Ligang Yuan

Dipolar cations confer defect tolerance in wide-bandgap metal halide perovskites

Dipolar cations confer defect tolerance in wide-bandgap metal halide perovskites, Published online: 06 August 2018; doi:10.1038/s41467-018-05531-8

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO₂

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO₂, Published online: 13 August 2018; doi:10.1038/s41467-018-05760-x

Two novel wide bandgap copolymers with conjugated selenyl side chains, PBDT‐Se‐TAZ, and PBDTS‐Se‐TAZ, are synthesized successfully for efficient non‐fullerene polymer solar cells (NF‐PSCs). The side chain engineering of alkylthioselenyl group promotes the resulting copolymers to exhibit high PCE of 12.31%.

In this work, the authors design and synthesize two novel wide bandgap copolymers based on selenophene substituted benzo[1,2‐b:4,5‐b']dithiophene (BDTSe) as the donor unit and fluorinated benzotriazole as the acceptor unit for high performance non‐fullerene polymer solar cells (NF‐PSCs). A larger maximum molar extinction coefficient (ϵ) of 8.54 × 10⁴ M⁻¹ cm⁻¹ is achieved when introducing sulfur atom onto the two‐dimensional (2D) BDTSe units, which should realize the better complementary absorption with ITIC as the acceptor, leading to a higher J _sc of 19.51 mA cm⁻². Furthermore, a lower highest occupied molecular orbital (HOMO) energy level with almost no change in bandgap can be also achieved after inserting the sulfur atoms, thus resulting in an enhanced open‐circuit voltage (V _oc) of 0.84 V without sacrificing the short‐current density (J _sc). In addition, the higher crystallinity and optimized morphology are found to be beneficial to more efficient exciton dissociation and charge transport, giving rise to a higher fill factor (FF) of 75.1% and an elevated power conversion efficiency (PCE) of 12.31%. The results indicate that the strategy of alkylthioselenyl side chains on the BDT unit for constructing the donor‐acceptor (D‐A) copolymer donor materials is an excellent approach for realizing highly efficient NF‐PSCs.

Optical transfer matrix formalism simulation is used to model the absorption spectra, exciton generation rate, and optical electric field distribution of the polymer solar cells based on PTB7‐Th:PC₇₁BM. High performance devices are obtained under the guidance of optical transfer matrix formalism simulation. An optimum PCE of 10.60% is obtained with the device based on the WO_x‐HfAcac buffer layer.

Light management is important for improving light absorption within active layers in polymer solar cells (PSCs). Electrode buffer layers play an important role in modulating the distribution of optical electric filed within the photoactive layer. Herein, the authors employ solution‐processed WO_x or ReO_x to substitute the acidic poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the anode buffer layer and ZrAcac or HfAcac to replace Mg as the cathode buffer layer. Optical transfer matrix formalism simulation is used to model the absorption spectra, exciton generation rate, and optical electric field distribution of devices. Simulated results shows that stronger absorption, quicker exciton generation rate, and more reasonable photoelectric field distribution can be achieved in the photoactive layer with solution‐processed buffer layer modification, which results in a higher short‐circuit current density (J _sc). Under the guidance of theoretical simulation, the device with architecture of ITO/WO_x/PTB7‐Th:PC₇₁BM/HfAcac/Al is optimized. Compared with the traditional PEDOT:PSS‐Mg based device, the J _sc is increased from 16.60 to 18.61 mA cm⁻² and the best power conversion efficiency (PCE) is increased from 9.02% to 10.60% for the device with WO_x‐HfAcac modification, which is among the best values reported for fullerene‐based PSCs. The good agreement between simulated and experimental results indicates that optical model is a useful tool for device design and optimization.

Cellulose paper, as one of the four great inventions of China, possesses admirable properties such as biocompatible, biodegradable, and low‐cost, making it a promising alternative to conventional substrates for perovskite solar cells (PSCs). A flexible hole‐transport‐material (HTM)‐free PSC with PCE of 9.05% is fabricated successfully on the cellulose paper for the first time, which could be utilized in wearable devices.

Flexible, biocompatible, and light‐weight power sources are urgently required due to their promising application in wearable electronics. Organic‐inorganic hybrid lead halide perovskite solar cells (PSCs) with their impressive efficiency and scalable processing capability have emerged as promising candidates for efficient and reliable power sources for wearable electronics. However, the progress in developing low‐cost and efficient flexible PSCs has been confined to Poly(ethylene terephthalate) or metal foil substrates and difficulty to design PSCs on other easily accessible low‐cost substrates such as cellulose paper. Herein, the authors report the hole transport material (HTM)‐free flexible PSCs fabricated on abundant, low‐cost, and biocompatible cellulose paper substrate for the first time. The highest PCE of 9.05% for the paper based flexible HTM‐free PSC is achieved and the device could maintain over 75% of its initial PCE after 1000 bending cycles, demonstrating good stability against bending deformation. Our findings provide an avenue to fabricate reliable power source for wearable electronics.

Chloroplatinic acid (H₂PtCl₆) is incorporated into the TiO2 precuror to improve the electrical properties of a compact TiO2 film with the aim to improve the charge carrier extraction and injection efficiency in n‐i‐p perovskite solar cells. As a result, the resulting perovskite solar cells presented a maximum power conversion efficiency as high as 20.05% owing to the obvious improvements of open‐circuit voltages (1.15 V) and fill factor (0.75).

The electron‐transporting layer (ETL) plays a critical role in improving the charge extraction and suppressing the carrier recombination in planar perovskite solar cells (PSCs). Compact titanium dioxide (TiO₂) film is a widely used as an ETL in conventional n‐i‐p PSCs. However, there is still much room for improvement in the electron mobility and reducing the oxygen vacancies of the compact TiO₂ film. Herein, Pt‐doped TiO₂ film with outstanding electron‐transporting property and complete coverage on the substrates is reported by the authors. Pt‐doping results in a tailed band level of TiO₂, which could suppress the charge accumulation at the interface of TiO₂‐Pt/perovskite. Consequently, TiO₂‐Pt ETL based PSCs deliver a power conversion efficiency as high as 20.05% with an open‐circuit voltage of 1.15 V, a fill factor of 0.75, a short‐circuit current density of 23.83 mA cm⁻² and remarkably alleviated hysteresis behavior.

Publisher Correction: High irradiance performance of metal halide perovskites for concentrator photovoltaics

Publisher Correction: High irradiance performance of metal halide perovskites for concentrator photovoltaics, Published online: 13 August 2018; doi:10.1038/s41560-018-0238-5