 2.8 % (Voc 0.607, Jsc 6.62 mA/cm2 , ff 69.3 %),whereas the heterodimeric dye D1 -Dsq showed a device performance of 3.9 % (Voc 0.652 V, Jsc 8.89 mA/cm2 , ff 68.8 %). The increased photocurrent for D1 -Dsq is due to the panchromatic IPCE response compared to Dsq -Dsq . The increased Voc is due to the effective passivation of the TiO2 surface by the spirolinker, and the effective dipole moment that shifts the conduction band on TiO2 . Hence, the open circuit potential, Voc , for the devices prepared from Dsq , D1 -Dsq and Dsq -Dsq were systematically modulated by controlling the intermolecular π-π and intramolecular dipole-dipole interactions of the dimeric dyes.

Orthogonally Functionalized Donor/Acceptor Homo- and Heterodimeric Dyes for Dye-Sensitized Solar Cells: An Approach to Introduce Panchromaticity and Control the Charge Recombination.

Organic dyes possessing conjugated π-framework forms closely packed monolayers on photoanode in dye-sensitized solar cell (DSSC), because of the limitation to control the orientation and the extend of intermolecular π-π interaction, self-aggregation of dyes leads to reduced cell performance. In this report, a series of homodimeric (D1-D1 and D2-D2) and heterodimeric (D1-D2 and D2-D4) donor/acceptor (D/A) dyes containing spiroBiProDOT π-spacer were designed and synthesized by utilizing Pd-catalyzed direct arylation reaction and correlates the device performance with monomeric dyes (D1 and D2). Both the thiophenes (π-spacer) of spiroBiProDOT were functionalized with same or different donor groups which led to homodimeric and heterodimeric chromophores in a single sensitizer. The homodimeric spiro-dye D1-D1 showed higher power conversion efficiency (PCE), of 7.6% with a Voc and Jsc of 0.672 V and 16.16 mA/cm2, respectively. On the other hand, the monomeric D1 exhibited a PCE of 3.2% (Voc of 0.64 V and Jsc of 7.2 mA/cm2), which is lower by 2.4 fold compared to dimeric analogue. The spiro-unit provides flexibility between the incorporated chromophores to orient on TiO2 due to four sp3-centers, which arrest the molecular motions after chemisorption. This study shows a new molecular approach to incorporate two chromophores in the dimeric dye possessing complementary absorption characteristics toward panchromatic absorption. The attenuated charge recombination at TiO2/Dye/redox couple interface in case of D1-D1, owing to better passivation of TiO2 surface, was elucidated through impedance analysis. The FT-IR spectrum of D1-D1 adsorbed on TiO2 film indicated both the carboxylic units were involved in chemisorption which makes strong coupling between dye and TiO2.

A polymer and graphene layer to increase dye regeneration and suppress back electron transfer in dye sensitized solar cells.

Dye regeneration was improved by using an optimum quantity of graphene, which was dispersed in a polymer that suppresses back electron transfer. Using this approach, DSSCs with an efficiency of 10.4% have been fabricated.

ZnO-ZnS Heterojunctions: A Potential Candidate for Optoelectronics Applications and Mineralization of Endocrine Disruptors in Direct Sunlight.

Simple solution combustion synthesis was adopted to synthesize ZnO-ZnS (ZSx) nanocomposites using zinc nitrate as an oxidant and a mixture of urea and thiourea as a fuel. A large thiourea/urea ratio leads to more ZnS in ZSx with heterojunctions between ZnS and ZnO and throughout the bulk; tunable ZnS crystallite size and textural properties are an added advantage. The amount of ZnS in ZSx can be varied by simply changing the thiourea content. Although ZnO and ZnS are wide band gap semiconductors, ZSx exhibits visible light absorption, at least up to 525 nm. This demonstrates an effective reduction of the optical band gap and substantial changes in its electronic structure. Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and secondary-ion mass spectrometry results show features due to ZnO and ZnS and confirm the composite nature with heterojunctions. The above mentioned observations demonstrate the multifunctional nature of ZSx. Bare ZSx exhibits a promising sunlight-driven photocatalytic activity for complete mineralization of endocrine disruptors such as 2,4-dichlorophenol and endosulphan. ZSx also exhibits photocurrent generation at no applied bias. Dye-sensitized solar cell performance evaluation with ZSx shows up to 4% efficiency and 48% incident photon conversion efficiency. Heterojunctions observed between ZnO and ZnS nanocrystallites in high-resolution transmission electron microscopy suggest the reason for effective separation of electron-hole pairs and their utilization.