Chen Weijie

Nature Energy, Published online: 30 May 2022; doi:10.1038/s41560-022-01038-1

Publication date: August 2022

Source: Nano Energy, Volume 99

Author(s): Lin Xie, Jinsheng Zhang, Wei Song, Jinfeng Ge, Dandan Li, Rong Zhou, Jianqi Zhang, Xiaoli Zhang, Daobing Yang, Bencan Tang, Tao Wu, Ziyi Ge

Publication date: August 2022

Source: Nano Energy, Volume 99

Author(s): Shurong Wang, Luo Yan, Weike Zhu, Zhiyuan Cao, Liujiang Zhou, Liming Ding, Feng Hao

Efficient indoor photovoltaics are achieved with wide bandgap metal halide perovskites. The optimal bandgap is first predicted with detailed balanced theory. The non-radiative recombination losses of the mixed-halide perovskites are reduced with both passivation in the bulk and interface with Pb(SCN)₂ and PEABr, respectively, which result in extremely high power conversion efficiency and open-circuit voltage under weak light illumination.

Abstract

Indoor photovoltaics have attracted increasing attention, since they can provide sustainable energy through the recycling of photon energy from household dim lighting. However, solar cells exhibiting high performance under sunlight may not perform well under indoor light conditions, mainly due to the mismatch of the irradiance spectrum. In particular, most of the indoor light sources emit visible photons with negligible near-infrared irradiance. According to the detailed balance theory, the optimal bandgap for indoor photovoltaics should be relatively larger, considering the trade-off between photocurrent and photovoltage losses. In this work, a systematic comparison of the theoretical limits of the conventional and indoor photovoltaics is presented. Then the non-radiative recombination losses are reduced by a synergetic treatment with Pb(SCN)₂ and PEABr, resulting relatively high open circuit voltage of 1.29 V and power conversion efficiency of 17.32% under 1 sun illumination. Furthermore, the devices are fully characterized under weak indoor light (1000 lux, 4000 K LED) achieving a high efficiency of 37.18%, which is promising for real applications.

Publication date: 15 June 2022

Source: Joule, Volume 6, Issue 6

Author(s): Siyang Wang, Liguo Tan, Junjie Zhou, Minghao Li, Xing Zhao, Hang Li, Wolfgang Tress, Liming Ding, Michael Graetzel, Chenyi Yi (易陈谊)

Nature Photonics, Published online: 26 May 2022; doi:10.1038/s41566-022-01006-x

Nature Energy, Published online: 25 May 2022; doi:10.1038/s41560-022-01048-z

Asymmetric substitution of terminal groups is first applied in small-molecule donors. A record efficiency of 16.34% is achieved for binary all-small-molecule organic solar cells. A unique phenomenon of merits integration is reported rather than the balance between V _oc and J _sc, which is generally observed in asymmetric substitution of nonfullerene acceptors.

Abstract

Asymmetric substitution of end-groups is first applied in molecular donors. Three commonly used end-groups of 2-ethylhexyl cyanoacetate (CA), 2-ethylhexyl rhodanine (Reh), and 1H-indene-1,3(2H)-dione (ID) are combined to construct a series of symmetric and asymmetric donors. Correspondingly, the asymmetric donors SM-CA-Reh and SM-CA-ID show largely increased dipole moments (2.14 and 3.39 D, respectively) and enhanced aggregation propensity, as compared to those of symmetric donors of SM-CA, SM-Reh, and SM-ID. Using N3 as acceptor, interestingly, SM-CA-Reh integrates the photovoltaic characteristics of high fill factor (FF) for SM-CA and high short-circuit current density for SM-Reh, and delivers a record power conversion efficiency (PCE) of 16.34% with a high FF of 77.5%, which is much higher than 15.41% for SM-CA and 14.76% for SM-Reh. However, SM-CA-ID and SM-ID give the lower PCE of 8.20% and 2.76%. Characterization results suggest that the π–π interaction mainly dictates the packing morphology of blend films instead of dipole effect or crystallinity. Mono-substitution of Reh facilitates the molecular demixing appropriately but keeps the characteristic of the fine bicontinuous network of SM-CA:N3. SM-CA-Reh:N3 shows more efficient exciton extraction, higher hole transport, and better miscibility. These results well explain the merits integration and improved photovoltaic performance.

Herein, possible ways are presented to improve the performance of triple-mesoscopic hole-conductor-free perovskite-based solar cells, starting from additives for the different layers, posttreatments, and replacing the mesoscopic carbon electrode by mesoporous indium tin oxide.

Hybrid perovskite is an attractive semiconductor material being used intensively in photovoltaic cells for the last 10 years. It can be integrated in several architectures of solar cells, which are based on the concept that the perovskite is sandwiched between an electron selective contact and a hole-selective contact capped by a metal electrode as the back contact. An additional and unique solar cell structure is the mesoporous layers solar cell, which is based on mesoporous TiO₂ following by mesoporous ZrO₂ (or Al₂O₃) and capped by mesoporous carbon or recently by mesoporous indium tin oxide (ITO) electrodes. These solar cells are fabricated by screen printing and the perovskite is applied in the last step by infiltration through the three mesoporous layers. This solar cell structure holds a great promise, due to its fabrication techniques, high stability, and recycling process. In this review, several ways are brought together to improve the performance of these cells, using additives for the different layers, posttreatments, and ways to change the energy level positions to enhance the photovoltaic performance. Also, a new concept of replacing the carbon with a mesoporous ITO electrode is presented, which shows promising results. The review ends with summary and outlook.

Abstract

Studying optoelectronic properties in FAPb_1−x Sn _x I₃ and in FA_0.83Cs_0.17Pb_1−x Sn _x I₃ perovskites as a function of the lead:tin content, Parrott et al. (2018) and Savill et al. (2020) observed the broadest luminescence linewidth and the largest Stokes shift in mixed compositions with Sn <25% and with >85%. It is in contrast to the intuitive expectation of the largest effects of alloy disorder for the 50:50 composition. This comment addresses the alloy disorder caused by statistical local spatial fluctuations of the alloy composition and shows that the largest effects of alloy disorder for perfectly random fluctuations in FAPb_1−x Sn _x I₃ and FA_0.83Cs_0.17Pb_1−x Sn _x I₃ are, in fact, expected for x < 0.25 and for x > 0.85. It can be one of the reasons why Pb-rich and Sn-rich Sn-Pb perovskites typically show shorter photoluminescence (PL) lifetimes, broader emission, increased Stokes shifts, reduced PL quantum yield, and higher Urbach tails, compared with their lead-only counterparts.

Nature Communications, Published online: 20 May 2022; doi:10.1038/s41467-022-30127-8