ZiQi Sun

Reduced graphene oxide (rGO) is added in the [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) electron transport layer (ETL) of planar inverted perovskite solar cells (PSCs), resulting in a power conversion efficiency (PCE) improvement of ≈12%, with a hysteresis-free PCE of 14.5%, compared to 12.9% for the pristine PCBM based device. The universality of the method is demonstrated in PSCs based on CH₃NH₃PbI_3−xCl_x and CH₃NH₃PbI₃ perovskites, deposited through one step and two step spin coating process, respectively. After a comprehensive spectroscopic characterization of both devices, it is clear that the introduction of rGO in PCBM ETL results in an important increase of the ETL conductivity, together with reduced series resistance and surface roughness. As a result, a significant photoluminescence quenching of such perovskite/ETL is observed, confirming the increased measured short circuit current density. Transient absorption measurements reveal that in the rGO-based device, the relaxation process of the excited electrons is significantly faster compared to the reference, which implies that the charge injection rate is significantly faster for the first. Furthermore, the light soaking effect is significantly reduced. Finally, aging measurements reveal that the rGO stabilizes the ELT/perovskite interface, which results in the stabilization of perovskite crystal structure after prolonged illumination.

Planar inverted perovskite solar cells with high efficiency and ambient stability are fabricated based on a reduced graphene oxide (rGO) doped [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) electron transporting layer (ETL). The performance improvement is attributed to enhanced electron extraction, while the enhancement in the lifetime is due to the stabilization of the perovskite/ETL interface of the rGO doped device compared to the pristine.

Efficient monolithic perovskite/perovskite tandem solar cells are fabricated using two perovskite absorbers with complementary bandgaps. By employing doped organic semiconductors, an efficient and selective extraction of the charge carriers is ensured. This study demonstrates perovskite/perovskite tandem cells delivering a maximum efficiency of 18%, highlighting the potential of vacuum-deposited multilayer structures in overcoming the efficiency of single-junction perovskite devices.

Conjugated polymer semiconductors P1 and P2 with bithienopyrroledione (bi-TPD) as acceptor unit are synthesized. Their transistor and photovoltaic performances are investigated. Both polymers display high and balanced ambipolar transport behaviors in thin-film transistors. P1-based devices show an electron mobility of 1.02 cm² V⁻¹ s⁻¹ and a hole mobility of 0.33 cm² V⁻¹ s⁻¹, one of the highest performance reported for ambipolar polymer transistors. The electron and hole mobilities of P2 transistors are 0.36 and 0.16 cm² V⁻¹ s⁻¹, respectively. The solar cells with PC₇₁BM as the electron acceptor and P1/P2 as the donor exhibit a high V_oc about 1.0 V, and a power conversion efficiency of 6.46% is observed for P1-based devices without any additives and/or post treatment. The high performance of P1 and P2 is attributed to their crystalline films and short π–π stacking distance (<3.5 Å). These results demonstrate (1) bi-TPD is an excellent versatile electron-deficient unit for polymer semiconductors and (2) bi-TPD-based polymer semiconductors have potential applications in organic transistors and organic solar cells.

Versatile polymer semiconductors containing bithienopyrroledione unit are designed and synthesized. They exhibit balanced ambipolar transport behaviors with an electron mobility of 1.02 cm² V⁻¹ s⁻¹ and a hole mobility of 0.33 cm² V⁻¹ s⁻¹ in thin-film transistors, and photovoltaic properties with a power conversion efficiency of 6.46% and a high V_oc of 1.02 V in polymer solar cells.

The third generation of photovoltaic technology aims to reduce the fabrication cost and improve the power conversion efficiency (PCE) of solar cells. Singlet fission (SF), an efficient multiple exciton generation (MEG) process in organic semiconductors, is one promising way to surpass the Shockley-Queisser limit of conventional single-junction solar cells. Traditionally, this MEG process has been observed as an intermolecular process in organic materials. The implementation of intermolecular SF in photovoltaic devices has achieved an external quantum efficiency of over 100% and demonstrated significant promise for boosting the PCE of third generation solar cells. More recently, efficient intramolecular SF has been reported. Intramolecular SF materials are modular and have the potential to overcome certain design constraints that intermolecular SF materials possess, which may allow for more facile integration into devices.

Singlet fission (SF), a multiple exciton generation process in organic semiconductors, is one promising way to overcome the Shockley–Queisser limit for the power conversion efficiency (PCE) of photovoltaic solar cells. Recent achievements in engineering intermolecular SF-based photovoltaic devices and prospects of recently developed intramolecular SF materials as active layers in future devices are highlighted.

The efficiency of perovskite optoelectronic devices is increased by a novel method; its suitability for perovskite solar cells, light-emitting diodes, and optical amplifiers is demonstrated. The method is based on the introduction of organic additives during the anti-solvent step in the perovskite thin-film deposition process. Additives passivate grain boundaries reducing non-radiative recombination. The method can be easily extended to other additives.

Continuous and scalable nanopatterning over flexible substrates are highly desirable for both commercial and scientific interests, but difficult to be realized by traditional photolithographic processes. The current status of scalable nanopatterning technologies is reviewed by L.-S. Chen, J.-X. Tang, and co-workers on page 10353, with a focus on light management by photonic structures on flexible materials in optoelectronic devices. Critical challenges in various patterning techniques are discussed in terms of the resolution, scalability, processing throughput, and use of masks and resists.

Poly(3-hexyl thiophene) (P3HT) can be easily synthesized, demonstrating the large potential to decrease the cost in large-scale synthesis. Thus, the development of novel non-fullerene acceptor to match well with P3HT is urgent and necessary. The first benzotriazole-containing non-fullerene acceptor is designed and synthesized, and high open-circuit voltage (V _oc) of 1.02 V, fill factor (FF) of 0.70, and power conversion efficiency (PCE) of 5.24% are realized, which are remarkably higher than that of P3HT: [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) system (V _oc = 0.59 V, FF = 0.57, and PCE = 3.34%).

Zn(II)–porphyrin sensitizers, coded as SGT-020 and SGT-021, are designed and synthesized through donor structural engineering. The photovoltaic (PV) performances of SGT sensitizer-based dye-sensitized solar cells (DSSCs) are systematically evaluated in a thorough SM315 as a reference sensitizer. The effect of the donor ability and the donor bulkiness on photovoltaic performances is investigated for establishing the structure–performance relationship in the platform of porphyrin-triple bond-benzothiadiazole-acceptor sensitizers. By introducing a more bulky fluorene unit to the amine group in the SM315, the power conversion efficiency (PCE) is enhanced with the increased short-circuit current (J_sc) and open-circuit voltage (V_oc), due to the improved light-harvesting ability and the efficient prevention of charge recombination, respectively. As a consequence, a maximum PCE of 12.11% is obtained for SGT-021, whose PCE is much higher than the 11.70% PCE for SM315. To further improve their maximum efficiency, the first parallel tandem DSSCs employing cobalt electrolyte in the top and bottom cells are demonstrated and an extremely high efficiency of 14% is achieved, which is currently the highest reported value for tandem DSSCs. The series tandem DSSCs give a remarkably high V_oc value of >1.83 V. From this DSSC tandem configuration, 7.4% applied bias photon-to-current efficiency is achieved for solar water splitting.

The effect of the donor ability and bulkiness on DSSC photovoltaic performances is investigated to exceed a world champion porphyrin. The first parallel tandem DSSCs employing cobalt electrolyte are demonstrated with an extremely high efficiency of 14%. The series tandem DSSCs give a remarkably high V_oc value of >1.83 V, achieving 7.4% applied bias photon-to-current efficiency for solar water splitting.