Ligang Yuan

A series of PBDB-TTn random donor copolymers is synthesized, consisting of an electron-deficient benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) unit and different ratios of two electron-rich benzo[1,2-b:4,5-b′]dithiophene (BDT) and thieno[3,2-b]thiophene (TT) units, with intention to modulate the intrachain and/or interchain interactions and ultimately bulk-heterojunction morphology evolution. A comparative study using 4 × 2 polymer solar cell (PSC) performance maps and each of the [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) and the fused-aromatic-ring-based molecule (m-ITIC) acceptors are carried out. Given the similarities in their absorption ranges and energy levels, the PBDB-TTn copolymers clearly reveal a change in the absorption coefficients upon optimization of the BDT to TT ratio in the backbone. Among the given acceptor combination sets, superior performances are observed in the case of PBDB-TT5 blended with PC₇₁BM (8.34 ± 0.10%) or m-ITIC (11.10 ± 0.08%), and the dominant factors causing power conversion efficiency differences in them are found to be distinctly different. For example, the performances of PC₇₁BM-based PSCs are governed by size and population of face-on crystallites, while intermixed morphology without the formation of large phase-separated aggregates is the key factor for achieving high-performance m-ITIC-based PSCs. This study presents a new sketch of structure–morphology–performance relationships for fullerene- versus nonfullerene-based PSCs.

BDD-based four copolymers PBDD-TTn which contained BDT, TT, and BDD are synthesized and operated with two acceptors, PC₇₁BM and m-ITIC. Two systems have different operating mechanisms, and simultaneously high-performances 8.44% for PC₇₁BM and 11.18% for m-ITIC are obtained.

Many years since the booming of research on perovskite solar cells (PSCs), the hybrid perovskite materials developed for photovoltaic application form three main categories since 2009: (i) high-performance unstable lead-containing perovskites, (ii) low-performance lead-free perovskites, and (iii) moderate performance and stable lead-containing perovskites. The search for alternative materials to replace lead leads to the second group of perovskite materials. To date, a number of these compounds have been synthesized and applied in photovoltaic devices. Here, lead-free hybrid light absorbers used in PV devices are focused and their recent developments in related solar cell applications are reviewed comprehensively. In the first part, group 14 metals (Sn and Ge)-based perovskites are introduced with more emphasis on the optimization of Sn-based PSCs. Then concerns on halide hybrids of group 15 metals (Bi and Sb) are raised, which are mainly perovskite derivatives. At the same time, transition metal Cu-based perovskites are also referred. In the end, an outlook is given on the design strategy of lead-free halide hybrid absorbers for photovoltaic applications. It is believed that this timely review can represent our unique view of the field and shed some light on the direction of development of such promising materials.

Real clean energy means the whole process of its generation has low environmental and health impact. Recent progress of five types of hybrid halide absorbers against the thorny problem of lead toxicity is introduced based on the state-of-the-art perovskite solar cells (PSCs). Can we make high-efficiency PSCs without being poisoned?

A new type of high boiling-point additive, UV absorbent benzophenone, is employed into fullerene and nonfullerene organic solar cells, to simultaneously improve the efficiency and stability.

By embedding pyran rings in PDT, a novel ladder-type heteroarene, BDTP, is constructed to design a high-performance non-fullerene acceptor NBDTP for organic photovoltaic applications. The fused pyran rings endows NBDTP with favorable energy-level alignment and proper blend morphology, delivering a power conversion efficiency of over 10%, suggesting the BDTP core is a very promising building block for organic optoelectronic applications.

Semi-transparent plastic solar cells are currently highly attractive for their potential as the most prominent components for building-integrated photovoltaics. However, the power conversion efficiency (PCE) of semi-transparent plastic solar cells still lags behind due to the lack of a suitable transparent top electrode which can be easily fabricated. Here, we demonstrate high performance semi-transparent plastic solar cells by introducing an oxide-metal-oxide (OMO) multilayer composed of MoO₃ and Ag as a transparent top electrode. Because the conductivity of the OMO electrode is governed by an intermediate Ag layer sandwiched between 2 MoO₃ layers, the PCE also strongly depends on the thickness of the intermediate Ag layer in the OMO electrode. By controlling the thickness of Ag layer, we obtained various PCE values from 4.5% with ~50% maximum transparency in the visible region to 9.1% with ~5% maximum transparency in the visible region. In addition, in order to get closer to practical application, 2 sizes of mini-module devices were fabricated on a larger (10.0 cm × 10.0 cm) substrate for outdoor operation and small-sized (7.0 cm × 5.0 cm) substrates for indoor operation were demonstrated using 3 materials of different color.

High efficient semi-transparent plastic solar cells based on oxide-metal-oxide were demonstrated from a single unit cell device to 10.0 cm × 10.0 cm sized mini-module devices. The semi-transparent solar cell which has a maximum transparency of 25% in visible region yielded a power conversion efficiency of 8.4%.

