Deping Qian

Fullerene‐Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

High‐Performance Inverted Polymer Solar Cells with Solution‐Processed Titanium Chelate as Electron‐Collecting Layer on ITO Electrode

High-performance inverted polymer solar cells (PSCs) with solution-processed titanium chelate TIPD as electron collecting layer are reported. The power conversion efficiency (PCE) of the inverted PSC with a-TIPD buffer layer with thermal annealing at 150 °C for 10 min reached 7.4% under the illumination of AM1.5, 100 mW/cm(2), which is increased by 16% in comparison with that (6.4%) of the device in the conventional structure. The PCE of 7.4% is the highest among the inverted PSCs reported so far in the literature.

A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics

Small molecule donor/polymer acceptor bulk-heterojunction films with both compounds strongly absorbing have great potential for further enhancement of the performance of organic solar cells. By employing a newly synthesized small molecule donor with a commercially available polymer acceptor in a solution-processed fullerene-free system, a high power conversion efficiency of close to 4% is reported.

Molecular Design toward Efficient Polymer Solar Cells with High Polymer Content

A novel polythiophene derivative, PBT1, was designed, synthesized, and applied in polymer solar cells (PSCs). This work provides a successful example of using molecular structure as a tool to realize optimal photovoltaic performance with high polymer content, thus enabling the realization of efficient photoabsorption in very thin films. As a result, an efficiency of 6.88% was recorded in a PSC with a 75 nm active layer.

Selecting a Donor Polymer for Realizing Favorable Morphology in Efficient Non‐fullerene Acceptor‐based Solar Cells

Fullerene-based polymer solar cells (PSCs), namely utilizing polymers as electron donors and fullerene derivatives as electron acceptors, have been the subject of organic photovoltaic and the predominant type of polymer solar cells in the past decade. [ 1–6 ] Although fullerene derivatives like [6,6]-phenylC 61 (or C 71 )-butyric acid methyl ester (PC 61 BM or PC 71 BM) have made great success, they still have several drawbacks, including poor absorption of visible light for PC 61 BM and high cost for PC 71 BM, which limit their practical applications. [ 7 ] In contrast, non-fullerene acceptors can be easily produced in large scale at low cost and chemically modifi ed with highly tunable absorption spectra and energy levels than those of fullerene derivatives. [ 8,9 ] Encouragingly, Facchetti et al. [ 10 ] reported a record power conversion effi ciency (PCE) of ≈6.4% in polymer:polymer blend-based PSCs, which demonstrated the great potential of fullerene-free PSCs and signifi cantly promoted the research in the fi eld. Beyond polymers, [ 11–16 ] a variety of non-fullerene small molecules [ 17–32 ]

Design rules for minimizing voltage losses in high-efficiency organic solar cells

The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor–acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor–acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.Key optoelectronic properties for donor and acceptor organic semiconductors are identified to obtain organic solar cells with reduced open-circuit voltage losses and high power conversion efficiencies.

Light-induced degradation of fullerenes in organic solar cells: a case study on TQ1:PC71BM

The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (VOC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.