Ligang Yuan

In this work, high-efficiency nonfullerene polymer solar cells (PSCs) are developed based on a thiazolothiazole-containing wide bandgap polymer PTZ1 as donor and a planar IDT-based narrow bandgap small molecule with four side chains (IDIC) as acceptor. Through thermal annealing treatment, a power conversion efficiency (PCE) of up to 11.5% with an open circuit voltage (V_oc) of 0.92 V, a short-circuit current density (J_sc) of 16.4 mA cm⁻², and a fill factor of 76.2% is achieved. Furthermore, the PSCs based on PTZ1:IDIC still exhibit a relatively high PCE of 9.6% with the active layer thickness of 210 nm and a superior PCE of 10.5% with the device area of up to 0.81 cm². These results indicate that PTZ1 is a promising polymer donor material for highly efficient fullerene-free PSCs and large-scale devices fabrication.

The nonfullerene polymer solar cells based on a wide-bandgap polymer PTZ1 and a narrow-bandgap acceptor IDIC exhibit weak active-layer thickness and area dependence with an optimal power conversion efficiency of 11.5%, indicating that the blend of PTZ1/IDIC has potential for the practical application of polymer solar cells.

Side group of ITIC-like small molecular acceptor (SMA) plays a critical role in crystallization property. In this article, two new SMAs with n-hexylthienyl and n-hexylselenophenyl as side chain, namely ITCPTC-Th and ITCPTC-Se, are designed and synthesized by employing newly developed thiophene-fused ending group (CPTCN). And thiophene and selenophene side group substituted effects of SMA-based fullerene-free polymer solar cells (PSCs) are investigated. A stronger σ-inductive effect between selenophene side group and electron-donating backbone endows ITCPTC-Se with better optical absorption and higher LUMO level, ITCPTC-Th-based PSCs deliver a higher power conversion efficiency of 10.61%. Charge transport and collection, recombination loss mechanism, and morphology of blend films are intensively studied. These results confirm that side group substituted effects of SMAs are multiple and thiophene is a superior option to selenophene as aromatic side group of ITIC-like SMAs.

Two new small molecular acceptors (SMAs), ITCPTC-Th and ITCPTC-Se, are designed and synthesized to investigate thiophene and selenophene side group substituted effects. A polymer solar cell (PSC) based on ITCPTC-Th achieves high power conversion efficiency (PCE) of 10.61%, which are significantly higher than that of ITCPTC-Se-based PSC. This confirms that thiophene is superior to selenophene as side group of ITIC-like SMAs.

Perovskite-based optoelectronic devices have shown remarkable performances, especially in the field of photovoltaics. Still, a rapid solution-processing approach able to produce localized stable perovskite crystals remains a general challenge, and is a key step toward the miniaturization of such materials in on-chip components. This study presents the confined growth of methylammonium (MA) lead halide perovskite crystals that is thermally induced through localized laser irradiation. Importantly, such structures remain stable over time; that is, they neither dissolve back into the surrounding liquid nor detach from the substrate. This is attributed to a chemical reaction locally triggered by the induced heat on the substrate surface that is transferred to the perovskite precursors (liquid) layer, thus generating “on-demand” MA ions from the N-methylformamide solvent. By tuning the laser parameters, such as power density or irradiation time, variations in shape and size of the crystals, from microcrystals of ≈50 µm to nanocuboids of ≈500 nm, are observed. This study also demonstrates that with an optimized distance between the irradiated regions and by controlling the relative laser displacement speed, luminescent and photoconductive MAPbBr₃ wires and microplates can be generated.

Stable MAPbBr₃ crystals with different sizes are successfully localized on a flat substrate via laser-induced heating of the liquid precursors. By adjusting the infrared laser parameters, luminescent arrays and photoconductive wires are grown on-site. This technique can be used to guide the writing of other patterns for specific functionalities.

Organic–inorganic hybrid halide perovskite solar cells (PSCs) have recently drawn enormous attentions due to their impressive performance (>22%) and low temperature solution processability (<150 °C). Current solution process involves application of a large amount of toxic solvents, such as chlorobenzene, which is heavily employed in both the perovskite layer and the hole transport layer (HTL) deposition. Herein, this study employs green solvent of ethyl acetate for engineering efficient perovskite and HTL layers, which enables a synergic interface (perovskite/HTL) optimization. A champion efficiency of 19.43% is obtained for small cells (0.16 cm² with mask) and over 14% for large size modules (5 × 5 cm²). The PSCs prepared from the green solvent engineering demonstrate superior performance on both efficiency and stability over their chlorobenzene counterparts. These enhancements are ascribed to the in situ inhibition on carrier recombination induced by interfacial defects during the solution processing, which enables about 2/3 reduction of calculated recombination rate. Thus, the green solvent route shows the great potential toward environmental-friendly manufacturing.

