Changjian Song

High-Performance Polymer Solar Cells with PCE of 10.42% via Al-Doped ZnO Cathode Interlayer

High-performance polymer solar cells incorporating a low-temperature-processed aluminum-doped zinc oxide (AZO) cathode interlayer are constructed with power conversion efficiency (PCE) of 10.42% based on PTB7-Th:PC71 BM blends (insensitive to the AZO thickness). Moreover, flexible devices on poly(ethylene terephthalate)/indium tin oxide substrates with PCE of 8.93% are also obtained, and welldistributed efficiency and good device stability are demonstrated as well.

Realizing Highly Efficient Inverted Photovoltaic Cells by Combination of Nonconjugated Small-Molecule Zwitterions with Polyethylene Glycol

Organic ionic materials have been reported to be efficient cathode interlayer (CIL) materials in polymer solar cells (PSCs); however, most of them are employed in conventional PSCs. For an inverted structural device which has better stability, the efficiency is still far from expectation and the report is also limited. In this study, by using nonconjugated zwitterions as the CIL and inverted structure, the power conversion efficiency (PCE) is ∼6%, though the PCE can reach 9.14% in the conventional device. By introducing polyethylene glycol (PEG) into the zwitterions, the PCE of the inverted PSCs was improved ∼33% and reached ∼8% mainly because of the enhancement of the open-circuit voltage (Voc) and fill factor (FF). Further research on the device parameters, work functions, morphology of indium tin oxide (ITO) with various CILs, and recombination resistance of the devices indicated that PEG + zwitterion induced not only a lower work function of ITO but also a more uniform morphology of CILs with less contact of the photoactive layer with ITO, which induced suppressed charge recombination and a higher Voc and FF. Enhanced ability in interface modification of PEG + zwitterion CILs displayed a simple and feasible approach to elevate the performance of inverted PSCs with ionic CILs.

Sulfonate anionic small molecule as a cathode interfacial material for highly efficient polymer solar cells

The cathode interlayer is essential to bulk heterojunction polymer solar cells (PSCs). As we all know, most of the organic interfacial materials are amino derivatives, including neutral amine derivatives and ammonium derivatives. Herein, a non-amino small molecule, TBT-a, with sulfonate anionic pendants was synthesized and interface modification was investigated. The PSC with TBT-a as the cathode interlayer exhibited a high power conversion efficiency of 8.68%. We found that the TBT-a interlayer simultaneously enhanced all the device parameters, probably by inducing an effective interface dipole, altering the optical distribution, and enhancing the electron mobility. These results indicated that sulfonate interfacial materials could play a similar role as amine-based interfacial materials in interface modification.

A benzobis(thiadiazole)-based small molecule as a solution-processing electron extraction material in planar perovskite solar cells

A novel small-molecule, B2F, which is based on benzobis(thiadiazole), was designed and synthesized as an electron extraction material for perovskite solar cells (PSCs). Because of the high electron affinity of the benzobis(thiadiazole) unit and the Pb–S bonding, B2F exhibited good adhesion on the perovskite surface and an efficient photoluminescence quenching to CH3NH3PbI3. The simple device with B2F as the solution-processing electron extraction layer without any extra interface layer exhibited an optimal power-conversion efficiency (PCE) of 12.35%. The B2F-based device can be further improved by the addition of C60/BCP as efficient electron transport and hole-blocking layers to enhance electron transport and prevent carrier leakage. A champion PCE of 17.18% was achieved with an open-circuit voltage of 1.052 V, a short-circuit current density of 20.63 mA cm−2 and a fill factor of 79.15%. In summary, we developed an efficient electron extraction material for PSCs, which represents a new building block for the design and development of highly efficient electron transport materials for PSCs in the future.

Recent Advance in Solution‐Processed Organic Interlayers for High‐Performance Planar Perovskite Solar Cells

Abstract Planar heterojunction perovskite solar cells (PSCs) provide great potential for fabricating high‐efficiency, low‐cost, large‐area, and flexible photovoltaic devices. In planar PSCs, a perovskite absorber is sandwiched between hole and electron transport materials. The charge‐transporting interlayers play an important role in enhancing charge extraction, transport, and collection. Organic interlayers including small molecules and polymers offer great advantages for their tunable chemical/electronic structures and low‐temperature solution processibility. Here, recent progress of organic interlayers in planar heterojunction PSCs is discussed, and the effect of chemical structures on device performance is also illuminated. Finally, the main challenges in developing planar heterojunction PSCs based on organic interlayers are identified, and strategies for enhancing the device performance are also proposed.

Perylene Diimide-Based Zwitterion as the Cathode Interlayer for High-Performance Nonfullerene Polymer Solar Cells

Nonfullerene polymer solar cells (PSCs) have earned widespread and intense interest on account of their properties such as tunable energy levels, potential for low-cost production processes, reduced energy losses, and strong light absorption coefficients. Here, a water-/alcohol-soluble zwitterion perylene diimide zwitterion (PDI-z) consisted of sulfobetaine ion as a terminal substituent and PDI as a conjugated core was synthesized. PDI-z was employed as an electron-transport layer (ETL) for nonfullerene PSC devices, obtaining an optimal power conversion efficiency (PCE) above 11.23%. Moreover, nonfullerene PSCs with the PDI-z cathode interlayer displayed an excellent performance on a large scale of interlayer thickness, which was compatible with printing fabrication techniques. Additionally, the PDI-z interlayer presented good ability of modifying high work function metals (for instance, Au, Cu, and Ag) in nonfullerene devices, and the Ag device displayed a PCE of 9.38%. This work provides a good alternative ETL for high-efficiency nonfullerene PSCs.

Carboxylic ester-terminated fulleropyrrolidine as an efficient electron transport material for inverted perovskite solar cells

The interfacial contacts between perovskite crystals and metal electrodes play a significant role in efficient charge transfer in perovskite solar cells (PSCs). In this work, C60 pyrrolidine tris-acid ethyl ester (CPTA-E) has been employed to form a uniform electron transport layer (ETL) covering the perovskite surface in p-i-n-structured PSCs to replace the traditional (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) ETL. X-ray photoelectron spectroscopy analysis of the perovskite/CPTA-E interface reveals that there are strong coordination interactions between the perovskite and CPTA-E, which are beneficial for the adhesion of the CPTA-E ETL on the perovskite surface. On the other hand, steady-state photoluminescence and time-resolved photoluminescence studies of the perovskite films with different quenching layers confirm that CPTA-E ETL has a preferable charge quenching effect compared to the PCBM ETL, which suggests that the CPTA-E ETL has a superior electron extraction and transport ability. The corresponding CPTA-E ETL-based device exhibits a champion power conversion efficiency (PCE) of 17.44% with less hysteresis. Moreover, the steady-state photocurrent output of the CPTA-E-containing PSC is prolonged compared to that of the PCBM-based device. Therefore, this work provides a viable strategy to design suitable electron transport materials for high-performance PSCs.