Organic–inorganic perovskites are well suited for optoelectronic applications. In particular, perovskite single and perovskite tandem solar cells with silicon are close to their market entry. Despite their swift rise in efficiency to more than 21%, solar cell lifetimes are way below the needed 25 years. In fact, comparison of the time when the device performance has degraded to 80% of its initial value (T₈₀ lifetime) of numerous solar cells throughout the literature reveals a strongly reduced stability under illumination. Herein, the various detrimental effects are discussed. Most notably, moisture- and heat-related degradation can be mitigated easily by now. Recently, however, several photoinduced degradation mechanisms have been observed. Under illumination, mixed perovskites tend to phase segregate, while, further, oxygen catalyzes deprotonation of the organic cations. Additionally, during illumination photogenerated charge can be trapped in the NH antibonding orbitals causing dissociation of the organic cation. On the other hand, organic–inorganic perovskites exhibit a high radiation hardness that is superior to crystalline silicon. Here, the proposed degradation mechanisms reported in the literature are thoroughly reviewed and the microscopic mechanisms and their implications for solar cells are discussed.

T₈₀ lifetimes of organic–inorganic perovskite solar cells are strongly reduced under illumination. Various degradation mechanisms are therefore discussed throughout the literature. Degradation by moisture or heat is well understood and mitigation possible. Photoinduced phase segregation and photoinduced dissociation of the organic cation, however, remain unsolved. Recent observations enlighten the underlying microscopic mechanisms and may pave the way for stable perovskites.

Employing a layer of bulk-heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite-based solar cells, instead of using tandem devices or near infrared (NIR)-absorbing Sn-containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short-circuit current (J_SC) and fill factor (FF). To find an appropriate NIR-absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase J_SC, but also possess suitable energy levels and high mobility to afford high V_OC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well-matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high V_oc, J_SC, and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.

A highly efficient organic photovoltaics/perovskite hybrid solar cell is demonstrated by blending a new conjugated porphyrin-based small molecule with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to function as an efficient bulk-heterojunction layer. The extended photoresponse, matched energy levels, and high hole mobility derived from the optimized bulk-heterojunction morphology contribute to the record-high efficiency of 19.02% in these hybrid devices.

Perovskite semiconductors have emerged as competitive candidates for photovoltaic applications due to their exceptional optoelectronic properties. However, the impact of moisture instability on perovskite films is still a key challenge for perovskite devices. While substantial effort is focused on preventing moisture interaction during the fabrication process, it is demonstrated that low moisture sensitivity, enhanced crystallization, and high performance can actually be achieved by exposure to high water content (up to 25 vol%) during fabrication with an aqueous-containing perovskite precursor. The perovskite solar cells fabricated by this aqueous method show good reproducibility of high efficiency with average power conversion efficiency (PCE) of 18.7% and champion PCE of 20.1% under solar simulation. This study shows that water–perovskite interactions do not necessarily negatively impact the perovskite film preparation process even at the highest efficiencies and that exposure to high contents of water can actually enable humidity tolerance during fabrication in air.

Perovskite solar cells fabricated by an aqueous-containing precursor method show good reproducibility with a high average power conversion efficiency (PCE) of 18.7% and a champion PCE of 20.1%. The study shows that water–perovskite interactions do not necessarily negatively impact perovskites even at the highest efficiencies and that exposure to high contents of water can actually enable humidity tolerance during fabrication in air.

Organic–inorganic lead halide perovskites are promising optoelectronic materials resulting from their significant light absorption properties and unique long carrier dynamics, such as a long carrier lifetime, carrier diffusion length, and high carrier mobility. These advantageous properties have allowed for the utilization of lead halide perovskite materials in solar cells, LEDs, photodetectors, lasers, etc. To further explore their potential, intrinsic properties should be thoroughly investigated. Single crystals with few defects are the best candidates to disclose a variety of interesting and important properties of these materials, ultimately, showing the increased importance of single-crystalline perovskite research. In this review, recent progress on the crystallization, investigation, and primary device applications of single-crystalline perovskites are summarized and analyzed. Further improvements in device design and preparation are also discussed.

Single-crystalline perovskites show better and more intrinsic optoelectronic properties, which are critical for devices design and performance prediction. In this review, the crystal growth, property investigations as well as device application of single crystals are summarized and discussed. At the end, the strategies for improving the performances of single-crystalline devices are outlooked.

Carbon quantum dots (CQDs) and PbS-EDT:CuI (PbS QDs treated by EDT:CuI solution) are integrated in PbS QDs solar cells to enhance electron extraction and hole extraction, respectively. This strategy significantly improves the power conversion efficiency to 9.95% from 8.60%. The designed device also shows very high air stability.

Performance of organic photovoltaic devices, incorporating three different polymer/fullerene derivative blends, is investigated under low-level lighting conditions. The devices exhibit much higher power conversion efficiencies under indoor lighting conditions than they do under sunlight. The results indicate that the value of open-circuit voltage is the most critical factor affecting the suitability for low-power indoor applications.