Perovskite solar cells (PSCs) have undergone a dramatic increase in laboratory-scale efficiency to more than 25%, which is comparable to Si-based single-junction solar cell efficiency. However, the efficiency of PSCs drops from laboratory-scale to large-scale perovskite solar modules (PSMs) because of the poor quality of perovskite films, and the increased resistance of large-area PSMs obstructs practical PSC applications. An in-depth understanding of the fabricating processes is vital for precisely controlling the quality of large-area perovskite films, and a suitable structural design for PSMs plays an important role in minimizing energy loss. In this review, we discuss several solution-based deposition techniques for large-area perovskite films and the effects of operating conditions on the films. Furthermore, different structural designs for PSMs are presented, including the processing technologies and device architectures.
Lead toxicity in perovskite materials, which have hazardous effects on the environment and the human body, has drawn considerable attention to emerging photovoltaic technology perovskite solar cells. Despite the capability of other strategies to prevent lead leakage, chemisorption is another efficient approach to block Pb leaching by employing Pb absorbents in/out of device structures. This review discusses lead toxicity and summarizes the recent research about chemisorption strategies by their functions: additives, the hole-transporting layers, interfacial modifiers, and encapsulation layers. Finally, the basic guidelines and challenges for designing novel Pb-adsorbing materials and encapsulation structures are presented.
Crystalline silicon (c-Si) heterojunction (HJT) solar cells are one of the promising technologies for next-generation industrial high-efficiency silicon solar cells, and many efforts in transferring this technology to high-volume manufacturing in the photovoltaic (PV) industry are currently ongoing. Metallization is of vital importance to the PV performance and long-term reliability of HJT solar cells. In this review, we summarize the development status of metallization approaches for high-efficiency HJT solar cells. For conventional screen printing technology, to avoid the degradation of the passivation properties of the amorphous silicon layer, a low-temperature-cured (< 250 ℃) paste and process are needed. This process, in turn, leads to high line/contact resistances and high paste costs. To improve the conductivity of electrodes and reduce the metallization cost, multi-busbar, fine-line printing, and low-temperature-cured silver-coated copper pastes have been developed. In addition, several potential metallization technologies for HJT solar cells, such as the Smart Wire Contacting Technology, pattern transfer printing, inkjet/FlexTrailprinting, and copper electroplating, are discussed in detail. Based on the summary, the potential and challenges of these metallization technologies for HJT solar cells are analyzed.
As new-generation solar cells, quantum dot-sensitized solar cells (QDSCs) have the outstanding advantages of low cost and high theoretical efficiency; thus, such cells receive extensive research attention. Their power conversion efficiency (PCE) has increased from 5% to over 15% in the past decade. However, compared with the theoretical efficiency (44%), the PCE of QDSCs still needs further improvement. The low loading amount of quantum dots (QDs) is a key factor limiting the improvement of cell efficiency. The loading amount of QDs on the surface of the substrate film is important for the performance of QDSCs, which directly affects the light-harvesting ability of the device and interfacial charge recombination. The optimization of QD deposition and the improvement of the loading amount are important driving forces for the rapid development of QDSCs in recent years and a key breakthrough in future development. In this paper, the research progress of QD deposition on the surface of substrate films in QDSCs was reviewed. In addition, the main deposition methods and their advantages and disadvantages were discussed, and future research on the further increase in loading amount was proposed.
Cyano substitution is vital to the molecular design of polymer semiconductors toward highly efficient organic solar cells. However, how regioselectivity impacts relevant optoelectronic properties in cyano-substituted bithiophene systems remain poorly understood. Three regioisomeric cyano-functionalized dialkoxybithiophenes BTHH, BTHT, and BTTT with head-to-head, head-to-tail, and tail-to-tail linkage, respectively, were synthesized and characterized in this work. The resulting polymer semiconductors (PBDTBTs) based on these building blocks were prepared accordingly. The regiochemistry and property relationships of PBDTBTs were investigated in detail. The BTHH moiety has a higher torsional barrier than the analogs BTHT and BTTT, and the regiochemistry of dialkoxybithiophenes leads to fine modulation in the optoelectronic properties of these polymers, such as optical absorption, band gap, and energy levels of frontier molecular orbitals. Organic field-effect transistors based on PBDTBTHH had higher hole mobility (4.4 × 10−3 cm2/(V·s)) than those (ca. 10−4 cm2/(V·s)) of the other two polymer analogs. Significantly different short-circuit current densities and fill factors were obtained in polymer solar cells using PBDTBTs as the electron donors. Such difference was probed in greater detail by performing space-charge-limited current mobility, thin-film morphology, and transient photocurrent/photovoltage characterizations. The findings highlight that the BTHH unit is a promising building block for the construction of polymer donors for high-performance organic photovoltaic cells.