The widely used toxic chlorobenzene for the perovskite and Spiro-OMeTAD film processing is replaced by a green solvent of ethyl acetate. This green solvent engineering produces pinhole-free films of both the perovskite and Spiro-OMeTAD hole transport layer. Via the synergic interface optimization, an impressive power conversion efficiency up to 19.43% is achieved.

A high power conversion efficiency of 6.9% from all-polymer solar cells with polymers as both donor and acceptor is achieved with good stability over 60 days as reported by Xiaofeng Xu, René A. J. Janssen, Ergang Wang, and co-workers in article number 1602722. The random copolymer PNDI-T10 could be a promising alterative acceptor to the widely used alternating polymers PNDI-T and N2200, as it delivers better performance in the resulting solar cells.

A new strategy for designing ternary solar cells is reported in this paper. A low-bandgap polymer named PTB7-Th and a high-bandgap polymer named PBDTTS-FTAZ sharing the same bulk ionization potential and interface positive integer charge transfer energy while featuring complementary absorption spectra are selected. They are used to fabricate efficient ternary solar cells, where the hole can be transported freely between the two donor polymers and collected by the electrode as in one broadband low bandgap polymer. Furthermore, the fullerene acceptor is chosen so that the energy of the positive integer charge transfer state of the two donor polymers is equal to the energy of negative integer charge transfer state of the fullerene, enabling enhanced dissociation of all polymer donor and fullerene acceptor excitons and suppressed bimolecular and trap assistant recombination. The two donor polymers feature good miscibility and energy transfer from high-bandgap polymer of PBDTTS-FTAZ to low-bandgap polymer of PTB7-Th, which contribute to enhanced performance of the ternary solar cell.

Ternary solar cells with minimum voltage losses around 0.25 eV are designed by combining two donor polymers with same bulk and interface energy which make the hole transportation like in one donor polymer. The voltage losses were minimized due to E_ICT+ ≈ E_ICT−, where the trade-off between enhancing of charge generation and charge recombination by ICT states arrives at sweet spot.

Fullerene-free OSCs employing n-type small molecules or polymers as the acceptors have recently experienced a rapid rise with efficiencies exceeding 12%. Owing to the good optoelectronic and morphological tunabilities, non-fullerene acceptors exhibit great potential for realizing high-performance and practical OSCs. In this Review, recent exciting progress made in developing highly efficient non-fullerene acceptors is summarized, mainly correlating factors like absorption, energy loss and morphology of new materials to their correspondent photovoltaic performance.

Fullerene-free organic solar cells (OSCs) have made great progress in recent years with efficiencies surpassing 12%. In this Review, recent high-performance non-fullerene acceptors developed for OSCs are summarized, mainly correlating factors like absorption, energy loss and morphology of new materials to their correspondent photovoltaic performance. The perspectives for fullerene-free OSCs with efficiency of 15% are briefly discussed.

Despite rapid advances in the field of nonfullerene polymer solar cells (NF-PSCs), successful examples of random polymer-based NF-PSCs are limited. In this study, it is demonstrated that random donor polymers based on thieno[2′,3′:5′,6′]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione (TPTI) containing two simple thiophene (T) and bithiophene (2T) electron-rich moieties (PTTI-Tx) can be promising materials for the fabrication of highly efficient NF-PSCs. With negligible influence on optical bandgaps and energy levels, the crystalline behavior of PTTI-Tx polymers was modulated by varying the T:2T ratio in the polymer backbone; this resulted in the formation of different microstructures upon blending with a nonfullerene m-ITIC acceptor in NF-PSCs. In particular, a PTPTI-T70:m-ITIC system enabled favorable small-scale phase separation with an increased population of face-on oriented crystallites, thereby boosting the processes of effective exciton dissociation and charge transport in the device. Consequently, the highest power conversion efficiency of 11.02% with an enhanced short-circuit current density of 17.12 mA cm⁻² is achieved for the random polymer-based NF-PSCs thus far. These results indicate that random terpolymerization is a simple and practical approach for the optimization of a donor polymer toward highly efficient NF-PSCs.

Over 11% efficiency random polymer-based nonfullerene solar cell is realized on the donor family of PTPTI-Tx containing various thiophene/bithiophene ratios in the backbone. A small-scale phase separation with an increased fraction of face-on oriented crystallites observed in the PTPTI-T70:m-ITIC blend enables efficient exciton dissociation and charge transport, thereby inducing a remarkably enhanced J_SC of 17.12 mA cm⁻² through this system.