The development of new materials plays a critical role in improving the efficiency of organic solar cells (OSCs). At present, the relatively high-lying highest occupied molecular orbital (HOMO) level of the high-efficiency polymer donor is regarded as one of the main reasons for the low open-circuit voltage (V oc). In this work, we introduced the strong electron-withdrawing thiazole unit into the construction of a polymer donor. We designed and prepared an alternating donor–acceptor material, namely PSZ, by copolymerizing 4-methyl thiazole with an electron-donating benzodithiophene unit and studied its application in high-efficiency OSCs. The optical and electrical properties of the new material were characterized by UV–Vis absorption spectroscopy and electrochemical cyclic voltammetry. Results show that PSZ is a typical wide-bandgap material with a high optical bandgap of 2.0 eV and a deep HOMO level of − 5.70 eV. When a non-fullerene BTP-eC9 was selected as the acceptor material, V oc reached 0.88 V in the resulting device, and the corresponding power conversion efficiency (PCE) was 8.15%. In addition, when PSZ was added as the third component to the binary photoactive combination with PBDB-TF as the donor and BTP-eC9 as the acceptor, V oc of the cell device could be increased, thereby obtaining a high PCE of 17.4%. These results indicated that introducing thiazole units into polymer donors can remarkably reduce the HOMO levels and improve V oc and PCE in OSCs.
Fluorine substitution was applied to the donor and acceptor segments of block copolymers to understand the impact of molecular structure on photovoltaic block copolymers and explore efficient materials for single-component organic solar cells (SCOSCs). Along this line, three fluorinated block copolymers, namely PBDB-T-b-PTYF6, PM6-b-PTY6, and PM6-b-PTYF6, derived from PBDB-T-b-PTY6 were designed and synthesized. The UV–Vis absorption, energy level, and thin-film morphology of these block copolymers were systematically characterized. All fluorinated block copolymers show narrow bandgap and improved crystallinity. An enhanced open-circuit voltage was observed in the SCOSC based on PM6-b-PTY6. However, SCOSCs based on all fluorinated block copolymers exhibited low short-circuit current due to energy level mismatch and therefore had low power conversion efficiency at around 4%. By contrast, the SCOSCs based on control block copolymer PBDB-T-b-PTY6 exhibited the highest power conversion efficiency approaching 10%, with a high short-circuit current of 18.57 mA/cm2. Our study was the first to perform fluorination on photovoltaic block copolymers and provides insight into precisely controlling the polymer structure and understanding the structure–property relationship in SCOSCs based on block copolymers.
Ensuring high power conversion efficiency, partially or completely replacing Pt electrodes with inexpensive materials is one of the important development directions of dye-sensitized solar cells (DSSCs). In this work, we have developed a three-component (MWCNTs, carbon black and graphite) carbon (tri-carbon) electrode material for DSSC devices combined with the advantages of high electron transfer kinetics of MWCNTs, plentiful catalytic sites in crystal edges of carbon black and superior electrical conductivity and catalytic activity of graphite. Using a tri-carbon electrode, a Pt electrode, and two N719-sensitized photoanodes, a parallel tandem dye-sensitized solar cells are assembled obtaining a high PCE of 10.26% (V oc = 0.70 V, J sc = 19.99 mA/cm2, FF = 73.33%). It opens up a new avenue for the development of low-cost and high-performance DSSCs.
There is an urgent need to use green non-halogenated solvents to prepare polymer solar cells (PSCs) for industrialization. It is time-consuming but necessary to find a suitable non-halogenated solvent/additive combination for a given donor:acceptor materials system. In this research, we report a non-halogenated binary solvent system toluene/diphenyl ether (DPE) for the PBDTT-DTffBT:PC71BM and PM6:Y6 blending systems that exhibit comparable power conversion efficiency (PCE) to that of devices prepared with halogenated solvents. The nanoscale morphology indicates that blending film processed solely with toluene has poor phase segregation and a rough surface, which hinders charge separation and interfacial contact. Besides, the total absorption spectra revealed significant light-trapping losses in the toluene-processed solar cells, resulting in low photocurrent generation. DPE incorporation addresses these issues and significantly improves the short-circuit current density and fill factor. Moreover, non-halogen solvent-processed devices exhibit high hole mobility and low transporting impedance properties. The present study enriches the families of eco-friendly, high-efficiency PSCs fabricated using non-halogenated solvents.